Infection of Brain Pericytes Underlying Neuropathology of COVID-19 Patients

A wide range of neurological manifestations have been associated with the development of COVID-19 following SARS-CoV-2 infection. However, the etiology of the neurological symptomatology is still largely unexplored. Here, we used state-of-the-art multiplexed immunostaining of human brains (n = 6 COVID-19, median age = 69.5 years; n = 7 control, median age = 68 years) and demonstrated that expression of the SARS-CoV-2 receptor ACE2 is restricted to a subset of neurovascular pericytes. Strikingly, neurological symptoms were exclusive to, and ubiquitous in, patients that exhibited moderate to high ACE2 expression in perivascular cells. Viral dsRNA was identified in the vascular wall and paralleled by perivascular inflammation, as signified by T cell and macrophage infiltration. Furthermore, fibrinogen leakage indicated compromised integrity of the blood–brain barrier. Notably, cerebrospinal fluid from additional 16 individuals (n = 8 COVID-19, median age = 67 years; n = 8 control, median age = 69.5 years) exhibited significantly lower levels of the pericyte marker PDGFRβ in SARS-CoV-2-infected cases, indicative of disrupted pericyte homeostasis. We conclude that pericyte infection by SARS-CoV-2 underlies virus entry into the privileged central nervous system space, as well as neurological symptomatology due to perivascular inflammation and a locally compromised blood–brain barrier.

Infection of brain pericytes underlying neuropathology of COVID-19 patients

A wide range of neurological manifestations have been associated with the development of COVID-19 following SARS-CoV-2 infection. However, the etiology of the neurological symptomatology is still largely unexplored. Here, we used state-of-the-art multiplexed immunostaining of human brains (n = 6 COVID-19, median age = 69,5 years; and n = 7 control, median age = 68 years), and demonstrated that expression of the SARS-CoV-2 receptor ACE2 is restricted to a subset of neurovascular pericytes. Strikingly, neurological symptoms were exclusive to, and ubiquitous in, patients that exhibited moderate to high ACE2 expression in peri-vascular cells. Viral particles were identified in the vascular wall and paralleled by peri-vascular inflammation, as signified by T cell and macrophage infiltration. Furthermore, fibrinogen leakage indicated compromised integrity of the blood-brain barrier. Notably, cerebrospinal fluid from an additional 16 individuals (n = 8 COVID-19, median age = 67 years; and n = 8 control, median age = 69,5 years) exhibited significantly lower levels of the pericyte marker PDGFRβ in SARS-CoV-2-infected cases, indicative of disrupted pericyte homeostasis. We conclude that pericyte infection by SARS-CoV-2 underlies virus entry into the privileged central nervous system space, as well as neurological symptomatology due to peri-vascular inflammation and a locally compromised blood-brain barrier.

DIPG-33. CHARACTERIZING THE NEURO-VASCULAR UNIT IN DIFFUSE INTRINSIC PONTINE GLIOMA

Diffuse intrinsic pontine glioma (DIPG) is a childhood brainstem tumor with a median overall survival of eleven months. Lack of chemotherapy efficacy may be related to an intact blood-brain-barrier (BBB). In this study we aim to compare the neuro-vascular unit (NVU) of DIPG to healthy pons tissue. End-stage DIPG autopsy samples (n=5) and age-matched healthy pons samples (n=22), obtained from the NIH NeuroBioBank, were immunohistochemically stained for tight-junction proteins claudin-5 and zonula occludens-1 (ZO-1), basement membrane component laminin, and pericyte marker PDGFRβ. Claudin-5 stains were also used to determine vascular density and diameters. In DIPG, expression of claudin-5 and ZO-1 was reduced, and claudin-5 was dislocated to the abluminal side of endothelial cells. Laminin expression at the glia limitans was reduced in both pre-existent vessels and neovascular proliferation. In contrast to healthy pons, no PDGFRβ expression was detected. The number of blood vessels in DIPG was significantly reduced compared to healthy pons, 13.9±11.8/mm2 versus 26.3±14.2/mm2, respectively (P<0.01). Especially the number of smaller blood vessels (<10µm) was significantly lower (P<0.01). Distribution of larger blood vessels (≥10µm) did not differ between groups (P=0.223). Mean vascular diameter was 9.3±9.9µm for DIPG versus 7.7±9.0µm in healthy pons (P=0.016). Our study demonstrates evidence of structural changes in the NVU in end-stage DIPG. Chemotherapeutic inefficacy could be the result of reduced vascular density. However, further research is needed to determine meaning and extent of these changes and to determine whether these observations are caused by the tumor or the result of treatment.

