Peripheral arterial disease (PAD) is a worldwide disease caused by atherosclerosis. It is a circulatory condition where narrowed blood vessels reduce blood flow to the peripheral such as legs. Although current gold standard treatment for advanced PAD patients is still based on surgical revascularization, there is no effective therapy for many patients that are not suitable for surgery. In addition, better recovery from surgical revascularization largely relies on angiogenesis in the adjacent ischemic tissue. Thus, novel pro-angiogenic therapies to improve post-ischemic neovascularization are urgently desired. However, current poor understanding of the roles of anti-inflammatory cytokines in angiogenesis prevents the development of these new therapies. We and others have reported that IL-35 is a newly identified inducible immunosuppressive heterodimeric cytokine in the IL-12 family. IL-35 is composed of p35 (IL-12A) and EBI3, and its receptors are comprised of homodimers or heterodimer of IL-12Rb2 and gp130 (IL-6ST). We have shown that IL-35 inhibits endothelial cell (EC) activation induced by lipopolysaccharide (LPS) or atherogenic lysophosphatidylcholine (LPC). At least partially through these new EC-dependent mechanisms, IL-35 inhibits inflammation in autoimmune diseases, infectious diseases, atherosclerosis, and tumors. Recent studies have indicated the role of IL-35 in angiogenesis in rheumatoid arthritis and different tumors. However, whether and how IL-35 regulates post-ischemic angiogenesis in peripheral artery disease are unrevealed. In our study, we used hindlimb ischemia (HLI) and Matrigel plug assay as in vivo angiogenesis models and wound healing assay as in vitro angiogenesis model to study the role and underlying mechanisms of IL-35-mediated angiogenesis. We made the following findings: 1) muscle in human and mouse has high angiogenic potential in physiological conditions; 2) angiogenic cytokines and chemokines including anti-inflammatory cytokines are predominantly regulated by inflammatory transcription factors; 3) IL-35 signaling is induced in ischemic muscle; 4) IL-12Rb2, but not IL-6ST, is the key receptor component of IL-35 signaling in ischemic muscle and hypoxic human microvascular endothelial cells (HMVECs); 5) hyperlipidemia (atherogenic factor) impairs angiogenesis in vivo and in vitro, which partially acts through the induction of IL-35; 6) IL-12Rb2 deficiency improves HLI-induced angiogenesis in both WT or apolipoprotein E (ApoE) -/- mice (an atherosclerosis model); 7) IL-35 injection inhibits HLI-induced angiogenesis in WT mice but not that in the IL-12Rb2 deficient mice; 8) IL-35 injection enlarges the avascular area in gastrocnemius muscle after HLI; 9) IL-35 obstructs fibroblast growth factor-2 (FGF2)-induced angiogenesis in Matrigel plug assay in vivo; 10) CD45-CD31+ ECs from the IL-35-injected ischemic muscle at day 14 of HLI have an abnormal extracellular matrix organization, activated integrin pathways (cell-matrix adhesions), disrupted vascular endothelial (VE)-cadherin-plakoglobin complex (cell-cell adhesions), and increased infiltration and migration of bone marrow-derived leukocytes; 11) IL-35 inhibits HMVEC migration in wound healing assay in vitro presumably through upregulation of anti-angiogenic proteins including pigment epithelium-derived factor (PEDF), serpin family B member 5 (SERPINB5, Maspin), and thrombospondin (THBS)-1. These results suggest that anti-inflammatory cytokine IL-35, signaling through the key receptor subunit IL-12Rb2, inhibits HLI-induced angiogenesis and delays tissue repair by dysregulating cell-cell and cell-matrix adhesions, which leads to the impaired vascular adhesion junction and maturation of blood vessels. / Biomedical Sciences