PMCC PMCC

Search tips
Search criteria

Advanced
Results 1-24 (24)
 

Clipboard (0)
None

Select a Filter Below

Year of Publication
1.  Aminothienopyridazine inhibitors of tau aggregation: Evaluation of structure–activity relationship leads to selection of candidates with desirable in vivo properties 
Bioorganic & medicinal chemistry  2012;20(14):4451-4461.
Previous studies demonstrated that members of the aminothienopyridazine (ATPZ) class of tau aggregation inhibitors exhibit a promising combination of in vitro activity as well as favorable pharmacokinetic properties (i.e., brain-penetration and oral bioavailability). Here we report the synthesis and evaluation of several new analogues. These studies indicate that the thienopyridazine core is essential for inhibition of tau fibrillization in vitro, while the choice of the appropriate scaffold decoration is critical to impart desirable ADME-PK properties. Among the active, brain-penetrant ATPZ inhibitors evaluated, 5-amino-N-cyclopropyl-3-(4-fluorophenyl)-4-oxo-3,4-dihydrothieno[3,4-d]pyridazine-1-carboxamide (43) was selected to undergo maximum tolerated dose and one-month tolerability testing in mice. The latter studies revealed that this compound is well-tolerated with no notable side-effects at an oral dose of 50 mg/kg/day.
doi:10.1016/j.bmc.2012.05.027
PMCID: PMC4304654  PMID: 22717239
Alzheimer’s disease; Tauopathy; Aminothienopyridazine; Tau aggregation inhibitor; K18PL
2.  Intracerebral injection of preformed synthetic tau fibrils initiates widespread tauopathy and neuronal loss in the brains of tau transgenic mice 
Neurobiology of disease  2014;73:83-95.
Neurofibrillary tangles composed of hyperphosphorylated fibrillized tau are found in numerous tauopathies including Alzheimer's disease. Increasing evidence suggests that tau pathology can be transmitted from cell-to-cell; however the mechanisms involved in the initiation of tau fibrillization and spreading of disease linked to progression of tau pathology are poorly understood. We show here that intracerebral injections of preformed synthetic tau fibrils into the hippocampus or frontal cortex of young tau transgenic mice expressing mutant human P301L tau induces tau hyperphosphorylation and aggregation around the site of injection, as well as a time-dependent propagation of tau pathology to interconnected brain areas distant from the injection site. Furthermore, we show that the tau pathology as a consequence of injection of tau preformed fibrils into the hippocampus induces selective loss of CA1 neurons. Together, our data confirm previous studies on the seeded induction and the spreading of tau pathology in a different tau transgenic mouse model and reveals neuronal loss associated with seeded tau pathology in tau transgenic mouse brain. These results further validate the utility of the tau seeding model in studying disease transmission, and provide a more complete in vivo tauopathy model with associated neurodegeneration which can be used to investigate the mechanisms involved in tau aggregation and spreading, as well as aid in the search for disease modifying treatments for Alzheimer's disease and related tauopathies.
doi:10.1016/j.nbd.2014.08.032
PMCID: PMC4303592  PMID: 25220759
Seeding; Spreading; Tau pathology; Cell death
3.  The microtubule-stabilizing agent, epothilone D, reduces axonal dysfunction, neurotoxicity, cognitive deficits and Alzheimer-like pathology in an interventional study with aged tau transgenic mice 
The Journal of Neuroscience  2012;32(11):3601-3611.
Neurodegenerative tauopathies, such as Alzheimer’s disease (AD), are characterized by insoluble deposits of hyperphosphorylated tau protein within brain neurons. Increased phosphorylation and decreased solubility has been proposed to diminish normal tau stabilization of microtubules (MTs), thereby leading to neuronal dysfunction. Earlier studies have provided evidence that small molecule MT-stabilizing drugs that are used in the treatment of cancer may have utility in the treatment of tauopathies. However, it has not been established whether treatment with a small molecule MT-stabilizing compound will provide benefit in a Tg model with pre-existing tau pathology, as would be seen in human patients with clinical symptoms. Accordingly, we describe here an interventional study of the brain-penetrant MT-stabilizing agent, epothilone D (EpoD), in aged PS19 mice with existing tau pathology and related behavioral deficits. EpoD treatment reduced axonal dystrophy and increased axonal MT density in the aged PS19 mice, which led to improved fast axonal transport and cognitive performance. Moreover, the EpoD-treated PS19 mice had less forebrain tau pathology and increased hippocampal neuronal integrity, with no dose-limiting side effects. These data reveal that brain-penetrant MT-stabilizing drugs hold promise for the treatment of AD and related tauopathies, and that EpoD could be a candidate for clinical testing.
