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1.  Pericyte Dynamics during Angiogenesis: New Insights from New Identities 
Journal of vascular research  2014;51(3):163-174.
Therapies aimed at manipulating the microcirculation require the ability to control angiogenesis, defined as the sprouting of new capillaries from existing vessels. In multiple pathologies (cancer, retinopathies, rheumatoid arthritis), blocking angiogenesis would be beneficial. In others (myocardial infarction, stroke, hypertension), promoting angiogenesis would be desirable. We know vascular pericytes elongate around endothelial cells and are functionally associated with regulating vessel stabilization, vessel diameter, and endothelial cell proliferation. During angiogenesis, bidirectional pericyte-endothelial cell signaling is critical for capillary sprout formation. Observations of pericytes leading capillary sprouts also implicate their role in endothelial cell guidance. As such, pericytes have recently emerged as a therapeutic target to promote or inhibit angiogenesis. Advancing our basic understanding of pericytes and the ability to develop pericyte-related therapies are challenged, like in many other fields, by questions regarding cell identity. This review article discusses what we know about pericyte phenotypes and the opportunity to advance our understanding of pericytes by defining specific pericyte cell populations involved in capillary sprouting.
doi:10.1159/000362276
PMCID: PMC4149862  PMID: 24853910
pericyte; angiogenesis; capillary; sprouting; phenotype
2.  Targeting Perciytes for Angiogenic Therapies 
In pathological scenarios, such as tumor growth and diabetic retinopathy, blocking angiogenesis would be beneficial. In others, such as myocardial infarction and hypertension, promoting angiogenesis might be desirable. Due to their putative influence on endothelial cells, vascular pericytes have become a topic of growing interest and are increasingly being evaluated as a potential target for angioregulatory therapies. For example, the strategy of manipulating pericyte recruitment to capillaries could result in anti- or pro-angiogenic effects. However, our current understanding of pericytes is limited by knowledge gaps regarding pericyte identity and lineage. To use a music analogy, this review is a “mash-up” that attempts to integrate what we know about pericyte functionality and expression with what is beginning to be elucidated regarding their regenerative potential. We explore the lingering questions regarding pericyte phenotypic identity and lineage. The expression of different pericyte markers (e.g., SMA, Desmin, NG2 and PDGFR-β) varies for different subpopulations and tissues. Previous use of these markers to identify pericytes has suggested potential phenotypic overlaps and plasticity toward other cell phenotypes. Our review chronicles the state of the literature, identifies critical unanswered questions, and motivates future research aimed at understanding this intriguing cell type and harnessing its therapeutic potential.
doi:10.1111/micc.12107
PMCID: PMC4079092  PMID: 24267154
pericytes; stem cell; angiogenesis; therapy
3.  Relationships Between Lymphangiogenesis and Angiogenesis During Inflammation in Rat Mesentery Microvascular Networks 
Lymphatic Research and Biology  2012;10(4):198-207.
Abstract
Background
Lymphatic and blood microvascular systems play a coordinated role in the regulation of interstitial fluid balance and immune cell trafficking during inflammation. The objective of this study was to characterize the temporal and spatial relationships between lymphatic and blood vessel growth in the adult rat mesentery following an inflammatory stimulus.
Methods and Results
Mesenteric tissues were harvested from unstimulated adult male Wistar rats and at 3, 10, and 30 days post compound 48/80 stimulation. Tissues were immunolabeled for PECAM, LYVE-1, Prox1, podoplanin, CD11b, and class III β-tubulin. Vascular area, capillary blind end density, and vascular length density were quantified for each vessel system per time point. Blood vascular area increased compared to unstimulated tissues by day 10 and remained increased at day 30. Following the peak in blood capillary sprouting at day 3, blood vascular area and density increased at day 10. The number of blind-ended lymphatic vessels and lymphatic density did not significantly increase until day 10, and lymphatic vascular area was not increased compared to the unstimulated level until day 30. Lymphangiogenesis correlated with the upregulation of class III β-tubulin expression by endothelial cells along lymphatic blind-ended vessels and increased lymphatic/blood endothelial cell connections. In local tissue regions containing both blood and lymphatic vessels, the presence of lymphatics attenuated blood capillary sprouting.
Conclusions
Our work suggests that lymphangiogenesis lags angiogenesis during inflammation and motivates the need for future investigations aimed at understanding lymphatic/blood endothelial cell interactions. The results also indicate that lymphatic endothelial cells undergo phenotypic changes during lymphangiogenesis.
doi:10.1089/lrb.2012.0014
PMCID: PMC3525890  PMID: 23240958
4.  Cell proliferation along vascular islands during microvascular network growth 
BMC Physiology  2012;12:7.
