Soluble receptor variants fine-tune placental blood vessel growth, study finds

The placenta is one of the most remarkable engineering feats of human biology, building an intricate network of fetal blood vessels in a matter of weeks to deliver oxygen and nutrients to a growing baby. When that construction goes wrong, the consequences can be devastating, ranging from fetal growth restriction and preterm birth to lifelong cardiovascular and neurodevelopmental complications. A new study published in the journal Angiogenesis now adds a surprising new character to the molecular drama that governs this process: soluble fragments of the platelet-derived growth factor receptor beta, known as sPDGFRβ, which appear to act as built-in braking systems for one of the most important signaling pathways in vascular development.

The research, led by Audra R. Barnes-Lanier and John C. Chappell at Virginia Tech’s Fralin Biomedical Research Institute, provides the first detailed look at how these soluble receptor variants behave in the developing placenta of both mice and humans. The team documented progressively increasing pericyte coverage of fetoplacental capillaries across gestation, confirmed that placental pericytes display the same phenotypic diversity seen in the brain, heart, and lungs, and then demonstrated that soluble PDGFRβ isoforms are produced at both the RNA and protein levels throughout pregnancy. Most intriguingly, their functional experiments suggest these soluble fragments can modulate the very signaling pathway that recruits pericytes to nascent blood vessels in the first place.

Pericytes are specialized mural cells that wrap around capillaries, reinforcing vessel integrity and coordinating vascular maturation through intimate communication with endothelial cells. The primary chemical conversation between these two cell types runs through platelet-derived growth factor-BB, or PDGF-BB, which endothelial cells display on their surfaces to attract PDGFRβ-bearing pericytes. Decades of genetic work have shown that this pathway must be calibrated with extraordinary precision. Too little PDGF-BB signaling and pericytes abandon the vessel wall, leaving fragile, leaky, hemorrhage-prone capillaries; in mice, loss of PDGF-B or PDGFRβ produces placental abnormalities among a constellation of developmental defects. Too much signaling, on the other hand, drives pericyte hyperproliferation, vascular malformations, and fibrosis, as seen in patients carrying activating PDGFRB mutations.

Soluble receptor isoforms have emerged as one way biology walks this tightrope. Across the receptor tyrosine kinase family, truncated receptor variants generated by alternative mRNA splicing or proteolytic cleavage can act as decoys, sponging up ligand or interfering with full-length receptor activity. The most celebrated example is soluble Flt-1, or sFlt-1, which restrains VEGF-A signaling during vascular sprouting and, when misregulated in the placenta, becomes a central driver of preeclampsia. Until recently, however, soluble PDGFRβ was largely viewed as a degradation product, a biomarker of pericyte damage detected in the aging and diseased brain rather than a molecule with a job of its own. That view began to shift when the Chappell laboratory and collaborators showed that alternatively spliced sPDGFRβ transcripts and proteins are produced under entirely normal developmental conditions.

In the new work, the team turned to the placenta to ask whether these variants might matter during pregnancy. Examining mouse placentas at embryonic days 9.5, 14.5, and 18.5, they found that NG2-positive pericytes appear alongside the earliest vasculogenic structures and progressively invest the expanding capillary network, matching the pace of endothelial growth. Transcriptional analysis confirmed rising expression of pericyte genes including Cspg4, Acta2, and full-length Pdgfrβ across gestation, alongside coordinated changes in the Vegfa, Flt-1, and Pdgfb pathways. Western blotting revealed parallel increases in both the full-length receptor, at roughly 160 kilodaltons, and truncated soluble isoforms. Human placenta samples from uncomplicated full-term pregnancies told the same story, with full-length PDGFRβ and a shorter, soluble variant present in every quadrant examined, though with notable regional heterogeneity across the organ.

To dissect how sPDGFRβ is regulated and what it does, the researchers exploited a murine trophoblast and embryonic stem cell differentiation model, or TESC model, that recapitulates key features of early placental vascular development. As these stem cells differentiated, they formed primitive vascular networks containing fluorescently labeled endothelial cells and pericyte progenitors, while also generating trophoblast lineage cells marked by cytokeratins and the tight junction protein ZO-1, mirroring the cellular constituents of the developing placenta. Within this system, soluble PDGFRβ proteins appeared and accumulated alongside full-length receptor during vessel formation, accompanied by transcripts encoding intron-4 and intron-10 truncation variants previously characterized in the healthy brain.

The regulation experiments yielded two unexpected findings. First, blocking the metalloprotease ADAM10, long implicated in shedding soluble PDGFRβ from damaged pericytes, had no effect on soluble receptor levels during early vessel formation, and instead increased full-length receptor abundance, suggesting that in the developmental context, alternative mRNA splicing rather than proteolytic cleavage is the dominant source. Second, exogenous growth factors failed to boost sPDGFRβ production; adding VEGF-A or PDGF-BB to the cultures actually lowered soluble isoform levels slightly, while PDGF-BB significantly reduced full-length receptor, consistent with ligand-induced receptor internalization and degradation. Hypoxia, however, proved to be a powerful stimulus, driving a robust and sustained increase in soluble PDGFRβ protein after just 12 hours at 3 percent oxygen, and again at 48 hours, while full-length receptor remained unchanged.

