The research team, led by investigators at the University of Edinburgh and the UK Dementia Research Institute, analysed post-mortem brain tissue from 20 cases spanning the full spectrum of cerebral small vessel disease severity, from healthy controls to severe disease. The tissue, drawn from the Lothian Birth Cohort, the LINCHPIN study, and the Edinburgh Sudden Death Brain Bank, came from Brodmann area 4, the primary motor cortex, an understudied region in this disease. Using multiplex immunohistochemistry combined with spectral unmixing and automated image analysis, the researchers dissected 11,409 individual microvascular fragments, tracking three molecular markers simultaneously: PECAM-1 to identify endothelial cells, PDGFRβ to label pericytes, and VCAM-1 as a readout of endothelial activation.

The technical achievement underlying the study is considerable. Aged human brain tissue is notorious for autofluorescence, particularly from lipofuscin pigment, which confounds conventional immunofluorescence. The team sidestepped this problem with chromogenic multiplex staining imaged across 20 wavelengths on a liquid–crystal tuneable band-pass filter system, then computationally unmixed the overlapping chromogen signals into separate pseudo-fluorescent channels. A MATLAB-based segmentation pipeline called Morph-O-Matic then extracted each vessel’s length, diameter, area, and marker signal intensities, with extreme values filtered out to remove segmentation artefacts. The result was a quantitative atlas of capillaries averaging 9.1 micrometres in diameter, the most abundant vascular bed in brain tissue.

The first surprise came from vascular architecture. In healthy controls, white matter vessels were 51 percent less dense and 14 percent wider than their grey matter counterparts, underscoring the inherent vulnerability of white matter. As disease severity increased, vessel diameter remained essentially stable — but microvascular density in white matter doubled in severe cases compared with controls, and correlated strongly with age at death. This finding runs counter to previous reports of age-related capillary rarefaction. The authors suggest the increase may represent compensatory remodelling in response to hypoxia or hypoperfusion in deeper brain regions, noting that their sampling focused on superficial cortical layers and adjacent white matter, where cSVD-related remodelling is typically less pronounced.

The molecular story was more dramatic. PDGFRβ signal, a proxy for pericyte coverage, plummeted with increasing disease severity — dropping 94 percent in grey matter and 87 percent in white matter in the most severely affected cases relative to controls. The decline correlated robustly with both disease severity and age, and white matter pericyte signal was already 52 percent lower than grey matter even in healthy brains. In parallel, the endothelial markers climbed: PECAM-1 rose by 41 to 67 percent and VCAM-1 more than doubled in severe disease, hallmarks of a shift toward a pro-inflammatory, pro-thrombotic endothelial phenotype that promotes leukocyte adhesion and blood–brain barrier disruption.

But here lies the study’s central twist: when the researchers looked for a direct relationship between pericyte loss and endothelial activation, they found none. There was no clear correlation between falling PDGFRβ and rising VCAM-1 or PECAM-1. Instead, the data displayed striking heterogeneity, particularly in the intermediate severity groups, where some vessels retained robust pericyte coverage while others showed marked depletion. This heterogeneity, invisible to the bulk and region-averaged analyses that have dominated earlier neuropathological studies, may help explain why the literature has long been split between reports of pericyte loss and reports of preserved pericyte coverage in dementia.

To bring order to this complexity, the team applied unsupervised Gaussian mixture clustering to the three marker signals. The analysis resolved three distinct vascular states. Cluster 1 combined high pericyte coverage with low endothelial activation and contained all the healthy controls, plus a few mild and moderate cases. Cluster 2 showed reduced pericyte signal without endothelial activation, grouping intermediate cases. Cluster 3 paired pericyte loss with the highest levels of endothelial activation and captured all severe cases plus one moderate case. Notably, the marker-based clusters separated the cases more cleanly than the neuropathological diagnosis alone, as judged by PERMANOVA statistics, yet the authors are careful to stress that the clusters are descriptive molecular phenotypes, not proven sequential stages of disease.

Complementing the post-mortem work, the researchers examined circulating PDGF-BB and VCAM-1 in a previously published cohort of lacunar stroke patients. Patients whose blood showed high VCAM-1 with low PDGF-BB were significantly older than those in other biomarker quadrants, and their white matter damage scores, while highest, were no longer significant after adjusting for age. These exploratory data provide clinical context linking vascular marker profiles to ageing, but the authors emphasise they do not establish any temporal relationship between pericyte and endothelial changes.

The study also caught microglia in the act of change. In severe disease, Iba1-positive microglial profiles appeared more amoeboid, with segmented particle counts 46 percent lower and median particle areas up to 60 percent larger in grey matter compared with milder cases — a pattern consistent with reduced ramification and microglial activation. This supports the idea that advanced small vessel disease engages the wider neurogliovascular unit, though the thin 4-micrometre sections used precluded detailed reconstruction of microglial morphology or direct assessment of microglia–vessel interactions.

