Multiple signaling pathways involved in stimulation of osteoblast differentiation by N-methyl-D-aspartate receptors activation in vitro

Abstract

Aim: Glutamate receptors are expressed in osteoblastic cells. The present study was undertaken to investigate the mechanisms underlying the stimulation of osteoblast differentiation by N-methyl-D-aspartate (NMDA) receptor activation in vitro. Methods: Primary culture of osteoblasts was prepared from SD rats. Microarray was used to detect the changes of gene expression. The effect of NMDA receptor agonist or antagonist on individual gene was examined using RT-PCR. The activity of alkaloid phosphotase (ALP) was assessed using a commercial ALP staining kit. Results: Microarray analyses revealed that 10 genes were up-regulated by NMDA (0.5 mmol/L) and down-regulated by MK801 (100 μmol/L), while 13 genes down-regulated by NMDA (0.5 mmol/L) and up-regulated by MK801 (100 μmol/L). Pretreatment of osteoblasts with the specific PKC inhibitor Calphostin C (0.05 μmol/L), the PKA inhibitor H-89 (20 nmol/L), or the PI3K inhibitor wortmannin (100 nmol/L) blocked the ALP activity increase caused by NMDA (0.5 mmol/L). Furthermore, NMDA (0.5 mmol/L) rapidly increased PI3K phosphorylation, which could be blocked by pretreatment of wortmannin (100 nmol/L). Conclusion:The results suggest that activation of NMDA receptors stimulates osteoblasts differentiation through PKA, PKC, and PI3K signaling pathways, which is a new role for glutamate in regulating bone remodeling.

The Role of NMDA Receptors in Alzheimer’s Disease

“…Uncontrolled glutamate levels in brain are toxic to neurons, damage endothelial function and disrupt BBB integrity (András et al, 2007; Basuroy et al, 2013). Osteoblast NMDARs stimulated precursor differentiation and contributed to increased bone mineralization, leading to bone matrix deposition (Hinoi et al, 2003; Li et al, 2011). Renal NMDAR activity stimulated vasodilation in the glomerulus, thereby influencing renal blood flow, filtration, and reabsorption in the proximal tubule (Deng and Thomson, 2009; Anderson et al, 2011; Sproul et al, 2011).…”

Physiological Roles of Non-Neuronal NMDA Receptors

“…In bone, NMDAR expression has been observed in osteoblasts and osteoclasts, with indications they influence dynamic bone remodeling. Osteoblast NMDARs stimulated precursor differentiation and contributed to increased bone mineralization [78], leading to bone matrix deposition [79]. In osteoclasts, NMDAR loss of function led to apoptosis [80] and reduced differentiation [81], suggesting that NMDARs likely contribute to bone resorption [82].…”

Novel NMDA receptor modulators: an update

“…Enhancement of NMDA receptor activity has been suggested to have therapeutic benefit in a range of neurological conditions, including schizophrenia, anxiety, and bone disorders [75,96,127]. Several endogenous compounds including polyamines and neurosteroids have been reported to positively modulate the NMDA receptor complex [7,25,128,129].…”