The emerging role of NPNT in tissue injury repair and bone homeostasis.

Nephronectin (NPNT), a highly conserved extracellular matrix protein, plays an important role in regulating cell adhesion, differentiation, spreading, and survival. NPNT protein belongs to the epidermal growth factor (EGF)-like superfamily and exhibits several common structural determinants; including EGF-like repeat domains, MAM domain (Meprin, A5 Protein, and Receptor Protein-Tyrosine Phosphatase µ), RGD motif (Arg-Gly-Asp) and a coiled-coil domain. It regulates integrins-mediated signaling pathways via the interaction of its RGD motif with integrin α8β1. Recent studies revealed that NPNT is involved in kidney development, renal injury repair, atrioventricular canal differentiation, pulmonary function, and muscle cell niche maintenance. Moreover, NPNT regulates osteoblast differentiation and mineralization, as well as osteogenic angiogenesis. Altered expression of NPNT has been linked with the progression of certain types of cancers, such as spontaneous breast tumor metastasis and malignant melanoma. Interestingly, NPNT gene expression can be regulated by a range of external factors such as tumor necrosis factor alpha (TNF-α), transforming growth factor beta (TGF-β), oncostatin M (OSM), bone morphogenic protein 2 (BMP2), Wnt3a, Vitamin D3 , and microRNA-378 (miR378). Further understanding the cellular and molecular mechanisms by which NPNT regulates tissue homeostasis in an organ-specific manner is critical in exploring NPNT as a therapeutic target for tissue regeneration and tissue engineering.