doi:10.1523/JNEUROSCI.4922-11.2012
PMCID: PMC3321513  PMID: 22423084
4.  MT-Stabilizer, Dictyostatin, Exhibits Prolonged Brain Retention and Activity: Potential Therapeutic Implications 
ACS Medicinal Chemistry Letters  2013;4(9):886-889.
Inclusions comprising the microtubule (MT)-stabilizing protein, tau, are found within neurons in the brains of patients with Alzheimer’s disease and related neurodegenerative disorders that are broadly referred to as tauopathies. The sequestration of tau into inclusions is believed to cause a loss of tau function, such that MT structure and function are compromised, leading to neuronal damage. Recent data reveal that the brain-penetrant MT-stabilizing agent, epothilone D (EpoD), improves cognitive function and decreases both neuron loss and tau pathology in transgenic mouse models of tauopathy. There is thus a need to identify additional MT-stabilizing compounds with blood–brain barrier (BBB) permeability and slow brain clearance, as observed with EpoD. We report here that the MT-stabilizing natural product, dictyostatin, crosses the BBB in mice and has extended brain retention. Moreover, a single administration of dictyostatin to mice causes prolonged stabilization of MTs in the brain. In contrast, the structurally related MT-stabilizer, discodermolide, shows significantly less brain exposure. Thus, dictyostatin merits further investigation as a potential tauopathy therapeutic.
doi:10.1021/ml400233e
PMCID: PMC4027543  PMID: 24900764
Blood−brain barrier; discodermolide; dictyostatin; microtubule; pharmacokinetics; tauopathy
5.  The Characterization of Microtubule-Stabilizing Drugs as Possible Therapeutic Agents for Alzheimer’s Disease and Related Tauopathies 
Tau, a protein that is enriched in neurons of the central nervous system (CNS)1, is thought to play a critical role in the stabilization of microtubules (MTs). Several neurodegenerative disorders referred to as tauopathies, including Alzheimer’s disease and certain types of frontotemporal lobar degeneration, are characterized by the intracellular accumulation of hyperphosphorylated tau fibrils. Tau deposition into insoluble aggregates is believed to result in a loss of tau function that leads to MT destabilization, and this could cause neurodegeneration as intact MTs are required for axonal transport and normal neuron function. This tau loss-of-function hypothesis has been validated in a tau transgenic mouse model with spinal cord tau inclusions, where the MT-stabilizing agent, paclitaxel, increased spinal nerve MT density and improved motor function after drug absorption at neuromuscular junctions. Unfortunately, paclitaxel is a P-glycoprotein substrate and has poor blood-brain barrier permeability, making it unsuitable for the treatment of human tauopathies. We therefore examined several MT-stabilizing compounds from the taxane and epothilone natural product families to assess their membrane permeability and to determine whether they act as substrates or inhibitors of P-glycoprotein. Moreover, we compared brain and plasma levels of the compounds after administration to mice. Finally, we assessed whether brain-penetrant compounds could stabilize mouse CNS MTs. We found that several epothilones have significantly greater brain penetration than the taxanes. Furthermore, certain epothilones cause an increase in CNS MT stabilization, with epothilone D demonstrating a favorable pharmacokinetic and pharmacodynamic profile which suggests this agent merits further study as a potential tauopathy drug candidate.