The authors are candid about the limitations. The cohort of 20 cases is small, the controls were not age-matched — a confound that partially entangles disease with ageing — and only five participants were female. Two severe cases also carried mild cerebral amyloid angiopathy, a potential confounder that could not be assessed separately. The anatomical scope was restricted to one cortical region and superficial white matter, whereas small vessel disease pathology is often most pronounced in deep white matter. And because the measurements are post-mortem marker expression, they do not directly measure blood–brain barrier permeability, tight junction integrity, or vascular physiology. Larger, longitudinal studies incorporating leakage markers and functional systems will be needed to determine whether the three vascular states are mechanistically connected or occur in a defined sequence.

Even with those caveats, the framework emerging from this work is a significant step forward. By showing that pericyte alterations and endothelial activation are partially dissociated processes in human disease, the study challenges the simple narrative in which pericyte loss automatically triggers endothelial inflammation. Instead, the brain’s smallest vessels appear to occupy distinct molecular states — intact and quiescent, pericyte-depleted but calm, or pericyte-depleted and inflamed — that may respond differently to the disease-modifying therapies that cerebral small vessel disease so urgently awaits. For a condition with no approved treatments that alter its course, defining these microvascular phenotypes is the essential first step toward targeting them.

Subject of Research: Pericyte loss and endothelial activation states in the human cerebral microvasculature in small vessel disease

Article Title: Pericyte loss and endothelial activation define distinct vascular states in cerebral small vessel disease

Article References: Chagnot, A., Jaime Garcia, D., McQuaid, C., Cholewa-Waclaw, J., McDade, K., Dando, O., Wardlaw, J. M., Smith, C., & Montagne, A. (2026). Pericyte loss and endothelial activation define distinct vascular states in cerebral small vessel disease. Acta Neuropathologica, 152(1), Article 53. https://doi.org/10.1007/s00401-026-03102-6

Image Credits: AI Generated

DOI: 10.1007/s00401-026-03102-6

Keywords: cerebral small vessel disease, pericytes, endothelial activation, blood–brain barrier, PDGFRβ, VCAM-1, PECAM-1, microvasculature, white matter, dementia, multiplex immunohistochemistry, ageing

The tracer at the center of the study, known as [68Ga]Ga-ATH001, is an Affibody molecule, a small engineered protein scaffold roughly a tenth the size of an antibody, that binds with picomolar affinity to platelet-derived growth factor receptor beta, or PDGFRβ. This receptor is a well-established hallmark of activated pericytes and, critically, of activated hepatic stellate cells, the liver-resident cells that transform into collagen-producing factories during fibrogenesis. Because PDGFRβ is upregulated on the cells actively driving extracellular matrix deposition across the liver, lung, heart and tumor stroma, it offers a molecular handle for imaging not the aftermath of scarring but the scarring process itself, while it is still underway and still treatable.

Before any new radiotracer can be used diagnostically, regulators and clinicians need to know exactly where it goes in the body and how much radiation it deposits along the way. That is the question the research team, led by Mark Lubberink of Uppsala University together with colleagues from Karolinska Institutet, Antaros Medical, Antaros Tracer and Takeda Development Center Americas, set out to answer in a first-in-human study registered as NCT06562361. The dosimetry cohort comprised six participants: three healthy volunteers, all 22 years old, and three patients with metabolic dysfunction-associated steatohepatitis, or MASH, the aggressive form of fatty liver disease in which fibrosis is a central driver of disease progression and mortality.

Each participant received an intravenous bolus of approximately 2.5 megabecquerels per kilogram of body weight of the gallium-68-labeled tracer, corresponding to an average injected activity of 178 MBq and a peptide mass of just 51 micrograms, roughly a thousandth of a drop of protein. Imaging began immediately, with a dynamic PET/MRI scan over the abdomen capturing the first 35 minutes of tracer distribution in real time, followed by whole-body PET scans at one, two and three hours after injection. In total, 25 organs and tissues were segmented and analyzed, from the liver, kidneys and spleen to the red bone marrow, salivary glands, thyroid and gonads, providing an unusually comprehensive map of the tracer’s journey through the body.

The biodistribution results told a clean and encouraging story. The tracer spread rapidly through the circulation and then cleared quickly from most tissues, so that by two hours after injection, radioactivity remained essentially only in the kidneys and bladder, the sole route of excretion, and in the spleen, which naturally expresses abundant PDGFRβ. In the healthy volunteers, liver uptake had already fallen close to background levels. In the MASH patients, by contrast, liver uptake was significantly higher, with a standardized uptake value of 4.0 compared with 2.8 in the healthy group, a difference the authors attribute to the upregulation of PDGFRβ on activated hepatic stellate cells engaged in ongoing fibrogenesis. In other words, the tracer did exactly what it was designed to do: distinguish fibrotically active livers from quiescent ones.

