Estrogen inhibits starvation‐induced apoptosis in osteocytes by a redox‐independent process involving association of JNK and glutathione S‐transferase P1‐1

Abstract

Estrogen deficiency causes bone loss as a result of microdamage, oxidative stress, and osteocyte apoptosis. A relationship between oxidative stress‐induced apoptosis, c‐Jun N‐terminal kinase (JNK) activation, and expression of factors involved in bone remodeling has been demonstrated in osteocytes. However, the molecular regulation of these events in osteocytes treated with 17β‐estradiol (17β‐E2) remains unexplored. The MLO‐Y4 murine osteocyte‐like cell line was used as a model to study starvation‐induced apoptosis and ROS production during 17β‐E2 treatment. Expression of glutathione S‐transferase P1‐1 (GSTP1‐1), receptor activator kB ligand (RANKL), osteoprotegerin (OPG), sclerostin, and kinases activation were measured by western blot. In addition, the GSTP1‐1/JNK association was assessed by immunoprecipitation, and GSTP1‐1 involvement in the osteocyte response to 17β‐E2 was detected by specific siRNA transfection. 17β‐E2 prevents starvation‐induced apoptosis (DNA fragmentation and caspase activation), the increase in sclerostin expression and the RANKL/OPG ratio, which are all related to JNK activation due to oxidative stress in osteocytes. This occurs through GSTP1‐1 overexpression, which can inhibit JNK activation by formation of a GSTP1‐1/JNK complex. No early antioxidant action of 17β‐E2 has been found but the estrogen effect is similar to N‐acetylcysteine which, by increasing the intracellular redox state, maintains JNK bound to GSTP1‐1. Thus, the antiapoptotic and osteogenic effect of 17β‐E2 in MLO‐Y4 occurs by a redox‐independent process involving GSTP1‐1/JNK association. This study clarifies at molecular level the effect of 17β‐E2 on osteocyte activity and identifies a possible role of GSTP1‐1 and JNK activity in bone remodeling and repair mechanisms.

Blueberry juice protects osteocytes and bone precursor cells against oxidative stress partly through SIRT1

“…*P ≤ 0.001 compared to BJand BE-treated cells without EX527 or with Scr siRNA; ○ P ≤ 0.01 compared to the respective untreated starved cells with EX527 or with SIRT1 siRNA; Δ P ≤ 0.001 compared to untreated starved cells. similar to what occurs in vivo in the bone environment after microdamage and oestrogen deficiency [12,14,18,26,47]. Previously, it has been demonstrated that oxidative stress-induced apoptosis by starvation in MLO-Y4 cells is involved in the up-regulation of osteoclastogenic factors [18].…”

“…Moreover, polyphenol-derived phenolic acid present in serum from BB diet-fed rats is bioactive, stimulating osteoblast differentiation and bone mineralization through Wnt signalling [2,23]. Previous data demonstrated that in MLO-Y4 cells, starvation-induced apoptosis is closely related to increased mitochondrial ROS production, which, through JNK activity, induces caspase-3 activation [18,47]. Furthermore, this study demonstrates that the antiapoptotic ability (apoptosis reduction of about 70-80%) of BJ and BE is higher than their antioxidant capacity (ROS reduction of about 50%).…”

Vitamin D Replacement Mitigates Menopause-Associated Dyslipidaemia and Atherogenic Indices in Ovariectomized Rats; A Biochemical Study

“…Our results revealed an observed increase in the aortic JNK activity in the OVX and VD-sufficient group compared to the SHAM. This could be explained by withdrawal of estrogen's JNKsuppressor effect [46] and menopause-associated oxidative stress, dyslipidaemia, and inflammatory cytokines that are known stressors activating JNK [42].…”

Stra8 may inhibit apoptosis during mouse spermatogenesis via the AKT signaling pathway

“…GSTP1, a dimeric protein, binds to JNK and suppresses downstream JNK g signaling (36). To the best of our knowledge, the JNK signaling pathway is involved in the processes of cell death and mediates stress-induced apoptosis via mitochondrial pathways with the release of cytochrome c-activating caspases (CASP3, -6, and -7) (36,37). Therefore, the present study detected the expression of P38, ERK, USP33, TCF4 and GSTP1.…”

“…The phosphorylation of TCF4 at the serine/threonine proceeds via ERK and p-38 dependent pathways, and TcF4 knockdown has been shown to induce growth arrest and apoptosis in human colorectal cancer (34,35). GSTP1, a dimeric protein, binds to JNK and suppresses downstream JNK g signaling (36). To the best of our knowledge, the JNK signaling pathway is involved in the processes of cell death and mediates stress-induced apoptosis via mitochondrial pathways with the release of cytochrome c-activating caspases (CASP3, -6, and -7) (36,37).…”