Vasoregression is a hallmark of vascular eye diseases but the mechanisms involved are still largely unknown. We have recently characterized a rat ciliopathy model which develops primary photoreceptor degeneration and secondary vasoregression. To improve the understanding of secondary vasoregression in retinal neurodegeneration, we used microarray techniques to compare gene expression profiles in this new model before and after retinal vasoregression. Differential gene expression was validated by quantitative RT-PCR, Western blot and immunofluorescence. Of the 157 genes regulated more than twofold, the MHC class II invariant chain CD74 yielded the strongest upregulation, and was allocated to activated microglial cells close to the vessels undergoing vasoregression. Pathway clustering identified genes of the immune system including inflammatory signaling, and components of the complement cascade upregulated during vasoregression. Together, our data suggest that microglial cells involved in retinal immune response participate in the initiation of vasoregression in the retina.
Retinal degeneration in transgenic rats that express a mutant cilia gene polycystin-2 (CMV-PKD2(1/703)HA) is characterized by initial photoreceptor degeneration and glial activation, followed by vasoregression and neuronal degeneration (Feng et al., 2009, PLoS One 4: e7328). It is unknown whether glial activation contributes to neurovascular degeneration after photoreceptor degeneration. We characterized the reactivity of Müller glial cells in retinas of rats that express defective polycystin-2.
Age-matched Sprague-Dawley rats served as control. Retinal slices were immunostained for intermediate filaments, the potassium channel Kir4.1, and aquaporins 1 and 4. The potassium conductance of isolated Müller cells was recorded by whole-cell patch clamping. The osmotic swelling characteristics of Müller cells were determined by superfusion of retinal slices with a hypoosmotic solution.
Müller cells in retinas of transgenic rats displayed upregulation of GFAP and nestin which was not observed in control cells. Whereas aquaporin-1 labeling of photoreceptor cells disappeared along with the degeneration of the cells, aquaporin-1 emerged in glial cells in the inner retina of transgenic rats. Aquaporin-4 was upregulated around degenerating photoreceptor cells. There was an age-dependent redistribution of Kir4.1 in retinas of transgenic rats, with a more even distribution along glial membranes and a downregulation of perivascular Kir4.1. Müller cells of transgenic rats displayed a slight decrease in their Kir conductance as compared to control. Müller cells in retinal tissues from transgenic rats swelled immediately under hypoosmotic stress; this was not observed in control cells. Osmotic swelling was induced by oxidative-nitrosative stress, mitochondrial dysfunction, and inflammatory lipid mediators.
Cellular swelling suggests that the rapid water transport through Müller cells in response to osmotic stress is altered as compared to control. The dislocation of Kir4.1 will disturb the retinal potassium and water homeostasis, and osmotic generation of free radicals and inflammatory lipids may contribute to neurovascular injury.
Axotomy of central neurons leads to functional and structural alterations which largely revert when neural progenitor cells (NPCs) are implanted in the lesion site. The new microenvironment created by NPCs in the host tissue might modulate in the damaged neurons the expression of a high variety of molecules with relevant roles in the repair mechanisms, including neurotrophic factors. In the present work, we aimed to analyze changes in neurotrophic factor expression in axotomized neurons induced by NPC implants. For this purpose, we performed immunofluorescence followed by confocal microscopy analysis for the detection of vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and nerve growth factor (NGF) on brainstem sections from rats with axotomy of abducens internuclear neurons that received NPC implants (implanted group) or vehicle injections (axotomized group) in the lesion site. Control abducens internuclear neurons were strongly immunoreactive to VEGF and BDNF but showed a weak staining for NT-3 and NGF. Comparisons between groups revealed that lesioned neurons from animals that received NPC implants showed a significant increase in VEGF content with respect to animals receiving vehicle injections. However, the immunoreactivity for BDNF, which was increased in the axotomized group as compared to control, was not modified in the implanted group. The modifications induced by NPC implants on VEGF and BDNF content were specific for the population of axotomized abducens internuclear neurons since the neighboring abducens motoneurons were not affected. Similar levels of NT-3 and NGF immunolabeling were obtained in injured neurons from axotomized and implanted animals. Among all the analyzed neurotrophic factors, only VEGF was expressed by the implanted cells in the lesion site. Our results point to a role of NPC implants in the modulation of neurotrophic factor expression by lesioned central neurons, which might contribute to the restorative effects of these implants.