Differing associations between Aβ accumulation, hypoperfusion, blood–brain barrier dysfunction and loss of PDGFRB pericyte marker in the precuneus and parietal white matter in Alzheimer's disease

Recent studies implicate loss of pericytes in hypoperfusion and blood–brain barrier (BBB) leakage in Alzheimer's disease (AD). In this study, we have measured levels of the pericyte marker, platelet-derived growth factor receptor-β (PDGFRB), and fibrinogen (to assess blood–brain barrier leakage), and analyzed their relationship to indicators of microvessel density (von Willebrand factor level), ante-mortem oxygenation (myelin-associated glycoprotein:proteolipid protein-1 ratio and vascular endothelial growth factor level), Aβ level and plaque load, in precuneus and underlying white matter from 49 AD to 37 control brains. There was reduction in PDGFRB and increased fibrinogen in the precuneus in AD. These changes correlated with reduction in oxygenation and with plaque load. In the underlying white matter, increased fibrinogen correlated with reduced oxygenation, but PDGFRB level was unchanged. The level of platelet-derived growth factor-ββ (PDGF-BB), important for pericyte maintenance, was increased in AD but mainly in the insoluble tissue fraction, correlating with insoluble Aβ level. Loss of the PDGFRB within the precuneus in AD is associated with fibrinogen leakage and reduced oxygenation, and related to fibrillar Aβ accumulation. In contrast, fibrinogen leakage and reduced oxygenation of underlying white matter occur independently of loss of PDGFRB, perhaps secondary to reduced transcortical perfusion.

RET mutation and increased angiogenesis in medullary thyroid carcinomas

Advanced medullary thyroid cancers (MTCs) are now being treated with drugs that inhibit receptor tyrosine kinases, many of which involved in angiogenesis. Response rates vary widely, and toxic effects are common, so treatment should be reserved for MTCs likely to be responsive to these drugs.RETmutations are common in MTCs, but it is unclear how they influence the microvascularization of these tumors. We examined 45 MTCs with germ-line or somaticRETmutations (RETmut group) and 34 with wild-typeRET(RETwt). Taqman Low-Density Arrays were used to assess proangiogenic gene expression. Immunohistochemistry was used to assess intratumoral, peritumoral and nontumoral expression levels of VEGFR1, R2, R3, PDGFRa, PDGFB and NOTCH3. We also assessed microvessel density (MVD) and lymphatic vessel density (LVD) based on CD31-positive and podoplanin-positive vessel counts, respectively, and vascular pericyte density based on staining for a-smooth muscle actin (a-SMA), a pericyte marker. Compared withRETwt tumors,RETmut tumors exhibited upregulated expression of proangiogenic genes (mRNA and protein), especially VEGFR1, PDGFB and NOTCH3. MVDs and LVDs were similar in the two groups. However, microvessels inRETmut tumors were more likely to be a-SMA positive, indicating enhanced coverage by pericytes, which play key roles in vessel sprouting, maturation and stabilization. These data suggest that angiogenesis inRETmut MTCs may be more intense and complete than that found inRETwt tumors, a feature that might increase their susceptibility to antiangiogenic therapy. Given their increased vascular pericyte density,RETmut MTCs might also benefit from combined or preliminary treatment with PDGF inhibitors.