PRDM16 supports Fibro-Adipogenic Progenitors regenerative competence by coupling heterochromatin architecture to Mitotic Fidelity

Fibro-adipogenic progenitors (FAPs) are muscle-resident mesenchymal multipotent cells essential for skeletal muscle homeostasis and regeneration. Upon injury, FAPs rapidly expand to support muscle stem cell function and tissue repair. However, how their proliferative competence is maintained during regeneration remains poorly understood. Here, we identified Prdm16 as a critical regulator of FAPs’ mitotic fidelity. In FAPs, Prdm16 localizes to the NL where it anchors H3K9-methylated chromatin. Loss of Prdm16 disrupts peripheral heterochromatin tethering and triggers severe nuclear lamina defects, such as invaginations, blebbing and envelope ruptures. Notably, these abnormalities become particularly evident upon injury-induced proliferation, suggesting that Prdm16 is required to preserve nuclear integrity under proliferative stress. Consistent with this model, Prdm16-deficient FAPs display profound mitotic defects, including impaired mitotic progression, cytokinesis failure, micronuclei formation and accumulation of tetraploid/aneuploid cells. In vivo, these defects hamper injury-induced expansion of FAPs, culminating with impaired muscle regeneration. Mechanistically, we further show that loss of Prdm16 alters H3K9me2 genomic distribution, reducing its occupancy over gene-associated regions while increasing it at both peri-centromeric and centromeric regions. Together, these data identify Prdm16 as a previously unrecognized factor important to maintain FAPs’ mitotic fidelity by preserving the correct spatial patterning of heterochromatin.