The polycystin family of transient receptor potential (TRP) channels form Ca2+ regulated cation channels with distinct subcellullar localizations and functions. As part of heteromultimeric channels and multi-protein complexes, polycystins control intracellular Ca2+ signals and more generally the translation of extracellular signals and stimuli to intracellular responses. Polycystin-2 channels have been cloned from retina, but their distribution and function in retinal ganglion cells (RGCs) have not yet been established. In the present study, we determined cellular and subcellular localization as well as functional properties of polycystin-2 channels in RGCs. Polycystin-2 expression and distribution in RGCs was assessed by immunohistochemistry on vertical cryostat section of mouse retina as well as primary cultured mouse RGCs, using fluorescence microscopy. Biophysical and pharmacological properties of polycystin-2 channels isolated from primary cultured RGCs were determined using planar lipid bilayer electrophysiology. We detected polycystin-2 immunoreactivity both in the ganglion cell layer as well as in primary cultured RGCs. Subcellular analysis revealed strong cytosolic localization pattern of polycystin-2. Polycystin-2 channel current was Ca2+ activated, had a maximum slope conductance of 114 pS and could be blocked in a dose-dependent manner by increasing concentrations of Mg2+. The cytosolic localization of polycystin-2 in RGCs is in accordance with its function as intracellular Ca2+ release channel. We conclude that polycystin-2 forms functional channels in RGCs, of which biophysical and pharmacological properties are similar to polycystin-2 channels reported for other tissues and organisms. Our data suggest a potential role for polycystin-2 in RGC Ca2+ signaling.
polycystin; transient receptor potential channel; retinal ganglion cells; calcium; electrophysiology
Recently, multiple neurotrophic/growth factors have been proposed to play an important role in the therapeutic action of antidepressants. In this study, we prepared astrocyte- and neuron-enriched cultures from the neonatal rat cortex, and examined the changes in neurotrophic/growth factor expression by antidepressant treatment using real-time PCR. Treatment with amitriptyline (a tricyclic antidepressant) significantly increased the expression of fibroblast growth factor-2 (FGF-2), brain-derived neurotrophic factor, vascular endothelial growth factor and glial cell line-derived neurotrophic factor mRNA with a different time course in astrocyte cultures, but not in neuron-enriched cultures. Only the expression of FGF-2 was higher in astrocyte cultures than in neuron-enriched cultures. We focused on the FGF-2 production in astrocytes. Several different classes of antidepressants, but not non-antidepressants, also induced FGF-2 mRNA expression. Noradrenaline (NA) is known to induce FGF-2 expression in astrocyte cultures, as with antidepressants. Therefore, we also assessed the mechanism of NA-induced FGF-2 expression, in comparison to amitriptyline. NA increased the FGF-2 mRNA expression via α1 and β-adrenergic receptors; however, the amitriptyline-induced FGF-2 mRNA expression was not mediated via these adrenergic receptors. Furthermore, the amitriptyline-induced FGF-2 mRNA expression was completely blocked by cycloheximide (an inhibitor of protein synthesis), while the NA-induced FGF-2 mRNA was not. These data suggest that the regulation of FGF-2 mRNA expression by amitriptyline was distinct from that by NA. Taken together, antidepressant-stimulated astrocytes may therefore be important mediators that produce several neurotrophic/growth factors, especially FGF-2, through a monoamine-independent and a de novo protein synthesis-dependent mechanism.
There is considerable evidence from our lab and others for a functional link between β-adrenergic receptor and insulin receptor signaling pathways in retina. Furthermore, we hypothesize that this link may contribute to lesions similar to diabetic retinopathy in that the loss of adrenergic input observed in diabetic retinopathy may disrupt normal anti-apoptotic insulin signaling, leading to retinal cell death. Our studies included assessment of neural retina function (ERG), vascular degeneration, and Müller glial cells (which express only β1 and β2-adrenergic receptor subtypes). In the current study, we produced β2-adrenergic receptor knockout mice to examine this deletion on retinal neurons and vasculature, and to identify specific pathways through which β2-adrenergic receptor modulates insulin signaling. As predicted from our hypothesis, β2-adrenergic receptor knockout mice display certain features similar to diabetic retinopathy. In addition, loss of β2-adrenergic input resulted in an increase in TNFα, a key inhibitor of insulin receptor signaling. Increased TNFα may be associated with insulin-dependent production of the anti-apoptotic factor, Akt. Since the effects occurred in vivo under normal glucose conditions, we postulate that aspects of the diabetic retinopathy phenotype might be triggered by loss of β2-adrenergic receptor signaling.
We are investigating a double transgenic rat (dTGR) model, in which rats transgenic for the human angiotensinogen and renin genes are crossed. These rats develop moderately severe hypertension but die of end-organ cardiac and renal damage by week 7. The heart shows necrosis and fibrosis, whereas the kidneys resemble the hemolytic-uremic syndrome vasculopathy. Surface adhesion molecules (ICAM-1 and VCAM-1) are expressed early on the endothelium, while the corresponding ligands are found on circulating leukocytes. Leukocyte infiltration in the vascular wall accompanies PAI-1, MCP-1, iNOS and Tissue Factor expression. Furthermore we show evidence that Ang II causes the upregulation of NF-kB in our model.
