Intestinal Epithelial-like Cells Stimulated by a Functional Food Ingredient Promote Lysyl Oxidase (LOX) Expression in Osteoblast Precursor Cells via BMP-1 Secretion

Osteoporosis is characterized by reductions in bone mineral density (BMD) and bone quality. While gut-derived signaling has been increasingly studied in relation to BMD, its contribution to molecular factors associated with bone quality remains less defined. Here, we investigated whether a heat-inactivated, freeze-dried, non-viable preparation of Levilactobacillus brevis AS-1 modulates intestinal epithelial-like cells and thereby promotes lysyl oxidase (LOX), a key enzyme involved in collagen cross-linking. Caco-2 cells were treated using 1 mM sodium butyrate and subsequently stimulated with 100 μg/mL L. brevis AS-1. Supernatants were collected and applied to MG63 cells. Cytokine mRNA expression in Caco-2 cells and LOX responses in MG63 cells were analyzed by qRT-PCR, and bone morphogenetic protein (BMP-1) and transforming growth factor-β (TGF-β)1 protein levels in the supernatant were measured by ELISA. L. brevis AS-1 stimulation up-regulated BMP-1 and TGF-β1 mRNA expression in SB-treated Caco-2 cells and increased BMP-1 protein secretion into the supernatant. LOX mRNA expression and total LOX activity were increased in MG63 cells treated with the conditioned supernatant, and inhibition of BMP-1/procollagen C-proteinase activity (UK383367) attenuated LOX mRNA induction. Collectively, these results suggest that L. brevis AS-1 stimulates intestinal epithelial-like cells to secrete BMP-1, which in turn promotes LOX mRNA expression in osteoblast precursor cells. This in vitro mechanism supports the concept of gut–bone crosstalk regulating molecular factors associated with bone quality.