<i>ZIC1</i> transcription factor overexpression in segmental bone defects is associated with brown adipogenic and osteogenic differentiation

Transcriptional factor regulation is central to the lineage commitment of stem/ progenitor cells. ZIC1 (ZIC family member 1) is a C2H2-type zinc finger transcription factor expressed during development, brown fat, and certain cancers. Previously, we observed that overexpression of ZIC1 induces osteogenic differentiation at the expense of white adipogenic differentiation. In the present study, the feasibility of ZIC1 overexpressed human progenitor cells in critical-sized bone defects was studied. To achieve this, human adipose stem/stromal cells with other without lentiviral ZIC1 overexpression were implanted in a femoral segmental defect model in NOD-SCIDγ mice. Results showed that ZIC1 overexpressed cells induced osteogenic differentiation by protein markers in a critical-sized femoral segment defect compared to empty lentiviral control, although bone union was not observed. The immunohistochemical evaluation showed that implantation of ZIC1 overexpression cells led to an increase in osteoblast antigen expression (RUNX2, OCN), activation of Hedgehog signaling (Patched1), and an increase in brown adipogenesis markers (ZIC1, EBF2). In contrast, no change in bone defect-associated vasculature was observed (CD31, Endomucin). Together, these data suggest that overexpression of the ZIC1 transcription factor in progenitor cells is associated with differentiation towards osteoblastic and brown adipogenic cell fates.