A Soluble Platelet-Derived Growth Factor Receptor-fi Originates via Pre-mRNA Splicing in the Healthy Brain and Is Upregulated during Hypoxia and Aging

The platelet-derived growth factor-BB (PDGF-BB) pathway provides critical regulation of cerebrovascular pericytes, orchestrating their investment and retention within the brain microcirculation. Dysregulated PDGF Receptor-beta (PDGFR beta) signaling can lead to pericyte defects that compromise blood-brain barrier (BBB) integrity and cerebral perfusion, impairing neuronal activity and viability, which fuels cognitive and memory deficits. Receptor tyrosine kinases such as PDGF-BB and vascular endothelial growth factor-A (VEGF-A) are often modulated by soluble isoforms of cognate receptors that establish signaling activity within a physiological range. Soluble PDGFR beta (sPDGFR beta) isoforms have been reported to form by enzymatic cleavage from cerebrovascular mural cells, and pericytes in particular, largely under pathological conditions. However, pre-mRNA alternative splicing has not been widely explored as a possible mechanism for generating sPDGFR beta variants, and specifically during tissue homeostasis. Here, we found sPDGFR beta protein in the murine brain and other tissues under normal, physiological conditions. Utilizing brain samples for follow-on analysis, we identified mRNA sequences corresponding to sPDGFR beta isoforms, which facilitated construction of predicted protein structures and related amino acid sequences. Human cell lines yielded comparable sequences and protein model predictions. Retention of ligand binding capacity was confirmed for sPDGFR beta by co-immunoprecipitation. Visualizing fluorescently labeled sPDGFR beta transcripts revealed a spatial distribution corresponding to murine brain pericytes alongside cerebrovascular endothelium. Soluble PDGFR fi protein was detected throughout the brain parenchyma in distinct regions, such as along the lateral ventricles, with signals also found more broadly adjacent to cerebral microvessels consistent with pericyte labeling. To better understand how sPDGFR beta variants might be regulated, we found elevated transcript and protein levels in the murine brain with age, and acute hypoxia increased sPDGFR beta variant transcripts in a cell-based model of intact vessels. Our findings indicate that soluble isoforms of PDGFR beta likely arise from pre-mRNA alternative splicing, in addition to enzymatic cleavage mechanisms, and these variants exist under normal physiological conditions. Follow-on studies will be needed to establish potential roles for sPDGFR beta in regulating PDGF-BB signaling to maintain pericyte quiescence, BBB integrity, and cerebral perfusion-critical processes underlying neuronal health and function, and in turn, memory and cognition.

Automated summary

The platelet-derived growth factor-BB (PDGF-BB) pathway crucially regulates cerebrovascular pericytes, affecting blood-brain barrier (BBB) integrity and cerebral perfusion. Soluble isoforms of the PDGF receptor-beta (sPDGFR beta) have been found in the brain and other tissues under normal physiological conditions. These isoforms are likely generated through pre-mRNA alternative splicing, in addition to enzymatic cleavage mechanisms. sPDGFR beta variants may play a role in maintaining pericyte quiescence, BBB integrity, cerebral perfusion, and neuronal health and function, influencing memory and cognition.