Mural Cell SRF Controls Pericyte Migration, Vessel Patterning and Blood Flow

Abstract

Background: Pericytes and vascular smooth muscle cells, collectively known as mural cells, are recruited through PDGFB (platelet-derived growth factor B)-PDGFRB (platelet-derived growth factor receptor beta) signaling. MCs are essential for vascular integrity, and their loss has been associated with numerous diseases. Most of this knowledge is based on studies in which MCs are insufficiently recruited or fully absent upon inducible ablation. In contrast, little is known about the physiological consequences that result from impairment of specific MC functions. Here, we characterize the role of the transcription factor SRF (serum response factor) in MCs and study its function in developmental and pathological contexts. Methods: We generated a mouse model of MC-specific inducible Srf gene deletion and studied its consequences during retinal angiogenesis using RNA-sequencing, immunohistology, in vivo live imaging, and in vitro techniques. Results: By postnatal day 6, pericytes lacking SRF were morphologically abnormal and failed to properly comigrate with angiogenic sprouts. As a consequence, pericyte-deficient vessels at the retinal sprouting front became dilated and leaky. By postnatal day 12, also the vascular smooth muscle cells had lost SRF, which coincided with the formation of pathological arteriovenous shunts. Mechanistically, we show that PDGFB-dependent SRF activation is mediated via MRTF (myocardin-related transcription factor) cofactors. We further show that MRTF-SRF signaling promotes pathological pericyte activation during ischemic retinopathy. RNA-sequencing, immunohistology, in vivo live imaging, and in vitro experiments demonstrated that SRF regulates expression of contractile SMC proteins essential to maintain the vascular tone. Conclusions: SRF is crucial for distinct functions in pericytes and vascular smooth muscle cells. SRF directs pericyte migration downstream of PDGFRB signaling and mediates pathological pericyte activation during ischemic retinopathy. In vascular smooth muscle cells, SRF is essential for expression of the contractile machinery, and its deletion triggers formation of arteriovenous shunts. These essential roles in physiological and pathological contexts provide a rationale for novel therapeutic approaches through targeting SRF activity in MCs.

Stromal netrin-1 coordinates renal arteriogenesis and mural cell differentiation

“…Recruitment of mural cells profoundly impacts vascular integrity and vascular function, and has more recently been implicated in vascular patterning (Armulik et al, 2011;Gaengel et al, 2009;Kemp et al, 2022;Orlich et al, 2022;Stratman et al, 2017). In this study, we show that ablation of a renal stromal factor, Ntn1, influences behavior and differentiation of the renal mural cells.…”

“…In mature vessels, mural cells regulate a host of vascular properties, including vessel patency, quiescence, and tone, as they are exposed to shear stress and pressure from hemodynamic flow. Mural cells have also recently been proposed to regulate the patterning and development of vasculature (Orlich et al, 2022;Stratman et al, 2017).…”

Nitric oxide synthase and reduced arterial tone contribute to arteriovenous malformation

“…Supporting this hypothesis, ex vivo data in isolated mesenteric arteries from HHT type 1 heterozygous knockout mice ( 33 ) and computational modeling ( 34 ) suggest that compromised vascular tone contributes to HHT pathology. In addition, mice lacking serum response factor in smooth muscle cells lose contractile protein expression and develop retinal AV shunts ( 35 ). However, direct measurement of impaired arterial tone in animals that develop AVMs has been lacking.…”

“…Somatic activating mutations in KRAS ( KRASG12V ) were recently identified, with high prevalence in brain AVM patient samples ( 8 , 35 ). The link between KRAS and Notch is currently under investigation.…”

Age-associated changes in endothelial transcriptome and chromatin landscape correlate with elevated risk of hemorrhage

“…The presence of continuous tight junctions (TJs) that form a physical barrier between the ECs, the adherens junctions (AJs), and the basement membrane (BM) are the major structures that impart on the cerebral microvasculature its unique characteristic of BBB function 9,10 . Cytoskeletal activities and cell-cell interactions of ECs are regulated to an important extent by the transcription factor SRF [11][12][13][14][15] . In this study, however, we did not impair SRF activity experimentally, but rather asked whether the aging process impinges on BBB function, potentially via modulating endogenous SRF activity.…”