doi:10.1016/j.phrs.2010.12.002
PMCID: PMC3042036  PMID: 21163349
Alzheimer’s disease; microtubules; tauopathies; therapeutic
6.  Epothilone D Improves Microtubule Density, Axonal Integrity and Cognition in a Transgenic Mouse Model of Tauopathy 
Neurons in the brains of those with Alzheimer's disease (AD) and many frontotemporal dementias (FTDs) contain neurofibrillary tangles (NFTs) comprised of hyperphosphorylated tau protein. Tau normally stabilizes microtubules (MTs), and tau misfolding could lead to a loss of this function with consequent MT destabilization and neuronal dysfunction. Accordingly, a possible therapeutic strategy for AD and related “tauopathies” is treatment with a MT-stabilizing anti-cancer drug such as paclitaxel. However, paclitaxel and related taxanes have poor blood-brain barrier permeability and thus are unsuitable for diseases of the brain. We demonstrate here that the MT-stabilizing agent, epothilone D (epoD), is brain-penetrant and we subsequently evaluated whether epoD can compensate for tau loss-of-function in PS19 tau Tg mice that develop forebrain tau inclusions, axonal degeneration and MT deficits. Treatment of 3-month old male PS19 mice with low doses of epoD once-weekly for a 3-month period significantly improved CNS MT density and axonal integrity without inducing notable side-effects. Moreover, epoD treatment reduced cognitive deficits that were observed in the PS19 mice. These results suggest that certain brain-penetrant MT-stabilizing agents might provide a viable therapeutic strategy for the treatment of AD and FTDs.
doi:10.1523/JNEUROSCI.3059-10.2010
PMCID: PMC2958430  PMID: 20943926
Tau; Microtubule; Blood-brain barrier; Alzheimer's disease; Learning and Memory; Transgenic
7.  The Identification of Aminothienopyridazine Inhibitors of Tau Assembly by Quantitative High-Throughput Screening† 
Biochemistry  2009;48(32):7732-7745.
Inclusions comprised of fibrils of the microtubule (MT)-associated protein tau are found in the brains of those with Alzheimer’s disease (AD) and other neurodegenerative tauopathies. The pathology that is observed in these diseases is believed to result from the formation of toxic tau oligomers or fibrils, and/or from the loss of normal tau function due to its sequestration into insoluble deposits. Hence, small molecules that prevent tau oligomerization and/or fibrillization might have therapeutic value. Indeed, examples of such compounds have been published but nearly all have properties that render them unsuitable as drug candidates. For these reasons, we conducted quantitative high-throughput screening (qHTS) of ~292,000 compounds to identify drug-like inhibitors of tau assembly. The fibrillization of a truncated tau fragment that contains four MT-binding domains was monitored in an assay that employed complementary thioflavine T fluorescence and fluorescence polarization methods. Previously described classes of inhibitors as well as new scaffolds were identified, including novel aminothienopyridazines (ATPZ’s). A number of ATPZ analogs were synthesized and structure-activity relationships were defined. Further characterization of representative ATPZ compounds showed they do not interfere with tau-mediated MT assembly, and they are significantly more effective at preventing the fibrillization of tau than the Aβ(1–42) peptide which forms AD senile plaques. Thus, the ATPZ molecules described here represent a novel class of tau assembly inhibitors that merit further development for testing in animal models of AD-like tau pathology.
doi:10.1021/bi9006435
PMCID: PMC2773749  PMID: 19580328
8.  Brain-Penetrant Tetrahydronaphthalene Thromboxane A2-Prostanoid (TP) Receptor Antagonists as Prototype Therapeutics for Alzheimer’s Disease 
ACS Chemical Neuroscience  2012;3(11):928-940.
A hallmark pathological feature of the Alzheimer’s disease (AD) brain is the presence of senile plaques, which comprise amyloid β (Aβ) peptides that are derived from the amyloid precursor protein (APP). The plaque-containing AD brain is thought to be under oxidative stress, as evidenced by increased lipid oxidation products that include isoprostane-F2αIII (iPF2αIII). IPF2αIII can bind to and activate the thromboxane A2-prostanoid (TP) receptor, and TP receptor activation causes increased Aβ production through enhancement of APP mRNA stability. Moreover, TP receptor antagonists have been shown to block iPF2αIII-induced increases of Aβ secretion. Thus, the TP receptor may be a potential drug target for AD therapy. However, here we show that existing TP receptor antagonists have poor blood-brain barrier (BBB) permeability, likely due to the presence of a carboxylic acid moiety that is believed to be important for receptor interaction, but which may hamper passive diffusion across the BBB. We now report selected analogues of a known tetrahydronaphthalene TP receptor antagonist, wherein the carboxylic acid moiety has been replaced by heterocyclic bioisosteres. These heterocyclic analogues retained relatively high affinity for the mouse and human TP receptors, and, unlike the parent carboxylic acid compound, several examples freely diffused across the BBB into the brain upon administration to mice. These results reveal that brain-penetrant tetrahydronaphthalene TP receptor antagonists can be developed by substituting the carboxylic acid moiety with a suitable nonacidic bioisostere. Compounds of this type hold promise as potential lead structures to develop drug candidates for the treatment of AD.