Background
Observations in our laboratory provide evidence of vascular islands, defined as disconnected endothelial cell segments, in the adult microcirculation. The objective of this study was to determine if vascular islands are involved in angiogenesis during microvascular network growth.
Results
Mesenteric tissues, which allow visualization of entire microvascular networks at a single cell level, were harvested from unstimulated adult male Wistar rats and Wistar rats 3 and 10 days post angiogenesis stimulation by mast cell degranulation with compound 48/80. Tissues were immunolabeled for PECAM and BRDU. Identification of vessel lumens via injection of FITC-dextran confirmed that endothelial cell segments were disconnected from nearby patent networks. Stimulated networks displayed increases in vascular area, length density, and capillary sprouting. On day 3, the percentage of islands with at least one BRDU-positive cell increased compared to the unstimulated level and was equal to the percentage of capillary sprouts with at least one BRDU-positive cell. At day 10, the number of vascular islands per vascular area dramatically decreased compared to unstimulated and day 3 levels.
Conclusions
These results show that vascular islands have the ability to proliferate and suggest that they are able to incorporate into the microcirculation during the initial stages of microvascular network growth.
doi:10.1186/1472-6793-12-7
PMCID: PMC3493275  PMID: 22720777
Angiogenesis; Microcirculation; Mesentery; Proliferation; Endothelial cell
5.  Rat Mesentery Exteriorization: A Model for Investigating the Cellular Dynamics Involved in Angiogenesis 
Microvacular network growth and remodeling are critical aspects of wound healing, inflammation, diabetic retinopathy, tumor growth and other disease conditions1, 2. Network growth is commonly attributed to angiogenesis, defined as the growth of new vessels from pre-existing vessels. The angiogenic process is also directly linked to arteriogenesis, defined as the capillary acquisition of a perivascular cell coating and vessel enlargement. Needless to say, angiogenesis is complex and involves multiple players at the cellular and molecular level3. Understanding how a microvascular network grows requires identifying the spatial and temporal dynamics along the hierarchy of a network over the time course of angiogenesis. This information is critical for the development of therapies aimed at manipulating vessel growth.
The exteriorization model described in this article represents a simple, reproducible model for stimulating angiogenesis in the rat mesentery. It was adapted from wound-healing models in the rat mesentery4-7, and is an alternative to stimulate angiogenesis in the mesentery via i.p. injections of pro-angiogenic agents8, 9. The exteriorization model is attractive because it requires minimal surgical intervention and produces dramatic, reproducible increases in capillary sprouts, vascular area and vascular density over a relatively short time course in a tissue that allows for the two-dimensional visualization of entire microvascular networks down to single cell level. The stimulated growth reflects natural angiogenic responses in a physiological environment without interference of foreign angiogenic molecules. Using immunohistochemical labeling methods, this model has been proven extremely useful in identifying novel cellular events involved in angiogenesis. Investigators can readily correlate the angiogenic metrics during the time course of remodeling with time specific dynamics, such as cellular phenotypic changes or cellular interactions4, 5, 7, 10, 11.
doi:10.3791/3954
PMCID: PMC3466932  PMID: 22643964
Cellular Biology;  Issue 63;  mesentery;  rat;  angiogenesis;  microcirculation;  microvascular;  remodeling
6.  Human Adipose-Derived Stromal Cells Accelerate Diabetic Wound Healing: Impact of Cell Formulation and Delivery 
Tissue Engineering. Part A  2010;16(5):1595-1606.
Human adipose-derived stromal cells (ASCs) have been shown to possess therapeutic potential in a variety of settings, including cutaneous wound healing; however, it is unknown whether the regenerative properties of this cell type can be applied to diabetic ulcers. ASCs collected from elective surgical procedures were used to treat full-thickness dermal wounds in leptin receptor-deficient (db/db) mice. Cells were delivered either as multicellular aggregates or as cell suspensions to determine the impact of cell formulation and delivery methods on biological activity and in vivo therapeutic effect. After treatment with ASCs that were formulated as multicellular aggregates, diabetic wounds experienced a significant increase in the rate of wound closure compared to wounds treated with an equal number of ASCs delivered in suspension. Analysis of culture supernatant and gene arrays indicated that ASCs formulated as three-dimensional aggregates produce significantly more extracellular matrix proteins (e.g., tenascin C, collagen VI α3, and fibronectin) and secreted soluble factors (e.g., hepatocyte growth factor, matrix metalloproteinase-2, and matrix metalloproteinase-14) compared to monolayer culture. From these results, it is clear that cell culture, formulation, and delivery method have a large impact on the in vitro and in vivo biology of ASCs.
doi:10.1089/ten.tea.2009.0616
PMCID: PMC2952117  PMID: 20038211

Results 1-6 (6)