We started PDTC-treatment on four weeks old dTGR (200 mg/kg sc) and age-matched SD rats.. Blood-pressure- and albuminuria- measurements were monitored during the treatement period (four weeks). The seven weeks old animals were killed, hearts and kidneys were isolated and used for immunohistochemical-and electromobility shift assay analsis.
Chronic treatment with the antioxidant PDTC decreased blood pressure (162 ± 8 vs. 190 ± 7 mm Hg, p = 0.02). Cardiac hypertrophy index was significantly reduced (4.90 ± 0.1 vs. 5.77 ± 0.1 mg/g, p < 0.001) compared to dTGR. PDTC reduced 24 h albuminuria by 85 % (2.7 ± 0.5 vs. 18.0 ± 3.4 mg/d, p < 0.001) and prevented death significantly. Vascular injury was ameliorated in small renal and cardiac vessels. PDTC inhibited NF-κB binding activity in heart and kidney. Immunohistochemical analysis shows increased expression of the p65 NF-κB subunit in the endothelium, smooth muscles cells of damaged small vessels, infiltrated cells, glomeruli, tubuli and collecting ducts of dTGR. PDTC markedly reduced the immunoreactivity of p65.
Our data show that inhibition of NF-κB by PDTC markedly reduces inflammation, iNOS expression in the dTGR most likely leading to decreased cytotoxicity, and cell proliferation. Thus, NF-κB activation plays an important role in ANG II-induced end-organ damage.
Bladder sensation is mediated by lumbosacral dorsal root ganglion neurons and is essential for normal voiding and nociception. Numerous electrophysiological, structural, and molecular changes occur in these neurons following inflammation. Defining which neurons undergo these changes is critical for understanding the mechanism underlying bladder pain and dysfunction. Our first aim was to define the chemical classes of bladder sensory neurons that express receptors for the endogenous modulators of nociceptor sensitivity, glial cell line-derived neurotrophic factor (GDNF), the related neurotrophic factor, artemin, and estrogens. Bladder sensory neurons of adult female Sprague-Dawley rats were identified with retrograde tracer. Diverse groups of neurons express these receptors, and some neurons express receptors for both neurotrophic factors and estrogens. Lumbar and sacral sensory neurons showed some distinct differences in their expression profile. We also distinguished the chemical profile of myelinated and unmyelinated bladder sensory neurons. Our second aim was to identify bladder sensory neurons likely to be undergoing structural remodeling during inflammation. Following systemic administration of cyclophosphamide (CYP), its renal metabolite acrolein causes transient urothelial loss, exposing local afferent terminals to a toxic environment. CYP induced expression of the injury-related immediate-early gene product, activating transcription factor-3 (ATF-3), in a small population of sacral nitrergic bladder sensory neurons. In conclusion, we have defined the bladder sensory neurons that express receptors for GDNF, artemin and estrogens. Our study has also identified a sub-population of sacral sensory neurons that are likely to be undergoing structural remodeling during acute inflammation of the bladder. Together these results contribute to increased understanding of the neurons that are known to be involved in pain modulation and hyperreflexia during inflammation.
dorsal root ganglion; painful bladder syndrome; pelvic pain; visceral pain; steroid; cystitis; interstitial cystitis; inflammatory pain
Recent studies have described a novel type of glial cell that is scattered across the inner layers of the avian retina and possibly the retinas of primates. These cells have been termed Non-astrocytic Inner Retinal Glial (NIRG) cells. These cells are stimulated by insulin-like growth factor 1 (IGF1) to proliferate, migrate distally into the retina, and become reactive. These changes in glial activity correlate with increased susceptibility of retinal neurons and Müller glia to excitotoxic damage. The purpose of this study was to further study the NIRG cells in retinas treated with IGF1 or acute damage. In response to IGF1, the reactivity, proliferation and migration of NIRG cells persists through 3 days after treatment. At 7 days after treatment, the numbers and distribution of NIRG cells returns to normal, suggesting that homeostatic mechanisms are in place within the retina to maintain the numbers and distribution of these glial cells. By comparison, IGF1-induced microglial reactivity persists for at least 7 days after treatment. In damaged retinas, we find a transient accumulation of NIRG cells, which parallels the accumulation of reactive microglia, suggesting that the reactivity of NIRG cells and microglia are linked. When the microglia are selectively ablated by the combination of interleukin 6 and clodronate-liposomes, the NIRG cells down-regulate transitin and perish within the following week, suggesting that the survival and phenotype of NIRG cells are somehow linked to the microglia. We conclude that the abundance, reactivity and retinal distribution of NIRG cells can be dynamic, are regulated by homoestatic mechanisms and are tethered to the microglia.
