Mechanical strain-induced NO production by bone cells: a possible role in adaptive bone (re)modeling?

Abstract

The structural competence of the skeleton is maintained by an adaptive mechanism in which resident bone cells respond to load-induced strains. To investigate the possible role of the messenger molecule nitric oxide (NO) in this response, we studied NO production in well-characterized organ culture systems, rat long bone-derived osteoblast-like (LOBs) cells, and embryonic chick osteocytes (LOCYs) in monolayer culture. In superfused cancellous bone cores, loading (for 15 min) produces increases in NO2- (stable NO metabolite) release during the loading period, which paralleled those in PGI2 and PGE2. Loading of rat vertebrae and ulnae produces increases in NO2- release, and in ulnae NO synthase inhibitors diminish these responses. Transient rapid increases in NO release are stimulated by strain in both LOBs and LOCYs. Polymerase chain reaction amplification of extracted mRNA shows that rat ulnae, LOBs, and LOCYs express both the inducible and neuronal (constitutive) isoforms of NO synthase. Adaptability to mechanical strain relies on assessment of the strain environment followed by modification of bone architecture. Immediate increases in NO production induced by loading suggest the involvement of NO in strain measurement and cellular communication to establish strain distribution, as well as potentially in adaptive changes in bone cell behavior.

Expression of Functional Metabotropic Glutamate Receptors in Primary Cultured Rat Osteoblasts

“…Cells cultured as described above have been shown to stain positive for alkaline phosphatase and osteocalcin and to produce mineralized matrix (22). We have confirmed osteoblastic phenotype by staining for alkaline phosphatase and using Western blots and radioimmunoassay to demonstrate expression of osteopontin and osteocalcin (23,24).…”

“…Cell Culture-Cultures of rat femoral osteoblasts were prepared similarly to the method of Pitsillides et al (22). Rats (120 -130 g) were killed by cervical dislocation.…”

Endothelial Nitric Oxide Synthase Gene-Deficient Mice Demonstrate Marked Retardation in Postnatal Bone Formation, Reduced Bone Volume, and Defects in Osteoblast Maturation and Activity

“…NO synthesized by eNOS [17][18][19][20][21][22][23][24] and also iNOS 9 -16 is strongly implicated in the regulation of bone metabolism exerting powerful effects on cells of both the osteoblast and osteoclast lineage. However, the specific functional roles of these enzymes in these cells and their effects on bone turnover are not clearly defined.…”

“…18 These observations have demonstrated that the synthesis and activity of both eNOS and iNOS is significant in bone biology although there is consensus that under physiological conditions eNOS probably represents the major NOS activity regulating bone formation. [17][18][19][20][21][22][23][24] Despite this, many of the previous studies have been based on the use of NOS inhibitors and are therefore subject to potential inconsistencies arising from the lack of isoformspecific selectivity of these compounds as well as effects independent of NOS inhibition. 4,29 Consequently, it has not been previously possible to define clearly the contribution made by a specific NOS isoform to the control of bone turnover.…”

Aseptic Loosening Of Total Hip Replacement: Macrophage Expression Of Inducible Nitric Oxide Synthase And Cyclo-oxygenase-2, Together With Peroxynitrite Formation, As A Possible Mechanism For Early Prosthesis Failure

“…16 Furthermore, cytokine-induced NO synthesis is also involved in the induction of apoptosis, or programmed cell death, in osteoblast cultures. 32 Pitsillides et al 33 have shown that physiological levels of mechanical strain can induce NO production within a few minutes of application of the strain. This rapid NO production implies the presence of a constitutive form of NOS within the bone cells and our recent studies have indeed shown that eNOS isoform is present in osteoblasts, osteocytes and osteoclasts.…”