The splicing factor kinase SRPK1 is a therapeutic target for Peripheral Vascular Disease

VEGF-A splicing has been shown to be regulated in cancer and epithelial cells by phosphorylation of serine/arginine splicing factor 1 (SRSF1) by serine-arginine protein kinase 1 (SRPK1). In these cell types inhibition of SRPK1 switches splicing to the anti-angiogenic VEGF-A isoforms. In peripheral arterial disease (PAD) the anti-angiogenic isoform of VEGF-A, VEGF-A165b, is overexpressed in circulating monocytes. To determine control of VEGF splicing in monocytes, we investigated the effects of SRPK1 inhibition and monocyte-specific SRPK1 knockout in mouse models of PAD and in human monocytes from patients with PAD. Methods: VEGF-A165b activity was measured in monocytes from patients with PAD by co-culture with endothelial cells in a migration assay in the presence of SRPK1 inhibitors. Mice with impaired revascularisation due to either soluble frizzled related protein 5 knockout (Sfrp5-/-), monocyte-specific gain-of-function of Wnt5a (LysM-Wnt5aGOF), or obese mice on a high fat high sucrose (HF/HS) diet were subjected to femoral artery ligation and treated with SRPK1 inhibitor SPHINX31. To determine monocyte specific SRPK1 activity we generated an SRPK1 conditional knockout under control of a monocyte specific (LysM-Cre) driver (SRPK1MoKO). Paw blood flow was measured by Laser Speckle Imaging before, and for 28 days after, surgery. Results: Monocytes from patients with PAD significantly inhibited migration of human endothelial cells in culture, which was inhibited by an anti-VEGF-A165b antibody. Surprisingly, this inhibition was reversed by SRPK1 inhibition, which switched splicing from VEGF-A165b to VEGF-A165a. In the Sfrp5-/-, LysM-Wnt5aGOF and HF/HS mouse models of PAD, impaired blood flow was reversed by SRPK1 inhibition. The impaired revascularisation in LysM-Wnt5aGOF mice was also rescued in LysM-Wnt5aGOF:SRPK1MoKO mice. Impaired blood flow recovery was also rescued in obese-SRPK1MoKO mice. Conclusion: VEGF splicing in monocytes is differently regulated from VEGF splicing in epithelial cells or cancer cells. This indicates that control of splicing is dependent on cell type and/or environment. SRPK1 inhibition is able to enhance collateralisation in mice, and in vitro models of monocyte dependent impaired angiogenesis in human endothelial cells. ### Competing Interest Statement JCM, SJH, and JB and DOB hold equity in companies that are making SRPK1 inhibitors for clinical use. DOB and SJH hold equity in companies that are making antibodies to VEGF165b for clinical use.