Cilia are endowed with membrane receptors, channels, and signaling components whose localization and function must be tightly controlled. In primary cilia of mammalian kidney epithelia and sensory cilia of Caenorhabditis elegans neurons, polycystin-1 (PC1) and transient receptor polycystin-2 channel (TRPP2 or PC2), function together as a mechanosensory receptor-channel complex. Despite the importance of the polycystins in sensory transduction, the mechanisms that regulate polycystin activity and localization, or ciliary membrane receptors in general, remain poorly understood. We demonstrate that signal transduction adaptor molecule STAM-1A interacts with C. elegans LOV-1 (PC1), and that STAM functions with hepatocyte growth factor–regulated tyrosine kinase substrate (Hrs) on early endosomes to direct the LOV-1-PKD-2 complex for lysosomal degradation. In a stam-1 mutant, both LOV-1 and PKD-2 improperly accumulate at the ciliary base. Conversely, overexpression of STAM or Hrs promotes the removal of PKD-2 from cilia, culminating in sensory behavioral defects. These data reveal that the STAM-Hrs complex, which down-regulates ligand-activated growth factor receptors from the cell surface of yeast and mammalian cells, also regulates the localization and signaling of a ciliary PC1 receptor-TRPP2 complex.
Inherited retinal degenerations afflict 1 in 3,500 individuals and are a heterogeneous group of diseases that result in profound vision loss, usually the result of retinal neuronal apoptosis. Atrophic changes in the retinal vasculature are also observed in many of these degenerations. While it is thought that this atrophy is secondary to diminished metabolic demand in the face of retinal degeneration, the precise relationship between the retinal neuronal and vascular degeneration is not clear. In this study we demonstrate that whenever a fraction of mouse or human adult bone marrow–derived stem cells (lineage-negative hematopoietic stem cells [Lin– HSCs]) containing endothelial precursors stabilizes and rescues retinal blood vessels that would ordinarily completely degenerate, a dramatic neurotrophic rescue effect is also observed. Retinal nuclear layers are preserved in 2 mouse models of retinal degeneration, rd1 and rd10, and detectable, albeit severely abnormal, electroretinogram recordings are observed in rescued mice at times when they are never observed in control-treated or untreated eyes. The normal mouse retina consists predominantly of rods, but the rescued cells after treatment with Lin– HSCs are nearly all cones. Microarray analysis of rescued retinas demonstrates significant upregulation of many antiapoptotic genes, including small heat shock proteins and transcription factors. These results suggest a new paradigm for thinking about the relationship between vasculature and associated retinal neuronal tissue as well as a potential treatment for delaying the progression of vision loss associated with retinal degeneration regardless of the underlying genetic defect.
Basic fibroblast growth factor (bFGF) is a pleiotropic cytokine with pro-angiogenic and neurotrophic effects. The angioregulatory role of this molecule may become especially significant in retinal neovascularization, which is a hallmark of a number of ischemic eye diseases. This study was undertaken to reveal expression characteristics of bFGF, produced by retinal glial (Müller) cells, and to determine conditions under which glial bFGF may stimulate the proliferation of retinal microvascular endothelial cells. Immunofluorescence labeling detected bFGF in Müller cells of the rat retina and in acutely isolated Müller cells with bFGF levels, which increased after ischemia-reperfusion in postischemic retinas. In patients with proliferative diabetic retinopathy or myopia, the immunoreactivity of bFGF co-localized to glial fibrillary acidic protein (GFAP)-positive cells in surgically excised retinal tissues. RT-PCR and ELISA analyses indicated that cultured Müller cells produce bFGF, which is elevated under hypoxia or oxidative stress, as well as under stimulation with various growth factors and cytokines, including pro-inflammatory factors. When retinal endothelial cells were cultured in the presence of media from hypoxia (0.2%)-conditioned Müller cells, a distinct picture of endothelial cell proliferation emerged. Media from 24-h cultured Müller cells inhibited proliferation, whereas 72-h conditioned media elicited a stimulatory effect. BFGF-neutralizing antibodies suppressed the enhanced endothelial cell proliferation to a similar extent as anti-VEGF antibodies. Furthermore, phosphorylation of extracellular signal-regulated kinases (ERK−1/−2) in retinal endothelial cells was increased when the cells were cultured in 72-h conditioned media, while neutralizing bFGF attenuated the activation of this signaling pathway. These data provide evidence that retinal (glial) Müller cells are major sources of bFGF in the ischemic retina. Müller cells under physiological conditions or transient hypoxia seem to provide an anti-angiogenic environment, but long-lasting hypoxia causes the release of bFGF, which might significantly co-stimulate neovascularization in the retina.
