In regenerative medicine, the ability to engineer functional, long-lasting vascular networks is a defining challenge. Without a stable blood supply, engineered tissues fail to survive beyond a few hundred microns, succumbing to hypoxia and nutrient deprivation. While endothelial cells have long been the focus of vascular tissue engineering, a growing body of evidence underscores the critical role of pericytes—mural cells that wrap around capillaries and microvessels—in stabilizing, maturing, and regulating these nascent networks. Understanding pericyte biology and learning to harness their stabilizing effects is key to moving tissue-engineered constructs from the lab bench to clinical reality. This article explores the multifaceted role of pericytes in vascular stabilization, their mechanisms of action, and how these insights are being applied to engineer robust vascular networks for regenerative therapies.

What Are Pericytes?

Pericytes are contractile, mesenchymal-like cells that reside on the abluminal surface of capillaries and post-capillary venules. They are embedded within the basement membrane and extend long processes that wrap around endothelial cells, with which they form direct contact via peg-and-socket junctions. Pericytes are not a uniform population; they exhibit remarkable heterogeneity in morphology, origin, and marker expression depending on the tissue bed. Commonly used markers include platelet-derived growth factor receptor beta (PDGFRβ), neural/glial antigen 2, α-smooth muscle actin (αSMA), desmin, and regulator of G-protein signaling 5 (RGS5). Their origin can be traced to mesoderm-derived progenitors such as neural crest cells in the head and mesothelial cells in other tissues, and even to bone marrow–derived precursors under certain conditions.

Pericyte coverage varies widely across organs—from approximately 1:3 in skeletal muscle to 1:1 in the central nervous system, where they are critical for blood-brain barrier integrity. This anatomic positioning places pericytes at the hub of blood vessel development, maintenance, and remodeling. For a comprehensive review of pericyte developmental biology, see Armulik et al., 2011.

The Role of Pericytes in Vascular Stability

During angiogenesis, endothelial cells first form a primitive tubular network that is inherently leaky and unstable. Pericytes are recruited to these nascent vessels and, through reciprocal signaling, promote vessel maturation, quiescence, and stability. Their presence reduces endothelial proliferation, tightens endothelial junctions, and deposits extracellular matrix components that reinforce the vascular wall. In engineered systems, the absence of pericytes typically results in rapid vessel regression or aberrant remodeling when transplanted into a host environment.

Pericyte-Endothelial Cell Signaling

The dialogue between pericytes and endothelial cells is mediated by several well-characterized signaling pathways that collectively orchestrate pericyte recruitment, differentiation, and attachement.

PDGF-B/PDGFR-β Pathway

Endothelial cells secrete platelet-derived growth factor B (PDGF-B), which binds to PDGFR-β on pericytes, acting as a mitogen and chemoattractant. This signaling is essential for pericyte recruitment during development and in adult angiogenesis. Disruption of PDGF-B or PDGFR-β leads to pericyte deficiency, microvascular hemorrhage, and embryonic lethality. In tissue engineering, exogenous PDGF-B delivery or co-expression in endothelial cells can enhance pericyte coverage and network stability.

TGF-β Signaling

Transforming growth factor beta (TGF-β) plays a dual role in angiogenesis. At early stages, it inhibits endothelial proliferation; later, it stimulates pericyte differentiation and extracellular matrix deposition. TGF-β signaling via ALK5 and Smad pathways in pericytes promotes αSMA expression and contractility, thereby stabilizing newly formed vessels. Blocking TGF-β signaling in co-culture models results in immature, poorly stabilized networks.

Angiopoietin-Tie2 Axis

Angiopoietin-1 (Ang-1) secreted by pericytes binds to Tie2 receptors on endothelial cells, promoting vessel stabilization, reducing permeability, and inhibiting endothelial apoptosis. Conversely, Ang-2 (often released by endothelial cells under stress) acts as a context-dependent antagonist, destabilizing vessels and allowing vascular regression or remodeling. Engineering Ang-1 overexpression or using Ang-2 blocking strategies has been explored to improve pericyte-mediated stabilization in engineered constructs.

Notch and Ephrin Pathways

Notch signaling between pericytes and endothelial cells regulates arteriovenous specification and pericyte coverage. EphrinB2 reverse signaling in pericytes is also required for proper mural cell investment. These pathways add another layer of complexity and opportunity for targeted engineering.

Extracellular Matrix Remodeling

Pericytes are active producers of basement membrane components including collagen type IV, laminin, nidogen, and perlecan. They also secrete matrix metalloproteinases (MMPs) and their inhibitors (TIMPs), enabling controlled matrix turnover that is essential for vessel sprouting and stabilization. In engineered vascular networks, co-culturing pericytes with endothelial cells in a pro-matrix environment (e.g., fibrin or collagen gels) leads to more robust basement membrane deposition and reduced vessel leakiness.

Contractile Function and Blood Flow Regulation

Unlike smooth muscle cells that regulate larger vessels, pericytes can contract and relax to modulate capillary diameter, thereby controlling local blood flow. This contractility is calcium-dependent and mediated by αSMA and non-muscle myosin. In the brain, pericyte contraction is implicated in neurovascular coupling. In engineered tissues, incorporating pericytes can provide a mechanism for dynamic flow regulation, though achieving physiological contractility in vitro requires appropriate substrate stiffness and signaling cues.

