Hydrostatic pressure induces apoptosis in human chondrocytes from osteoarthritic cartilage through up‐regulation of tumor necrosis factor‐α, inducible nitric oxide synthase, p53, c‐myc, and bax‐α, and suppression of bcl‐2

Abstract

Hydrostatic pressure (HP) is thought to increase within cartilage extracellular matrix as a consequence of fluid flow inhibition. The biosynthetic response of human articular chondrocytes to HP in vitro varies with the load magnitude, load frequency, as well as duration of loading. We found that continuous cyclic HP (5 MegaPascals (MPa) for 4 h; 1 Hz frequency) induced apoptosis in human chondrocytes derived from osteoarthritic cartilage in vitro as evidenced by reduced chondrocyte viability which was independent of initial cell densities ranging from 8.1 x 10(4) to 1.3 x 10(6) cells ml(-1). HP resulted in internucleosomal DNA fragmentation, activation of caspase-3, and cleavage of poly-ADP-ribose polymerase (PARP). At the molecular level, induction of apoptosis by HP was characterized by up-regulation of p53, c-myc, and bax-alpha after 4 h with concomitant down-regulation of bcl-2 after 2 h at 5 MPa as measured by RT-PCR. In contrast, beta-actin expression was unchanged. Real-time quantitative RT-PCR confirmed a HP-induced (5 MPa) 1.3-2.6 log-fold decrease in bcl-2 mRNA copy number after 2 and 4 h, respectively, and a significant increase (1.9-2.5 log-fold) in tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) mRNA copy number after 2 and 4 h, respectively. The up-regulation of p53 and c-myc, and the down-regulation of bcl-2 caused by HP were confirmed at the protein level by Western blotting. These results indicated that HP is a strong inducer of apoptosis in osteoarthritic human chondrocytes in vitro.

Altered Chondrocyte Apoptosis Status in Developmental Hip Dysplasia in Rabbits

“…Next, we performed western blot analysis of several apoptosis related proteins. Previous studies have demonstrated that the expression of Bcl-2 plays an apoptosis-inhibiting role, whereas the expression of Bax plays a contrary role (19,20). survival of the cells.…”

Normal delivery induced stress alters glutathione peroxidase and TNF-α in elderly primigravidas mononuclear cells

“…This in turn, renders the glutathione in vivo somewhat semifunctional or defective, and consequently rendering the cells sensitive to inflammatory cytokines such as tumor necrosis factor alpha. The elevations of TNF-α are known to activate and increase a variety of in vivo cellular mechanisms by stimulating NF-κB (1,10,11). It may be noteworthy to point out here that our data showing enhanced GPx activity after 14 days of post delivery, is strongly suggestive for the possible fact that 14 days of time is sufficient enough to arrest the cellular activation of TNF-α and ROS in monocytes by probably ameliorating glutathione by self-defense mechanisms in vivo, consequently resulting in the down-regulation of TNF-α expression in mononuclear cells.…”

“…Humans under stress of any kind are known to generate free radicals like reactive oxygen species (ROS) and reactive nitrogen intermediates (1,2). The function of antioxidant enzymes is to protect cells from toxic oxygen.…”

Chondrocyte Apoptosis: Implications for Osteochondral Allograft Transplantation

“…The gaseous signaling molecule nitric oxide (NO) appears to be a dominant proapoptotic stimulus in articular cartilage [6,23]. Recent studies have shown that chondrocyte apoptosis induced by shear forces and/or hydrostatic pressure is mediated in part by increased NO production [26,30]. Other reactive oxygen species such as hydrogen peroxide also induce apoptosis in cultured chondrocytes [3,32].…”

“…Although a variety of different stimuli initiate chondrocyte apoptosis [2,3,6,9,10,23,24,26,30,32], a universal feature of chondrocyte apoptosis is caspase activation [13,16,17,31,35,39,44] (Fig. 1).…”