The purpose of this study was to determine whether the expression of ER stress-related factors IRE1α, apoptosis signal-regulating kinase 1 (ASK1), SAPK/ERK kinase 1 (SEK1) and c-Jun N-terminal kinase (JNK) is associated with the damaged retinal neurons induced by ischemia-reperfusion injury. After 60 minutes of ischemia, the rat retinas were reperfused, and retinas were isolated and fixed after 6, 9, 12, 18, and 24 hours, and 2, 5, and 9 days of reperfusion. Cryosections were immunostained with Fluoro-Jade B, a degenerating neuron marker to label degenerating neurons. Semi-quantitative analysis of the expression of IRE1α, ASK1, SEK1, and JNK were performed in both control and ischemic retinas. In ischemic retinas, the intensities of IRE1α immunoreactivity in the ganglion cell layer (GCL) were significantly higher than in the control retinas. In ischemic retinas, the numbers of SEK1-, ASK1-, and JNK-positive cells were significantly increased in the GCL compared to those in the control retinas. In addition, the cells that were positive for SEK1-, ASK1-, and JNK were also positive for Fluoro-Jade B-positive cells. These results indicate that the increased expression of ER stress-related factors was, in part, associated with the retinal neuronal abnormalities after ischemia-reperfusion injury in rat retinas.
endoplasmic reticulum; IRE1α; apoptosis signal-regulating kinase 1; SAPK/ERK kinase 1; c-Jun N-terminal kinase; Fluoro-Jade B; ischemia-reperfusion injury
Ciliary neurotrophic factor (CNTF), a member of the interleukin-6 cytokine family, has been implicated in the development, differentiation and survival of retinal neurons. The mechanisms of CNTF action as well as its cellular targets in the retina are poorly understood. It has been postulated that some of the biological effects of CNTF are mediated through its action via retinal glial cells; however, molecular changes in retinal glia induced by CNTF have not been elucidated. We have, therefore, examined gene expression dynamics of purified Müller (glial) cells exposed to CNTF in vivo.
Müller cells were flow-sorted from mgfap-egfp transgenic mice one or three days after intravitreal injection of CNTF. Microarray analysis using RNA from purified Müller cells showed differential expression of almost 1,000 transcripts with two- to seventeen-fold change in response to CNTF. A comparison of transcriptional profiles from Müller cells at one or three days after CNTF treatment showed an increase in the number of transcribed genes as well as a change in the expression pattern. Ingenuity Pathway Analysis showed that the differentially regulated genes belong to distinct functional types such as cytokines, growth factors, G-protein coupled receptors, transporters and ion channels. Interestingly, many genes induced by CNTF were also highly expressed in reactive Müller cells from mice with inherited or experimentally induced retinal degeneration. Further analysis of gene profiles revealed 20–30% overlap in the transcription pattern among Müller cells, astrocytes and the RPE.
Our studies provide novel molecular insights into biological functions of Müller glial cells in mediating cytokine response. We suggest that CNTF remodels the gene expression profile of Müller cells leading to induction of networks associated with transcription, cell cycle regulation and inflammatory response. CNTF also appears to function as an inducer of gliosis in the retina.
Glial cell line-derived neurotrophic factor (GDNF) is neuroprotective of retinal neurons, and transduced retinal progenitor cells (RPCs) can deliver this cytokine for the treatment of retinal diseases, yet the potential effects of GDNF on RPCs have received little attention.
Murine RPCs were assessed under multiple conditions in the presence or absence of epidermal growth factor (EGF, 20 ng/ml) and/or GDNF (10 ng/ml) using a variety of techniques, including live-cell imaging, caspase-3 activity assay, whole genome microarray, quantitative polymerase chain reaction (qPCR), and western blotting.
Live monitoring revealed that formation of initial aggregates resulted largely from the collision and adherence of dissociated RPCs, as opposed to clonal proliferation. Spheres enlarged in size and number, with more reaching the threshold criteria for cross-sectional areas in the EGF+GDNF condition. Proliferation was measurably augmented in association with EGF+GDNF, and Ki-67 expression was modestly increased (1.07 fold), as were hairy and enhancer of split 5 (Hes5), mammalian achaete-scute homolog 1 (Mash1), and Vimentin. However, global gene expression did not reveal a notable treatment-related response, and the expression of the majority of progenitor and lineage markers examined remained stable. GDNF reduced RPC apoptosis, compared to complete growth-factor withdrawal, although it could not by itself sustain mitotic activity.
These data support the feasibility of developing GDNF-transduced RPCs as potential therapeutic agents for use in retinal diseases.
