Nampt expression increases during osteogenic differentiation of multi- and omnipotent progenitors.
Despite emerging data showing that metabolic changes occur with stem cell differentiation, the cross-talk between factors governing energy metabolism and epigenetic modification is not understood. Nicotinamide adenine dinucleotide (NAD) participates in both energy metabolism and protein modification processes. Changes of the intracellular NAD concentration have been shown to correlate with differentiation of adult and embryonic stem cells. In the present study, we investigated the expression pattern of Nampt, the rate-limiting enzyme in NAD salvaging pathway, during osteogenic differentiation of the multipotent mouse fibroblast C3H10T1/2 and the omnipotent preosteoblast MC3T3-E1 cells. We found that Nampt was increasingly expressed during differentiation in both cell models. The increase of Nampt was associated with higher NAD concentration and Sirt1 activity. Knockdown of Nampt or addition of its specific inhibitor FK866 leads to lower intracellular NAD concentration and decline in osteogenesis. These findings indicate that osteogenic differentiation correlates with intracellular NAD metabolism in which Nampt plays a regulatory role.
Li Y, He J, He X, Li Y…
Biochem. Biophys. Res. Commun. Apr 2013
Involvement of PI3K/Akt/CREB and redox changes in mitochondrial defect of osteoblastic MC3T3-E1 cells.
Antimycin A (AMA) is an inhibitor of mitochondrial electron transport via its binding to complex III. In the present study, the mechanisms involved in AMA-induced cell damage were investigated. Treatment of osteoblastic MC3T3-E1 cells with AMA decreased adenosine 3′,5′-cyclic monophosphate (cAMP) level, activities of phosphoinositide 3-kinase (PI3K) and Akt (protein kinase B), and phosphorylated CREB (cAMP-response element-binding protein).
To examine whether AMA-induced cell damage involves altered metabolism of pyridine nucleotides, the levels of NAD(+), NADH, NADP(+), and NADPH were measured. Treatment with AMA significantly decreased the levels of NAD(+) and NADPH. Moreover, the activities of aconitase and thioredoxin reductase were decreased by AMA treatment. These results suggest that PI3K/Akt/CREB pathway and pyridine nucleotide (NAD(+) and NADPH) are related to mitochondria function of osteoblasts.
Choi EM, Lee YS
Toxicol In Vitro Aug 2011
Extracellular NAD+: a novel autocrine/paracrine signal in osteoblast physiology.
Intercellular communication allows co-ordination of cell metabolism and sensitivity to extracellular stimuli. In bone cells, paracrine stimulation and cell-to-cell coupling through gap junctions induce the formation of complex intercellular networks, which favours the intercellular exchange of nutrients and second messengers, ultimately controlling the process of bone remodelling. The importance of local factors in bone remodelling is known since many years. Bone cells secrete and respond to a variety signals, among which include prostaglandins, cytokines, growth factors, and ATP. We here report evidence that extracellular NAD(+) is a novel extracellular signal stimulating osteoblast differentiation. We found that HOBIT human osteoblastic cells, which are known to express ADP-ribosyl cyclase/CD38 activity, respond to micromolar concentrations of extracellular NAD(+) with oscillatory increases of the cytosolic Ca(2+) concentration. The initial Ca(2+) response was followed by a time-dependent inhibition of cell growth, the appearance of an epithelial morphology, and by an increase of alkaline phosphatase and osteocalcin expression. Under resting condition HOBIT cells release NAD(+) in the extracellular medium and the release is significantly potentiated by mechanical stimulation. Taken together these results point to NAD(+) as a novel autocrine/paracrine factor involved in stimulation and maintenance of the osteoblast differentiated phenotype.
Romanello M, Bicego M, Pirulli D, Crovella S…
Biochem. Biophys. Res. Commun. Dec 2002