doi:10.1021/cn3000795
PMCID: PMC3503350  PMID: 23173073
Alzheimer’s disease; amyloid precursor protein; antagonist; blood-brain barrier; plaques; thromboxane receptor
9.  Microtubule Stabilizing Agents as Potential Treatment for Alzheimer’s Disease and Related Neurodegenerative Tauopathies 
Journal of medicinal chemistry  2012;55(21):8979-8996.
The microtubule (MT)-associated protein tau, which is highly expressed in the axons of neurons, is an endogenous MT-stabilizing agent that plays an important role in the axonal transport. Loss of MT-stabilizing tau function, caused by misfolding, hyperphosphorylation and sequestration of tau into insoluble aggregates, leads to axonal transport deficits with neuropathological consequences. Several in vitro and preclinical in vivo studies have shown that MT-stabilizing drugs can be utilized to compensate for the loss of tau function and to maintain/restore an effective axonal transport. These findings indicate that MT-stabilizing compounds hold considerable promise for the treatment of Alzheimer disease and related tauopathies. The present article provides a synopsis of the key findings demonstrating the therapeutic potential of MT-stabilizing drugs in the context of neurodegenerative tauopathies, as well as an overview of the different classes of MT-stabilizing compounds.
doi:10.1021/jm301079z
PMCID: PMC3493881  PMID: 23020671
11.  Brain-penetrant microtubule-stabilizing compounds as potential therapeutic agents for tauopathies 
Biochemical Society transactions  2012;40(4):661-666.
Neurons within the brains of those with AD (Alzheimer’s disease) and related neurodegenerative disorders, collectively termed ‘tauopathies’, contain fibrillar inclusions composed of hyperphosphorylated tau protein. Tau is normally enriched in axons, where it binds and stabilizes MTs (microtubules). Tau hyperphosphorylation and aggregation probably result in reduced MT binding that could affect axonal transport and neuronal function. A possible therapeutic strategy to overcome a loss of tau function in tauopathies is administration of MT-stabilizing agents, such as those used in the treatment of cancer. However, these drugs elicit severe side effects, and most existing MT-stabilizing compounds have poor BBB (blood–brain barrier) permeability, which renders them unsuitable for tauopathy treatment. We identified EpoD (epothilone D) as a brain-penetrant MT-stabilizing agent with preferred pharmacokinetic and pharmacodynamic properties. EpoD was evaluated for its ability to compensate for tau loss-of-function in an established Tg (transgenic) mouse model, using both preventative and interventional dosing paradigms. EpoD at doses much lower than previously used in human cancer patients caused improved axonal MT density and decreased axonal dystrophy in the tau Tg mice, leading to an alleviation of cognitive deficits. Moreover, EpoD reduced the extent of tau pathology in aged tau Tg mice. Importantly, no adverse side effects were observed in the EpoD-treated mice. These results suggest that EpoD might be a viable drug candidate for the treatment of AD and related tauopathies.
doi:10.1042/BST20120010
PMCID: PMC3431553  PMID: 22817712
Alzheimer’s disease; axon; microtubule; tauopathy; therapeutic agent
12.  Response to Comments on “ApoE-Directed Therapeutics Rapidly Clear β-Amyloid and Reverse Deficits in AD Mouse Models” 
Science (New York, N.Y.)  2013;340(6135):924-92g.
The data reported in the Technical Comments by Fitz et al., Price et al., Tesseur et al., and Veeraraghavalu et al. replicate and validate our central conclusion that bexarotene stimulates the clearance of soluble β-amyloid peptides and results in the reversal of behavioral deficits in mouse models of Alzheimer’s disease (AD). The basis of the inability to reproduce the drug-stimulated microglial-mediated reduction in plaque burden is unexplained. However, we concluded that plaque burden is functionally unrelated to improved cognition and memory elicited by bexarotene.
doi:10.1126/science.1234114
PMCID: PMC3714602  PMID: 23704556
13.  ApoE-Directed Therapeutics Rapidly Clear β-Amyloid and Reverse Deficits in AD Mouse Models 
Science (New York, N.Y.)  2012;335(6075):1503-1506.