Neuronal activity evokes localized changes in blood flow, a response termed neurovascular coupling. One widely recognized hypothesis of neurovascular coupling holds that glial cell depolarization evoked by neuronal activity leads to the release of K+ onto blood vessels (K+ siphoning) and to vessel relaxation. We now present two direct tests of this glial cell-K+ siphoning hypothesis of neurovascular coupling. Potassium efflux was evoked from glial cells in the rat retina by applying depolarizing current pulses to individual cells. Glial depolarizations as large as 100 mV produced no change in the diameter of adjacent arterioles. We also monitored light-evoked vascular responses in Kir4.1 knock-out mice, where functional Kir K+ channels are absent from retinal glial cells. The magnitude of light-evoked vasodilations was identical in Kir4.1 knock-out and wild-type animals. Contrary to the hypothesis, the results demonstrate that glial K+ siphoning in the retina does not contribute significantly to neurovascular coupling.
blood flow; glia; astrocytes; Müller cells; Kir4.1; potassium siphoning; retina
Iron accumulation is associated with age-related neurodegenerations and may contribute to age-related increased susceptibility of neurons to damage. We compared young and old rodent retinas to assess iron homeostasis during normal aging and the effects of increased iron on the susceptibility of retinal neurons to degeneration. Retinal iron was significantly increased with age. Quantitative RT-PCR showed that transferrin and ferritin genes were upregulated in the aged retina. At the protein level, we found decreased transferrin, and increased transferrin receptor, ferritin, ferroportin, and ceruloplasmin in the aged retina. These results support an increased steady state of iron with age in the retina. We tested susceptibility of retinal neurons with increased intracellular iron to damage in vitro. Exposure of RGC-5 cells to increased iron potentiated the neurotoxicity induced by paraquat, glutamate and TNF α. Our results demonstrate that iron homeostasis in the retina is altered with age and suggest that iron accumulation, due to altered levels of iron regulatory proteins in the aged retina, could be a susceptibility factor in age-related retinal diseases.
iron; aging; susceptibility; neurodegeneration; RGC-5; stress
Recombinant adeno-associated viral (rAAV) vectors can be used to introduce neurotrophic genes into injured CNS neurons, promoting survival and axonal regeneration. Gene therapy holds much promise for the treatment of neurotrauma and neurodegenerative diseases; however, neurotrophic factors are known to alter dendritic architecture, and thus we set out to determine whether such transgenes also change the morphology of transduced neurons. We compared changes in dendritic morphology of regenerating adult rat retinal ganglion cells (RGCs) after long-term transduction with rAAV2 encoding: (i) green fluorescent protein (GFP), or (ii) bi-cistronic vectors encoding GFP and ciliary neurotrophic factor (CNTF), brain-derived neurotrophic factor (BDNF) or growth-associated protein-43 (GAP43). To enhance regeneration, rats received an autologous peripheral nerve graft onto the cut optic nerve of each rAAV2 injected eye. After 5–8 months, RGCs with regenerated axons were retrogradely labeled with fluorogold (FG). Live retinal wholemounts were prepared and GFP positive (transduced) or GFP negative (non-transduced) RGCs injected iontophoretically with 2% lucifer yellow. Dendritic morphology was analyzed using Neurolucida software. Significant changes in dendritic architecture were found, in both transduced and non-transduced populations. Multivariate analysis revealed that transgenic BDNF increased dendritic field area whereas GAP43 increased dendritic complexity. CNTF decreased complexity but only in a subset of RGCs. Sholl analysis showed changes in dendritic branching in rAAV2-BDNF-GFP and rAAV2-CNTF-GFP groups and the proportion of FG positive RGCs with aberrant morphology tripled in these groups compared to controls. RGCs in all transgene groups displayed abnormal stratification. Thus in addition to promoting cell survival and axonal regeneration, vector-mediated expression of neurotrophic factors has measurable, gene-specific effects on the morphology of injured adult neurons. Such changes will likely alter the functional properties of neurons and may need to be considered when designing vector-based protocols for the treatment of neurotrauma and neurodegeneration.
The authors examined the neuroprotective effect of BDNF-secreting mesenchymal stem cells on retina and optic nerve function and structure in hypertensive eyes.
To evaluate the ability of mesenchymal stem cells (MSCs) engineered to produce and secrete brain-derived neurotrophic factor (BDNF) to protect retinal function and structure after intravitreal transplantation in a rat model of chronic ocular hypertension (COH).
COH was induced by laser cauterization of trabecular meshwork and episcleral veins in rat eyes. COH eyes received an intravitreal transplant of MSCs engineered to express BDNF and green fluorescent protein (BDNF-MSCs) or just GFP (GFP-MSCs). Computerized pupillometry and electroretinography (ERG) were performed to assess optic nerve and retinal function. Quantification of optic nerve damage was performed by counting retinal ganglion cells (RGCs) and evaluating optic nerve cross-sections.
