RUNX2 and osteoporosis: The down-regulation of runt-related transcription factor 2 (Runx2) and osterix expression, as well as the up-regulation of peroxisome proliferation-activated receptor γ (PPARγ) expression in MSCs, which are important in regulating osteogenic and adipogenic differentiation, inhibit bone formation and increase adipose accumulation, resulting in osteoporosis (Fig. 2) [2, 24, 25].