Alzheimer’s disease (AD) is associated with impaired clearance of β-amyloid (Aβ) from the brain, a process normally facilitated by apolipoprotein E (apoE). ApoE expression is transcriptionally induced through the action of the nuclear receptors peroxisome proliferator–activated receptor gamma and liver X receptors in coordination with retinoid X receptors (RXRs). Oral administration of the RXR agonist bexarotene to a mouse model of AD resulted in enhanced clearance of soluble Aβ within hours in an apoE-dependent manner. Aβ plaque area was reduced more than 50% within just 72 hours. Furthermore, bexarotene stimulated the rapid reversal of cognitive, social, and olfactory deficits and improved neural circuit function. Thus, RXR activation stimulates physiological Aβ clearance mechanisms, resulting in the rapid reversal of a broad range of Aβ-induced deficits.
doi:10.1126/science.1217697
PMCID: PMC3651582  PMID: 22323736
14.  Cyclopentane-1,3-dione: A Novel Isostere for the Carboxylic Acid Functional Group. Application to the Design of Potent Thromboxane (A2)-Receptor Antagonists 
Journal of medicinal chemistry  2011;54(19):6969-6983.
Cyclopentane-1,3-diones are known to exhibit pKa values typically in the range of carboxylic acids. To explore the potential of the cyclopentane-1,3-dione unit as a carboxylic acid isostere, the physical-chemical properties of representative congeners were examined and compared with similar derivatives bearing carboxylic acid or tetrazole residues. These studies suggested that cyclopentane-1,3-diones may effectively substitute for the carboxylic acid functional group. To demonstrate the use of the cyclopentane-1,3-dione isostere in drug-design, derivatives of a known thromboxane-A2 prostanoid (TP) receptor antagonist, 3-(3-(2-(4-chlorophenylsulfonamido)ethyl)-phenyl)propanoic acid (12), were synthesized and evaluated in both functional and radioligand-binding assays. A series of mono- and di-substituted cyclopentane-1,3-dione derivatives (41–45) were identified that exhibit nM IC50 and Kd values similar to 12. Collectively, these studies demonstrate that the cyclopentane-1,3-dione moiety comprises a novel isostere of the carboxylic acid functional group. Given the combination of the relatively strong acidity, tunable lipophilicity, and versatility of the structure, the cyclopentane-1,3-dione moiety may constitute a valuable addition to the palette of carboxylic acid isosteres.
doi:10.1021/jm200980u
PMCID: PMC3188681  PMID: 21863799
isostere; bio-isostere; TP receptor; antagonist; cyclopentane-1,3-dione
15.  Chronic stress exacerbates tau pathology, neurodegeneration, and cognitive performance through a corticotropin-releasing factor receptor-dependent mechanism in a transgenic mouse model of tauopathy 
Since over-activation of the hypothalamic-pituitary-adrenal (HPA) axis occurs in Alzheimer’s disease (AD), dysregulation of stress neuromediators may play a mechanistic role in the pathophysiology of AD. However, the effects of stress on tau phosphorylation are poorly understood and the relationship between corticosterone and corticotropin-releasing factor (CRF) on both Aβ and tau pathology remain unclear. Therefore, we first established a model of chronic stress which exacerbates Aβ accumulation in Tg2576 mice and then extended this stress paradigm to a tau transgenic mouse model with the P301S mutation (PS19) which displays tau hyperphosphorylation, insoluble tau inclusions and neurodegeneration. We show for the first time that both Tg2576 and PS19 mice demonstrate a heightened HPA stress profile in the unstressed state. In Tg2576 mice, one month of restraint/isolation (RI) stress increased Aβ levels, suppressed microglial activation, and worsened spatial and fear memory compared to non-stressed mice. In PS19 mice, RI stress promoted tau hyperphosphorylation, insoluble tau aggregation, neurodegeneration and fear-memory impairments. These effects were not mimicked by chronic corticosterone administration but were prevented by pre-stress administration of a CRF receptor type 1 (CRF1) antagonist. The role for a CRF1-dependent mechanism was further supported by the finding that mice over-expressing CRF had increased hyperphosphorylated tau compared to wildtype littermates. Together, these results implicate HPA dysregulation in AD neuropathogenesis and suggest that prolonged stress may increase Aβ and tau hyperphosphorylation. These studies also implicate CRF in AD pathophysiology and suggest that pharmacological manipulation of this neuropeptide may be a potential therapeutic strategy for AD.
