Bioenergetics and mitochondrial transmembrane potential during differentiation of cultured osteoblasts

Abstract

To evaluate the relationship between osteoblast differentiation and bioenergetics, cultured primary osteoblasts from fetal rat calvaria were grown in medium supplemented with ascorbate to induce differentiation. Before ascorbate treatment, the rate of glucose consumption was 320 nmol. h(-1). 10(6) cells(-1), respiration was 40 nmol. h(-1). 10(6) cells(-1), and the ratio of lactate production to glucose consumption was approximately 2, indicating that glycolysis was the main energy source for immature osteoblasts. Ascorbate treatment for 14 days led to a fourfold increase in respiration, a threefold increase in ATP production, and a fivefold increase in ATP content compared with that shown in immature cells. Confocal imaging of mitochondria stained with a transmembrane potential-sensitive vital dye showed that mature cells possessed abundant amounts of high-transmembrane-potential mitochondria, which were concentrated near the culture medium-facing surface. Acute treatment of mature osteoblasts with metabolic inhibitors showed that the rate of glycolysis rose to maintain the cellular energy supply constant. Thus progressive differentiation coincided with changes in cellular metabolism and mitochondrial activity, which are likely to play key roles in osteoblast function.

AMP-activated protein kinase pathway and bone metabolism

“…This may be due to the high energy requirements and therefore elevated ATP contents observed in mature osteoblasts during bone matrix production and mineralization. Osteoblast differentiation was previously shown to coincide with changes in cellular metabolism and mitochondrial activity (Komarova et al 2000). In agreement with this, our results demonstrate that when AICAR and metformin were added to primary osteoblasts at specific stages of their differentiation, although they always induced AMPK phosphorylation, their effects were more potent at later stages of osteoblastic differentiation (unpublished results, M Shah, J Jeyabalan, B Viollet & C Chenu).…”

IGF-1 regulation of key signaling pathways in bone

“…Whereas during osteoblast differentiation when the cells have more need for energy consumption and need to synthesize more protein, there is an increase in mitochondrial transmembrane potential and the cells switch over to oxidative phosphorylation in tune with their differentiation status. 57 The effects of IGF-1 on mitochondrial function during both chondrogenic differentiation and osteogenic differentiation may be particularly important. These observations lead to a number of questions that require answers: (1) what are the energy requirements of MSC, which have the potential to differentiate into a number of different lineages?…”

Nanofiber scaffolds influence organelle structure and function in bone marrow stromal cells

“…Osteogenic differentiation may also be concomitant with a shift to oxidative phosphorylation, 62 despite the high energy demands of fabricating a bony, mineralized extracellular. Peroxisomes contain 50 or more enzymes and play a key role in fatty acid catabolism.…”