Immunomodulatory Role of the Stem Cell Circadian Clock in Muscle Repair [RNA-Seq]

The circadian clock orchestrates vital physiological processes such as metabolism, immune function, and tissue regeneration, aligning them with the optimal time of day. This study identifies an intricate interplay between the circadian clock within muscle stem cells (SCs) and their capacity to modulate the immune microenvironment during muscle regeneration. We uncover that the SC clock provokes time-of-day (TOD)-dependent induction in inflammatory response genes following injury, particularly those related to neutrophil activity and chemotaxis. These responses are driven by rhythms of cytosolic regeneration of the signaling metabolite NAD+. We demonstrate that genetically enhancing cytosolic NAD+ regeneration in SCs is sufficient to induce robust inflammatory responses that significantly influence muscle regeneration. Furthermore, using mononuclear single-cell sequencing of the regenerating muscle niche, we uncover a key role for the cytokine CCL2 in mediating SC-neutrophil crosstalk in a TOD-dependent manner. Our findings highlight a crucial intersection between SC metabolic shifts and immune responses within the muscle microenvironment, dictated by the circadian rhythms, and underscore the potential for targeting circadian and metabolic pathways to enhance tissue regeneration. Pax7-zsgreen mice, which were sequentially perfused with 50 ml of ice-cold PBS, followed by 50 ml mild fixative (0.5% paraformaldehyde), and subsequently quenched with 50 ml 2M glycine. SCs were extracted from the hindlimb muscles of Pax7-zsgreen mice, both uninjured and following cardiotoxin-induced injury at ZT16, on day 1 post-injury, and subjected to RNA sequencing for transcriptome analysis.