doi:10.1523/JNEUROSCI.3836-11.2011
PMCID: PMC3230070  PMID: 21976528
stress; corticosterone; corticotropin-releasing factor; hypothalamic-pituitary-adrenal axis; Alzheimer’s disease; β-amyloid; tau
16.  Developing Therapeutic Approaches to Tau, Selected Kinases, and Related Neuronal Protein Targets 
A hallmark of the Alzheimer disease (AD) brain is the presence of inclusions within neurons that are comprised of fibrils formed from the microtubule-stabilizing protein tau. The formation of misfolded multimeric tau species is believed to contribute to the progressive neuron loss and cognitive impairments of AD. Moreover, mutations in tau have been shown to cause a form of frontotemporal lobar degeneration in which tau neuronal inclusions observed in the brain are similar to those seen in AD. Here we review the more compelling strategies that are designed to reduce the contribution of misfolded tau to AD neuropathology, including those directed at correcting a possible loss of tau function resulting from sequestration of cellular tau and to minimizing possible gain-of-function toxicities caused by multimeric tau species. Finally, we discuss the challenges and potential benefits of tau-directed drug discovery programs.
Neurodegeneration in Alzheimer disease is likely caused by misfolded, multimeric tau. Therapeutic strategies have focused on overcoming tau loss-of-function and reducing levels of potentially toxic tau species.
doi:10.1101/cshperspect.a006437
PMCID: PMC3234455  PMID: 22229117
17.  Tau-Directed Drug Discovery for Alzheimer’s Disease and Related Tauopathies: A Focus on Tau Assembly Inhibitors 
Experimental neurology  2009;223(2):304-310.
The microtubule-associated protein tau forms insoluble filaments that deposit as neurofibrillary tangles (NFTs) in the brains of those with Alzheimer’s disease (AD) and other related neurodegenerative disorders. The presence of both NFTs and amyloid β (Aβ)-containing senile plaques within the brain is required to confirm the diagnosis of AD. However, the demonstration that familial AD can be caused by mutations that result in increased Aβ production has resulted in AD drug discovery strategies that are largely focused on reducing brain Aβ levels, with substantially less emphasis on tau-directed approaches. This trend may be changing, as there are an increasing number of research programs that are exploring ways to reduce NFTs in AD and related tauopathies. We briefly review recent advances in tau-based drug discovery, with an emphasis on the identification of compounds that inhibit the assembly of tau into multimers and fibrils.
doi:10.1016/j.expneurol.2009.08.031
PMCID: PMC2864354  PMID: 19744482
18.  Discovery of Brain-Penetrant, Orally Bioavailable Aminothienopyridazine Inhibitors of Tau Aggregation 
Journal of medicinal chemistry  2010;53(9):3739-3747.
Agents capable of preventing the misfolding and sequestration of the microtubule-stabilizing protein tau into insoluble fibrillar aggregates hold considerable promise for the prevention and/or treatment of neurodegenerative tauopathies such as Alzheimer’s disease. Because tauopathies are characterized by amyloidosis that is restricted to the central nervous system (CNS), plausible candidate compounds for in vivo evaluation must both prevent tau fibrillization and achieve significant brain levels. Recently, we reported the discovery of the aminothienopyridazine (ATPZ) class of tau aggregation inhibitors and now describe a series of new analogues that are both effective inhibitors of tau fibrillization and display significant brain-to-plasma exposure ratios after administration to mice. Further, two of the most promising examples, 15 and 16, were found to reach significant brain exposure levels following oral administration. Taken together, these results suggest that examples from the ATPZ class hold promise as candidates for in vivo efficacy studies in animal models of neurodegenerative tauopathies.
doi:10.1021/jm100138f
PMCID: PMC2872922  PMID: 20392114
aminothienopyridazine; tauopathy; Alzheimer’s disease; amyloid; tau-aggregation inhibitor
19.  Characterization of tau fibrillization in vitro 
Background
The assembly of tau proteins into paired helical filaments, the building blocks of neurofibrillary tangles, is linked to neurodegeneration in Alzheimer’s disease and related tauopathies. A greater understanding of this assembly process could identify targets for the discovery of drugs to treat Alzheimer’s disease and related disorders. Using recombinant human tau, we have delineated events leading to the conversion of normal soluble tau into tau fibrils
Methods
Atomic force microscopy and transmission electron microscopy methodologies were utilized to determine the structure of tau assemblies that formed when soluble tau was incubated with heparin for increasing lengths of time.