After transplantation into COH eyes, BDNF-MSCs preserved significantly more retina and optic nerve function than GFP-MSC–treated eyes when pupil light reflex (PLR) and ERG function were evaluated. PLR analysis showed significantly better function (P = 0.03) in BDNF-MSC–treated eyes (operated/control ratio = 63.00% ± 11.39%) than GFP-MSC–treated eyes (operated/control ratio = 31.81% ± 9.63%) at 42 days after surgery. The BDNF-MSC–transplanted eyes also displayed a greater level of RGC preservation than eyes that received the GFP-MSCs only (RGC cell counts: BDNF-MSC–treated COH eyes, 112.2 ± 19.39 cells/section; GFP-MSC–treated COH eyes, 52.21 ± 11.54 cells/section; P = 0.01).
The authors have demonstrated that lentiviral-transduced BDNF-producing MSCs can survive in eyes with chronic hypertension and can provide retina and optic nerve functional and structural protection. Transplantation of BDNF-producing stem cells may be a viable treatment strategy for glaucoma.
Polycystin-1 (PC1) is a large, membrane-bound protein that localizes to the cilia and is implicated in the common ciliopathy autosomal-dominant polycystic kidney disease. The physiological function of PC1 is dependent upon its subcellular localization as well as specific cleavages that release soluble fragments of its C-terminal tail. The techniques described here allow visualization and quantification of these aspects of the biology of the PC1 protein. To visualize PC1 at the plasma membrane, a live-cell surface labeling immunofluorescence protocol paired with the labeling of an internal antigen motif allows a robust detection of the surface population of this protein. This technique is modified to generate a surface enzyme-linked immunosorbent assay (ELISA), which quantitatively measures the amount of surface protein as a fraction of the total amount of the protein expressed in that cell population. These assays are powerful tools in the assessment of the small but biologically important pool of PC1 that reaches the cell surface. The C-terminal tail cleavage of PC1 constitutes an interesting modification that allows PC1 to extend its functional role into the nucleus. A reporter assay based on Gal4/VP16 luciferase can be used to quantitate the amount of PC1 C-terminal tail that reaches the nucleus. This assay can be paired with quantitative measurement of the protein expression in the cell, allowing a more complete understanding of the pattern of PC1 cleavage and the nuclear localization of the resultant.
The responses of adult parasympathetic ganglion neurons to injury and the neurotrophic mechanisms underlying their axonal regeneration are poorly understood. This is especially relevant to penis-projecting parasympathetic neurons, which are vulnerable to injury during pelvic surgery such as prostatectomy. We investigated the changes in pelvic ganglia of adult male rats in the first week after unilateral cavernous (penile) nerve axotomy (cut or crush lesions). In some experiments FluoroGold was injected into the penis seven days prior to injury to allow later identification of penis-projecting neurons. Neurturin and glial cell line-derived neurotrophic factor (GDNF) are neurotrophic factors for penile parasympathetic neurons, so we also examined expression of relevant receptors, GFRα1 and GFRα2, in injured pelvic ganglion neurons.
Axotomy caused prolific growth of axon collaterals (sprouting) in pelvic ganglia ipsilateral to the injury. These collaterals were most prevalent in the region near the exit of the penile nerve. This region contained the majority of FluoroGold-labelled neurons. Many sprouting fibres formed close associations with sympathetic and parasympathetic pelvic neurons, including many FluoroGold neurons. However immunoreactivity for synaptic proteins could not be demonstrated in these collaterals. Preganglionic terminals showed a marked loss of synaptic proteins, suggesting a retrograde effect of the injury beyond the injured neurons. GFRα2 immunofluorescence intensity was decreased in the cytoplasm of parasympathetic neurons, but GFRα1 immunofluorescence was unaffected in these neurons.
These studies show that there are profound changes within the pelvic ganglion after penile nerve injury. Sprouting of injured postganglionic axons occurs concurrently with structural or chemical changes in preganglionic terminals. New growth of postganglionic axon collaterals within the ganglion raises the possibility of the formation of aberrant synaptic connections between injured and un-injured ganglion neurons. Together these changes demonstrate a broader effect on the pelvic autonomic circuitry than simply loss of neuroeffector connections. These structural changes are accompanied by potential changes in neurotrophic factor signalling due to altered expression of receptors for members of the GDNF family. Together our results advance understanding of the responses of pelvic autonomic nerve circuits to injury and may assist in designing strategies for promoting regeneration.
Erythropoietin (EPO) may be protective for early stage diabetic retinopathy, although there are concerns that it could exacerbate retinal angiogenesis and thrombosis. A peptide based on the EPO helix-B domain (helix B-surface peptide [pHBSP]) is nonerythrogenic but retains tissue-protective properties, and this study evaluates its therapeutic potential in diabetic retinopathy.