On the radiation side, the calculations, performed with the IDAC DOSE 2.1 software using the ICRP 103 framework and ICRP 110 reference phantoms scaled to each participant’s body weight, yielded a sex-averaged effective dose of 0.028 ± 0.002 millisieverts per megabecquerel. The kidneys emerged as the dose-limiting organ, absorbing 0.34 mGy/MBq in males and 0.46 mGy/MBq in females, a consequence of the renal tubules reabsorbing the peptide-based tracer and trapping the gallium-68 intracellularly, a well-known behavior of this class of small radiolabeled proteins. At the clinically targeted activity of 2 MBq per kilogram, roughly 150 MBq for a typical adult male, the total effective dose would come to 4.1 mSv, with kidney absorbed doses of about 50 mGy in males and 55 mGy in females.

Those numbers place [68Ga]Ga-ATH001 in familiar company. Its effective dose is comparable to other gallium-68-labeled Affibody molecules previously evaluated in humans and only slightly higher than that of established peptide tracers such as [68Ga]Ga-DOTATOC, used routinely in neuroendocrine tumor imaging, or the workhorse PET radiopharmaceutical fluorodeoxyglucose. Given that a single abdominal CT scan can deliver an effective dose in the range of 10 mSv, a 4.1 mSv PET study that can be repeated over months or years represents a radiation profile compatible with the longitudinal study designs that fibrosis research desperately needs, subject of course to applicable regulatory and ethical requirements.

Safety was equally reassuring. Participants were monitored for up to 24 hours after dosing with laboratory assessments, vital signs and electrocardiography, and none experienced any adverse effects following administration of up to 70 micrograms of the precursor peptide, approximately 0.9 micrograms per kilogram. The authors also carefully catalogued the uncertainties in their dosimetry, noting that the scan protocol, with its 35-minute dynamic acquisition followed by serial whole-body imaging, kept the extrapolated fraction of the time-integrated activity below 20 percent for most organs in the dynamic field of view, and that the bladder dose estimate, based solely on PET data without assuming voiding, likely overestimates the true absorbed dose.

The significance of this work extends well beyond liver disease. Because PDGFRβ activity is entwined with angiogenesis, tissue remodeling and wound healing throughout the body, a validated PET marker of the receptor opens the door to non-invasive monitoring of fibrogenesis in the lung, the heart, where a separate trial in myocardial infarction patients is already underway, and the tumor microenvironment. For MASH in particular, where novel anti-fibrotic drugs are flooding the pipeline and patient stratification remains a major bottleneck, a tracer that quantifies active fibrogenesis could transform how patients are selected for trials and how treatment response is measured, replacing repeated biopsies with a one-hour scan.

Much work remains before [68Ga]Ga-ATH001 reaches routine clinical use. The dosimetry cohort was small, and liver uptake will be explored further in additional participants across different stages of MASH within the ongoing clinical study. Still, the combination of favorable dosimetry, clean safety data and demonstrable discrimination between healthy and fibrotically active livers gives the tracer a strong foundation for the next phase of development. If subsequent studies confirm its diagnostic accuracy, clinicians may soon gain what they have lacked for decades: a repeatable, quantitative window into the scarring process itself, caught early enough to do something about it.

Subject of Research: First-in-human biodistribution and radiation dosimetry of the PDGFRβ-targeting PET tracer [68Ga]Ga-ATH001 for imaging active fibrosis

Article Title: Biodistribution and radiation dosimetry of the PDGFRβ targeting PET tracer [68Ga]Ga-ATH001

Article References: Lubberink, M., Lohith, T. G., Derdak, Z., Wilkens, P., Palmér, E., Ramolli, A., Ferrat, M., Tran, T. A., Mitran, B., Abouyzayed, A., Johansson, L., Wennbo, H., Rorsman, F., Vessby, J., & Eriksson, O. (2026). Biodistribution and radiation dosimetry of the PDGFRβ targeting PET tracer [68Ga]Ga-ATH001. European Journal of Nuclear Medicine and Molecular Imaging. https://doi.org/10.1007/s00259-026-08167-9

Image Credits: AI Generated

DOI: 10.1007/s00259-026-08167-9

Keywords: PET imaging, PDGFRβ, fibrosis, radiation dosimetry, Affibody molecule, gallium-68, MASH, liver fibrogenesis, hepatic stellate cells, first-in-human study, molecular imaging, radiotracer safety

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