<p>Skeletal muscle tissue consists of not only myofibers, i.e., muscle cells, but also intramuscular adipocytes. Our previous study demonstrated that adipocytes produce secretory factors during differentiation, leading us to hypothesize that soluble factors derived from adipocytes regulate gene expression and cellular function in muscle cells. Yet the mechanism by which coexisting adipocytes influence muscle cells remains unclear. Here, microarray analysis was used to examine transcriptional changes in muscle cells under two co-culture conditions: myoblasts co-cultured with differentiated adipocytes and myotubes co-cultured with preadipocytes. Gene Ontology terms related to cell adhesion, extracellular matrix (ECM) organization, and metabolic processes were significantly enriched in both conditions. We also assessed the influence of adipocyte co-culture on myogenic differentiation and fiber type-specific gene expression. In myoblasts, co-culture with differentiated adipocytes had no significant effect on the expression of myogenic regulatory factors, whereas Myh2 and Myh4 expression was markedly increased in myotubes co-cultured with preadipocytes. These results indicate that adipocyte-derived soluble factors alter the transcriptional landscape of muscle cells, especially genes involved in ECM remodeling and metabolic regulation. This intercellular communication likely contributes to structural and metabolic adaptations in skeletal muscle tissue in vivo.</p>