That hypoxic sensitivity may be the key to the whole story, because low oxygen tension is a defining feature of early placentation and a hallmark of placental insufficiency. To test whether elevated sPDGFRβ could actually influence PDGF-BB signaling, the team added a soluble receptor mimetic, a peptide spanning the PDGF-BB ligand-binding domain, to their developing vascular networks. As expected, excess PDGF-BB alone reduced full-length PDGFRβ levels while increasing phosphorylation of the receptor at a key regulatory tyrosine residue. But when the mimetic was co-administered, both effects were attenuated, pulling receptor abundance and phosphorylation back toward baseline. The result supports a model in which soluble PDGFRβ acts as a negative feedback modulator, buffering PDGF-BB signaling against overshoot, particularly when hypoxia threatens to destabilize the system.

The implications reach well beyond basic vascular biology. Pericyte dysfunction at the maternal-fetal interface is increasingly implicated in preeclampsia, fetal growth restriction, and the abnormal, poorly perfused vessels that characterize placental insufficiency, conditions that also elevate sFlt-1 and disrupt maternal cardiovascular health. If sPDGFRβ proves to be similarly misregulated in pathological pregnancies, it could serve as both a biomarker for stratifying at-risk patients and a therapeutic target for stabilizing fetoplacental vascular maturation. The authors also point to broader questions about why pericytes diversify into contractile and non-contractile subtypes across organs, and how RNA-binding proteins and splicing factors orchestrate soluble receptor production. Follow-on studies are already planned to validate sPDGFRβ transcript and protein structures, screen disease databases for associations with placental dysfunction, and determine whether the same oxygen-sensitive feedback loop protects, or fails to protect, the fragile vasculature of pregnancies under stress.

The placenta offers an unusually instructive setting in which to study soluble receptor biology because its oxygen environment changes dramatically over the course of gestation. Early placentation occurs under relatively low oxygen tension, a physiological state that protects the developing embryo from oxidative damage while the fetoplacental circulation is still being assembled. The observation that hypoxia robustly increased soluble PDGFRβ production in the TESC model, without altering full-length receptor abundance, suggests that the placenta may naturally encounter conditions that favor soluble isoform generation precisely when vascular remodeling is most active. This oxygen-sensitive behavior distinguishes sPDGFRβ from many other signaling modulators whose expression is driven primarily by ligand availability.

The distinction between alternatively spliced and proteolytically shed soluble receptor variants carries practical consequences for future research. Shed receptor fragments released from damaged pericytes have historically been interpreted as passive markers of injury, whereas splice-derived isoforms represent deliberate gene products that can be regulated independently of cell death or membrane cleavage. The finding that ADAM10 inhibition did not reduce soluble receptor levels during early vessel formation, and instead raised full-length receptor abundance, implies that the developmental placenta relies on transcriptional mechanisms rather than ectodomain shedding. This matters therapeutically, because strategies targeting metalloprotease activity would be unlikely to influence a splicing-derived soluble pool, while interventions aimed at splicing factors or RNA-binding proteins might.

The TESC differentiation model itself deserves attention as a methodological advance. Placental tissue is difficult to obtain and study experimentally, particularly at early developmental stages, and animal models do not fully capture human trophoblast biology. A system in which trophoblast lineage cells, endothelial cells, and pericyte progenitors arise together and assemble vascular-like networks provides a tractable platform for testing how individual signaling components behave in a placental context. The demonstration that soluble PDGFRβ isoforms appear in this model at both transcript and protein levels, matching what is seen in native mouse and human tissue, strengthens confidence that the model reflects genuine developmental regulation rather than an artifact of cell culture.

Several questions remain open before these findings can be translated. The functional experiments relied on a mimetic peptide spanning the ligand-binding domain, so it is not yet certain that endogenously produced soluble isoforms exert identical effects in vivo. The precise stoichiometry between soluble receptor, PDGF-BB ligand, and membrane-bound PDGFRβ that produces meaningful modulation of signaling has not been defined. Whether soluble PDGFRβ sequesters ligand directly, competes for receptor binding, or acts through some other mechanism also remains to be resolved. Answering these questions will require genetic models in which soluble isoform production can be selectively manipulated, allowing investigators to separate the contributions of splicing-derived variants from the full-length receptor they appear to regulate.

Subject of Research: Regulation of PDGF-BB signaling in placental pericytes by soluble PDGFRβ isoforms during fetoplacental vascular development

Article Title: Regulation of PDGF-BB signaling in placental pericytes by soluble PDGFRβ isoforms: implications for fetoplacental vascular development

Article References: Barnes-Lanier, A. R., Duggan, E. C., Dunkenberger, R. A., Lessard, C. V., Cosma, C. C., Steele, C. R., Taylor, S. V., Darden, J. A., Whitham, M. D., Durica, A. R., & Chappell, J. C. (2026). Regulation of PDGF-BB signaling in placental pericytes by soluble PDGFRβ isoforms: implications for fetoplacental vascular development. Angiogenesis, 29(4), Article 67. https://doi.org/10.1007/s10456-026-10091-3

Image Credits: AI Generated

DOI: 10.1007/s10456-026-10091-3

Keywords: placenta, pericytes, PDGF-BB, PDGFRβ, soluble receptor, angiogenesis, fetal development, hypoxia, endothelial cells, preeclampsia, vascular development, alternative splicing