Bone remodeling is a crucial process required to re-structure bone tissue according to mechanical needs. The cells directly involved in this process require a significant amount of energy which they primarily obtain from glucose. Within eucaryotic cells, glucose can be metabolized to generate ATP via glycolysis followed by lactate fermentation or by entering the citric acid cycle to fuel oxidative phosphorylation (Oxphos), the process in which mitochondria generate ATP. Both processes' major function is to provide ATP, but also form metabolites used as precursors for amino acids and molecules involved in cell signaling. While the energy turnover in osteoblasts was considered highly glycolytic, recent studies highlight the complexity of cellular metabolism in osteoblast differentiation and the importance of mitochondria, indicated by an Oxphos upregulation after in vitro osteoblast differentiation. In osteoclasts, the upregulation of Oxphos is even more pronounced. The current evidence of the relevance of mitochondrial function to bone metabolism is limited. For instance, a mouse model for T1D (Akita) showed low trabecular and cortical bone mass accompanied by decreased levels of Oxphos and glycolysis in osteoblasts. We speculated that mitochondrial dysfunction would impair bone cell function and hypothesized that mitochondrial respiratory chain deficiency caused by impaired mDNA proofreading decreases osteoblastic differentiation and bone formation capacity. Therefore, we used genomic CRISPR/Cas9 editing to knock-in a variant into the mDNA replicating polymerase gamma A (hMSC-POLGD274A). This was done to disrupt the exonuclease domain of POLG in an MSC line. As expected, we observed a higher number of mDNA mutations and a lower mitochondrial ATP production rate in these cells. Surprisingly, the mitochondrial dysfunction did not result in ATP depletion as this deficit was compensated for by a higher glycolytic ATP production rate. This change in the balance of energy production was also observed in the primary cells of a patient with pathogenic variants in POLG. Moreover, we demonstrated impaired osteoblast differentiation and decreased in vitro bone formation capacity in both the POLG cell model and primary patient cells. This study supports the idea that intact mitochondrial function is required for several key cellular functions.