CD5L promotes efferocytosis and resolution of retinal ischemic injury

Ischemia-induced retinopathy is a defining feature of prevalent ocular conditions, including diabetic retinopathy and central retinal artery or vein occlusion. Therapeutic interventions for ischemic retinopathies show limited efficacy and adverse effects, highlighting the need to thoroughly investigate the underlying mechanisms. Histone deacetylase 3 (HDAC3), a member of the histone deacetylase family, plays a central role in regulating gene expression in myeloid cells (microglia and macrophages). We recently showed that myeloid HDAC3 deletion promotes tissue repair and functional recovery after retinal ischemia-reperfusion (IR) injury via efferocytosis, a process by which myeloid cells engulf and clear apoptotic cells. Here, we investigated the mechanism by which myeloid HDAC3 deletion enhances efferocytosis. Employing an in vitro efferocytosis assay coupled with RNA sequencing on HDAC3 KO macrophages revealed that the secreted protein, CD5 molecule-like (CD5L), was the most upregulated among other pro-efferocytic genes. In vivo, we found that CD5L levels markedly increased in the retinas of myeloid HDAC3 KO mice subjected to IR injury, and its expression colocalized with myeloid cells. Co-immunoprecipitation experiments showed that HDAC3 represses CD5L expression in a liver X receptor (LXRα)-dependent manner. Additionally, we found that CD36, a receptor for CD5L that facilitates the clearance of apoptotic cells, was upregulated in retinal myeloid cells after IR. In vitro, CD5L treatment enhanced efferocytosis via CD36. We then evaluated the role of CD5L in retinal IR injury using in vivo neuronal, vascular, structural, and functional endpoints. CD5L KO mice showed worsened outcomes after IR, whereas treatment with recombinant CD5L was protective against retinal ischemic injury. Collectively, our findings suggest that deleting HDAC3 enhances macrophage efferocytosis by upregulating the CD5L/CD36 axis. CD5L may serve as a promising therapeutic target to improve outcomes in ischemic retinopathy.