Angiopoietin-Like 4 Induces Upregulation of VEGF and sVCAM1 Through JNK/c-Jun and JAK2/STAT5 Signaling Pathways

Purpose: Angiopoietin-like protein 4 (ANGPTL4) is a multifunctional cytokine regulating angiogenesis, vascular permeability, and inflammation that is elevated, along with vascular endothelial growth factor (VEGF), in multiple ocular neovascular disorders, including ischemic retinopathies and neovascular age-related macular degeneration. However, the downstream signaling pathways that contribute to the effects of ANGPTL4 in ocular disease remain unclear. Methods: A phospho-kinase Proteome Profiler array was used to map pathways activated by recombinant ANGPTL4 in immortalized murine retinal endothelial cells (iRECs). Candidate signaling routes were assessed using pharmacologic inhibition and siRNA-mediated knockdown to define their roles in ANGPTL4-driven angiogenesis and effector upregulation. Findings were validated following intraocular ANGPTL4 delivery in C57BL/6J mice. Results: ANGPTL4 robustly activated the c-Jun N-terminal kinase (JNK)/c-Jun and Janus kinase 2 (JAK2)/signal transducer and activator of transcription 5 (STAT5) axes in iRECs, a signature recapitulated in neurosensory retina in vivo. Inhibition of either pathway significantly reduced ANGPTL4-induced angiogenesis, identifying these pathways as critical effectors of ANGPTL4 signaling. ANGPTL4 induced secretion of VEGF, soluble vascular cell adhesion molecule 1 (sVCAM1), T-cell immunoglobulin and mucin domain 1 (TIM-1), and proliferin; however, only VEGF and sVCAM1 depended on JNK/c-Jun and JAK2/STAT5. Conclusions: ANGPTL4 functions as a signaling hub that integrates different cues to activate JNK/c-Jun and JAK2/STAT5 and upregulate the expression of key pathogenic proteins including VEGF and sVCAM1. This work establishes these cascades as previously unrecognized effectors of ANGPTL4 signaling in the retina and brings important insight into the critical role that ANGPTL4 plays in neovascular retinal disease.