Pericytes in Engineered Tissues

Recognizing the stabilizing influence of pericytes, tissue engineers have developed strategies to incorporate them into vascularized constructs. These approaches aim to mimic the native perivascular niche and produce durable, functional microvessels that can anastomose with host circulation.

In Vitro Co-Culture Models

The most straightforward strategy is to co-culture endothelial cells with pericyte progenitors (such as mesenchymal stem cells or adipose-derived stem cells) in a 3D scaffold or hydrogel. Numerous studies have shown that such co-cultures produce denser, more stable, and longer-lasting capillary-like networks compared to endothelial cells alone. For instance, Geevarghese & Herman (2014) demonstrate that human brain pericytes cocultured with endothelial cells in collagen gels significantly increase vessel diameter and basement membrane deposition.

Advances in microfluidic technologies now allow for precisely controlled coculture systems where pericyte recruitment can be visualized in real time. These devices also enable application of fluid shear stress, which further stabilizes the networks and promotes pericyte alignment.

Integration with Host Vasculature

For clinical translation, engineered vessels must anastomose with the host's own circulation. In animal models, constructs containing both endothelial cells and pericytes show dramatically improved perfusion and patency after implantation. Pericytes not only prevent vessel regression but also promote host vessel ingrowth via paracrine secretion of angiogenic factors such as VEGF and PDGF-BB. Recent work using iPSC-derived pericytes demonstrates that these cells can survive long-term and maintain a perivascular position in vivo, providing a renewable cell source for engineered tissues.

Challenges in Engineering Pericyte-Lined Vessels

Despite these promising results, challenges remain. Pericytes can become activated and transition into myofibroblasts, contributing to fibrosis or stenosis if not properly regulated. Identifying the right pericyte subtype, optimizing culture conditions, and controlling matrix stiffness are critical. Additionally, purification of pericyte populations away from other stromal cells is necessary to avoid undesirable heterogeneity. Scalable manufacturing and regulatory hurdles also need to be addressed before pericyte-based vascular engineering can enter clinical trials.

Implications for Regenerative Medicine

The ability to stabilize engineered blood vessels with pericytes has profound implications across multiple therapeutic areas.

Wound Healing and Skin Regeneration

Chronic wounds often suffer from poor vascularization. Applying pericyte-laden dermal substitutes or directly delivering pericyte-derived factors can promote angiogenesis and accelerate closure. Preclinical studies using pericyte-seeded scaffolds in diabetic wound models show enhanced granulation tissue formation and faster re-epithelialization compared to acellular controls.

Cardiac and Skeletal Muscle Repair

After myocardial infarction or volumetric muscle loss, revascularization is essential for survival of grafts and regeneration of functional tissue. Pericytes, especially those derived from the same tissue, are being explored as a cell therapy. They not only stabilize blood vessels but also exert immunomodulatory and pro-regenerative effects. For example, cardiac pericytes can enhance angiogenesis and reduce fibrosis after ischemia-reperfusion injury.

Organoids and Vascularized Tissues

Organoid technology relies on self-organization of multiple cell types, but many organoids lack functional vasculature and therefore suffer from a necrotic core. Incorporating pericytes alongside endothelial cells within organoid culture systems is a promising strategy to create more complex, vascularized mini-organs that better recapitulate native tissue architecture.

Idiopathic Pulmonary Fibrosis and Other Diseases

While not directly a regenerative application, understanding pericyte function is crucial for disease modeling. Pericytes are implicated in fibrotic diseases where they transition to fibroblasts and contribute to matrix deposition. Engineering pericyte-stabilized microvessels in a dish can serve as a platform to study these transitions and screen for anti-fibrotic compounds.

Future Directions and Clinical Translation

The next decade will likely see pericyte-focused vascular engineering move from proof-of-concept to more sophisticated clinical products. Emerging technologies such as 3D bioprinting allow precise placement of pericytes along endothelial-lined channels, creating hierarchical vascular trees. Gene editing tools (CRISPR) can be used to modulate pericyte behavior—for instance, knocking out pro-fibrotic genes or expressing stabilizing factors like Ang-1 under a pericyte-specific promoter.

Another frontier is the use of pericyte-derived extracellular vesicles (EVs) as a cell-free therapy. These EVs carry miRNA and proteins that can stabilize vessels without the risks associated with live cell transplantation. Preliminary data suggest pericyte EVs reduce vascular permeability and promote angiogenesis in ischemic models, offering a scalable off-the-shelf alternative.

Finally, regulatory frameworks need to adapt to the complexity of multi-cellular engineered products. Clinical trials for vascularized tissues, such as the U.S. FDA’s guidance on combined devices and cellular therapies, will require robust characterization of pericyte identity, purity, and function. Despite these hurdles, the foundational biology is sound: pericytes are indispensable for stable, functional blood vessels, and engineering them into our constructs is a logical and necessary step toward realizing the promise of regenerative medicine.

In summary, pericytes are not merely support cells but active regulators of vascular stability. By integrating pericyte biology into tissue engineering strategies—through co-culture, signaling pathway modulation, and advanced fabrication methods—we can create vascular networks that survive, function, and integrate. This pericyte-centric approach will accelerate the translation of many regenerative therapies, from skin grafts to whole organ replacements.