RESEARCH DESIGN AND METHODS
After 6 months of streptozotocin-induced diabetes, rats (n = 12) and age-matched nondiabetic controls (n = 12) were evenly split into pHBSP and scrambled peptide groups and injected daily (10 μg/kg per day) for 1 month. The retina was investigated for glial dysfunction, microglial activation, and neuronal DNA damage. The vasculature was dual stained with isolectin and collagen IV. Retinal cytokine expression was quantified using real-time RT-PCR. In parallel, oxygen-induced retinopathy (OIR) was used to evaluate the effects of pHBSP on retinal ischemia and neovascularization (1–30 μg/kg pHBSP or control peptide).
pHBSP or scrambled peptide treatment did not alter hematocrit. In the diabetic retina, Müller glial expression of glial fibrillary acidic protein was increased when compared with nondiabetic controls, but pHBSP significantly reduced this stress-related response (P < 0.001). CD11b+ microglia and proinflammatory cytokines were elevated in diabetic retina responses, and some of these responses were attenuated by pHBSP (P < 0.01–0.001). pHBSP significantly reduced diabetes-linked DNA damage as determined by 8-hydroxydeoxyguanosine and transferase-mediated dUTP nick-end labeling positivity and also prevented acellular capillary formation (P < 0.05). In OIR, pHBSP had no effect on preretinal neovascularization at any dose.
Treatment with an EPO-derived peptide after diabetes is fully established can significantly protect against neuroglial and vascular degenerative pathology without altering hematocrit or exacerbating neovascularization. These findings have therapeutic implications for disorders such as diabetic retinopathy.
Neurotrophic factors are playing vital roles in survival, growth, and function of neurons. Regulation of neurotrophic factors in the brain has been considered as one of the targets in developing drug or therapy against neuronal disorders. Flavonoids, a family of multifunctional natural compounds, are well known for their neuronal beneficial effects. Here, the effects of flavonoids on regulating neurotrophic factors were analyzed in cultured rat astrocytes. Astrocyte is a major secreting source of neurotrophic factors in the brain. Thirty-three flavonoids were screened in the cultures, and calycosin, isorhamnetin, luteolin, and genistein were identified to be highly active in inducing the synthesis and secretion of neurotrophic factors, including nerve growth factor (NGF), glial-derived neurotrophic factor (GDNF), and brain-derived neurotrophic factor (BDNF). The inductions were in time- and dose-dependent manners. In cultured astrocytes, the phosphorylation of estrogen receptor was triggered by application of flavonoids. The phosphorylation was blocked by an inhibitor of estrogen receptor, which in parallel reduced the flavonoid-induced expression of neurotrophic factors. The results proposed the role of flavonoids in protecting brain diseases, and therefore these flavonoids could be developed for health food supplement for patients suffering from neurodegenerative diseases.
Mesencephalic astrocyte-derived neurotrophic factor (MANF), a 20 kDa secreted protein, was originally derived from a rat mesencephalic type-1 astrocyte cell line. MANF belongs to a novel evolutionally conserved family of neurotrophic factors along with conserved dopamine neurotrophic factor. In recent years, ever-increasing evidence has shown that both of them play a remarkable protective role against various injuries to neurons in vivo or in vitro. However, the characteristics of MANF expression in the different types of glial cells, especially in astrocytes, remain unclear.
The model of focal cerebral ischemia was induced by rat middle cerebral artery occlusion. Double-labeled immunofluorescent staining was used to identify the types of neural cells expressing MANF. Primarily cultured glial cells were used to detect the response of glial cells to endoplasmic reticulum stress stimulation. Propidium iodide staining was used to determine dead cells. Reverse transcription PCR and western blotting were used to detect the levels of mRNA and proteins.
We found that MANF was predominantly expressed in neurons in both normal and ischemic cortex. Despite its name, MANF was poorly expressed in glial cells, including astrocytes, in normal brain tissue. However, the expression of MANF was upregulated in the glial cells under focal cerebral ischemia, including the astrocytes. This expression was also induced by several endoplasmic reticulum stress inducers and nutrient deprivation in cultured primary glial cells. The most interesting phenomenon observed in this study was the pattern of MANF expression in the microglia. The expression of MANF was closely associated with the morphology and state of microglia, accompanied by the upregulation of BIP/Grp78.
These results indicate that MANF expression was upregulated in the activated glial cells, which may contribute to the mechanism of ischemia-induced neural injury.
Mesencephalic astrocyte-derived neurotrophic factor; Endoplasmic reticulum stress; Glial activation; Cerebral ischemia