Impact of proNGF/NGF-NGFR-axis on the regulation of arterial remodelling

Abstract Background Peripheral blood mononuclear cells (MNCs) contribute to the pathogenesis of arteriosclerosis. Nerve growth factor receptor (NGFR) is present in peripheral blood and the ischemic coronary artery. NGFR transduces neurotrophin signals towards cell survival or apoptosis in different cell types dependent on coupling co-receptors. However, the role of NGFR-positive (NGFR+) MNCs in arterial remodelling is unknown. Purpose To investigate the functional mechanisms under which NGFR+ MNCs are involved in arterial remodelling. Methods Adult C57BL/6J male NGFR-wild-type (WT) or -bone marrow (BM)-specific (KO) mice were subjected to unilateral carotid artery ligation. The ligated and the opposite-sided, sham-operated arteries were assessed by immunohistology and gene expression analysis using a PCR on day 28. Also, human NGFR+ MNCs from a healthy volunteer were sorted using fluorescence-activated cell sorting and characterised using RNA sequencing. The cell apoptosis (AnnexinV+7AAD-) and chemotaxis in response to the ligands, NGF and its precursor proNGF, were assessed using flow cytometry and a Transwell migration. Results In WT mice, BM-derived NGFR+ cells accumulated in the neointima after ligation. The neointimal area was significantly greater in the BM-specific depletion of NGFR than in WT mice. NGFR+ cells in the neointima exhibited apoptosis (TUNEL+ and cleaved caspase-3+) accompanied by promoted F4/80+ macrophage and anti-inflammatory IL-10. By contrast, in the BM-specific NGFR-KO model, non-BM-derived SMCs increased in the neointima with augmented proliferation, and the accumulation of BM-derived cells and the expression of IL-10 were decreased. The expressions of proNGF/NGF and inflammatory cytokines, including IL-6, were not changed in a ligated artery, irrespective of NGFR+ depletion. Human NGFR+ MNCs expressed TrkB, TrkC, and sortilin co-receptors but not macrophage markers. Human NGFR+ MNCs, but not NGFR- MNCs, co-cultured with artery SMCs were susceptible to apoptosis in response to proNGF. Additionally, PDGF stimulated proNGF/NGF expression in SMCs, and proNGF/NGF did not affect the proliferation of SMCs in vitro. Furthermore, NGFR+ MNCs, but not NGFR- MNCs, increased migration toward NGF and did not show chemotaxis toward proNGF. Conclusions These data imply that local NGF might draw NGFR+ MNCs to the injured artery, in which proNGF induces NGFR+ MNCs apoptosis. Apoptotic NGFR+ cells promoted macrophage chemotaxis to resolve inflammation and decrease neointimal formation. Thus, we propose the proNGF/NGF-NGFR axis as potentially contributing to the suppression of arterial remodelling.