Results
Tau initially oligomerizes into spherical nucleation units of 18–21 nm diameter that appear to assemble linearly into nascent fibrils. Among the earliest tau fibrils are species that resemble a string of beads formed by linearly aligned spheres that with time seem to coalesce to form straight and twisted ribbon-like filaments, as well as paired-helical filaments similar to those found in human tauopathies. An analysis of fibril cross-sections at later incubation times revealed three fundamental axial structural features.
Conclusions
By monitoring tau fibrillization, we show that different tau filament morphologies co-exist. Temporal changes in the predominant tau structural species suggest that tau fibrillization involves the generation of structural intermediates, resulting in the formation of tau fibrils with verisimilitude to their authentic human counterparts.
doi:10.1016/j.jalz.2009.06.002
PMCID: PMC2842604  PMID: 20298971
Alzheimer’s disease; tauopathy; amyloid; tangles; neurodegeneration
20.  Advances in Tau-focused drug discovery for Alzheimer's disease and related tauopathies 
Nature reviews. Drug discovery  2009;8(10):783-793.
Preface
Neuronal inclusions comprised of the microtubule-associated protein tau are found in a number of neurodegenerative diseases, commonly known as tauopathies. In Alzheimer's disease, the most prevalent tauopathy, misfolded tau is probably a key pathological agent. The recent failure of Aβ-targeted therapeutics in Phase III clinical trials suggests that it is timely and prudent to consider alternative drug discovery strategies for Alzheimer's disease. Here we focus on those directed at reducing misfolded tau and compensating for the loss of normal tau function.
doi:10.1038/nrd2959
PMCID: PMC2787232  PMID: 19794442
21.  Evidence That Non-Fibrillar Tau Causes Pathology Linked To Neurodegeneration And Behavioral Impairments 
The discovery that mutations within the tau gene lead to frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17) provided direct evidence that tau alterations can lead to neurodegenerative disease. While the presence of tau fibrils and tangles is a common feature of all tauopathies, including Alzheimer’s disease (AD), data are emerging from biochemical, cell-based and transgenic mouse studies which suggest that a pre-fibrillar form of pathological tau may play a key role in eliciting central nervous system (CNS) neurodegeneration and behavioral impairments. Herein we review recent findings that implicate diffusible tau pathology in the onset of neurodegeneration, and discuss the implications of these findings as they relate to tau tangles and possible therapeutic strategies for the treatment of AD and related tauopathies.
PMCID: PMC2789426  PMID: 18688089
Fibrils; Neurodegeneration; Oligomers; Tangles; Tau; Transgenic
22.  Effects of TACE inhibition on Amyloid β production and APP processing in vitro and in vivo 
TNFα is a pro-inflammatory cytokine that is elevated in Alzheimer’s disease (AD) brains. Since TNFα is released from cell membranes by the TNFα converting enzyme (TACE), inhibition of TACE has the potential to mitigate TNFα effects in AD brain. TACE also cleaves amyloid precursor protein (APP) and generates sAPPα, precluding the formation of potentially harmful Aβ peptides by β-site APP cleaving enzymes (BACE). Hence, the anti-inflammatory benefits of TACE inhibition might be offset by an increase in Aβ. We have examined the effects of the highly selective TACE inhibitor, BMS-561392, on APP processing in vitro and in vivo. In CHO cells expressing APP, BMS-561392 significantly reduced secretion of sAPPα without a corresponding increase in Aβ production. Conversely, a BACE inhibitor decreased sAPPβ and Aβ peptides with no change in the secretion of sAPPα. These data indicate an absence of TACE and BACE competition for the APP substrate. Despite this, we observed competition for APP when TACE activity was enhanced via phorbol ester treatment or if APP was modified such that it was retained within the trans Golgi network (TGN). These results suggest that BACE and TACE share a common TGN localization, but under normal conditions do not compete for APP. To confirm this finding in vivo, BMS-561392 was infused into the brains of Tg2576 and wild-type mice. While decreased brain sAPPα levels were observed, steady-state Aβ levels were not significantly changed. Accordingly, it is possible that TACE inhibitors could reduce TNFα levels without increasing Aβ levels within the AD brain.
doi:10.1523/JNEUROSCI.2913-08.2008
PMCID: PMC2646261  PMID: 19005070
Alzheimer’s disease; amyloid-beta; inflammation; neuroinflammation; tumor necrosis factor; TNFα
23.  GPRC6A Null Mice Exhibit Osteopenia, Feminization and Metabolic Syndrome 
PLoS ONE  2008;3(12):e3858.
Background
GPRC6A is a widely expressed orphan G-protein coupled receptor that senses extracellular amino acids, osteocalcin and divalent cations in vitro. The physiological functions of GPRC6A are unknown.
Methods/Principal Findings
In this study, we created and characterized the phenotype of GPRC6A−/− mice. We observed complex metabolic abnormalities in GPRC6A−/− mice involving multiple organ systems that express GPRC6A, including bone, kidney, testes, and liver. GPRC6A−/− mice exhibited hepatic steatosis, hyperglycemia, glucose intolerance, and insulin resistance. In addition, we observed high expression of GPRC6A in Leydig cells in the testis. Ablation of GPRC6A resulted in feminization of male GPRC6A−/− mice in association with decreased lean body mass, increased fat mass, increased circulating levels of estradiol, and reduced levels of testosterone. GPRC6A was also highly expressed in kidney proximal and distal tubules, and GPRC6A−/− mice exhibited increments in urine Ca/Cr and PO4/Cr ratios as well as low molecular weight proteinuria. Finally, GPRC6A−/− mice exhibited a decrease in bone mineral density (BMD) in association with impaired mineralization of bone.
Conclusions/Significance
GPRC6A−/− mice have a metabolic syndrome characterized by defective osteoblast-mediated bone mineralization, abnormal renal handling of calcium and phosphorus, fatty liver, glucose intolerance and disordered steroidogenesis. These findings suggest the overall function of GPRC6A may be to coordinate the anabolic responses of multiple tissues through the sensing of extracellular amino acids, osteocalcin and divalent cations.
doi:10.1371/journal.pone.0003858
PMCID: PMC2585477  PMID: 19050760
24.  Identification of a Novel Extracellular Cation-sensing G-protein-coupled Receptor* 
The Journal of biological chemistry  2005;280(48):40201-40209.
The C family G-protein-coupled receptors contain members that sense amino acid and extracellular cations, of which calcium-sensing receptor (CASR) is the prototypic extracellular calcium-sensing receptor. Some cells, such as osteoblasts in bone, retain responsiveness to extracellular calcium in CASR-deficient mice, consistent with the existence of another calcium-sensing receptor. We examined the calcium-sensing properties of GPRC6A, a newly identified member of this family. Alignment of GPRC6A with CASR revealed conservation of both calcium and calcimimetic binding sites. In addition, calcium, magnesium, strontium, aluminum, gadolinium, and the calcimimetic NPS 568 resulted in a dose-dependent stimulation of GPRC6A overexpressed in human embryonic kidney cells 293 cells. Also, osteocalcin, a calcium-binding protein highly expressed in bone, dose-dependently stimulated GPRC6A activity in the presence of calcium but inhibited the calcium-dependent activation of CASR. Coexpression of β-arrestins 1 and 2, regulators of G-protein signaling RGS2 or RGS4, the RhoA inhibitor C3 toxin, the dominant negative Gαq-(305–359) minigene, and pretreatment with pertussis toxin inhibited activation of GPRC6A by extracellular cations. Reverse transcription-PCR analyses showed that mouse GPRC6A is widely expressed in mouse tissues, including bone, calvaria, and the osteoblastic cell line MC3T3-E1. These data suggest that in addition to sensing amino acids, GPRC6A is a cation-, calcimimetic-, and osteocalcin-sensing receptor and a candidate for mediating extracellular calcium-sensing responses in osteoblasts and possibly other tissues.
doi:10.1074/jbc.M505186200
PMCID: PMC1435382  PMID: 16199532

Results 1-24 (24)