Andrea Vasconsuelo

Role of 17β-estradiol and testosterone in apoptosis.

17β-Estradiol (E2) and Testosterone (T) exert actions in most animal tissues, in addition to the reproductive system. Thus, both sex steroid hormones affect growth and different cell functions in several organs. Accordingly, the nuclear estrogen (ER) and androgen (AR) receptors are ubiquitously expressed. Moreover, ER and AR may have non-classical intracellular localizations, e.g. plasma membrane, mitochondria and endoplasmic reticulum, raising additional complexity to the functional roles of E2 and T. In addition to the modulation of gene transcription by direct interaction with their cognate nuclear receptors, the steroids can rapidly activate signaling pathways by a non-genomic mechanism mediated by receptors identical to or different from known steroid receptors. Among various functions, E2 and T can regulate apoptosis through those pathways. In mitochondria, the presence of ER and AR and actions of estrogen and androgen have been shown, in keeping with the organelle being a control point of apoptosis. The most recurrent action for each steroid hormone is the protection of mitochondria against different insults, resulting in antiapoptosis. This review summarizes the molecular basis of the modulation of programmed cell death by E2 and T in several tissues.

17β-Estradiol signaling in skeletal muscle cells and its relationship to apoptosis

17beta-estradiol exerts an antiapoptotic action in skeletal muscle cells through extranuclear ERalpha and beta. This protective action, mainly involves a non-genomic mechanism of ERK1/2 and PI3K/Akt activation and BAD phosphorylation. ERbeta plays a major role in the inhibition of apoptosis by 17beta-estradiol at the level of mitochondria, whereas ERalpha and ERbeta mediate the activation of Akt to the same extent, suggesting differential involvement of ER isoforms depending on the step of the apoptotic/survival pathway involved. The myopathies associated to estrogen deficit states may be related to the mechanisms by which estrogen regulates apoptosis.

Expression and subcellular distribution of native estrogen receptor β in murine C2C12 cells and skeletal muscle tissue

We have recently described the expression and intracellular localization of ER alpha in murine C2C12 cells and skeletal muscle tissue. In separate studies, a protective role of 17beta-estradiol against apoptosis exerted mainly at the mitochondrial level was also shown in the C2C12 muscle cell line. However, this functional evidence was in accordance with the participation of ER beta. We have then here investigated the expression and subcellular distribution of native ER beta in similar skeletal muscle cultured cells and tissue developed in vivo. ER beta was detected by immunoblotting using specific antibodies and ligand blot analysis after subcellular fractionation. Immunolocalization was confirmed using conventional and confocal microscopy. ER beta was found to a great extent in mitochondria and in lower amounts in the cytosolic fraction, differently to ER alpha which localizes in microsomes, cytosol, mitochondria, and also in the nucleus of muscle tissue. ER beta expression was also demonstrated by RT-PCR. Finally, the mitochondrial localization of native ER beta in C2C12 muscle cells was corroborated after transient transfection with specific ER beta siRNAs. These data raise the possibility that the antiapoptotic action of 17beta-estradiol in muscle cells may be related in part to a direct action of the hormone on mitochondria through ER beta.

Participation of HSP27 in the antiapoptotic action of 17β-estradiol in skeletal muscle cells

Exposure to 17β-estradiol prior to induction of apoptosis protects skeletal muscle cells against damage. The mechanism involved in this protective action of the hormone is poorly understood. In the present study, using the murine muscle cell line C2C12, evidence was obtained that inhibition of H2O2-induced apoptosis by the estrogen requires the participation of heat shock protein 27 (HSP27). Reverse transcriptase polymerase chain reaction, Western blot, and immunocytochemistry assays showed that 17β-estradiol induces a time-dependent (5–60xa0min) increase in the expression of HSP27. In addition, in presence of quercetin, an inhibitor of HSPs, the antiapoptotic effect of the hormone was diminished. More specifically, blockage experiments with short interference RNA targeting HSP27 confirmed the role of this chaperone in the protective effect of the steroid. 17β-Estradiol abolished caspase-3 cleavage elicited by H2O2. Coimmunoprecipitation assays suggested physical interaction of HSP27 with caspase-3 in presence of estradiol. Furthermore, we observed that this chaperone interacts with estrogen receptors (ER) β in mitochondria. Then, this study suggests that HSP27 plays a new role in the antiapoptotic action triggered by 17β-estradiol by modulating caspase-3 activity and stabilizing ERβ in skeletal muscle cells.

Actions of 17β-estradiol and testosterone in the mitochondria and their implications in aging.

A decline in the mitochondrial functions and aging are two closely related processes. The presence of estrogen and androgen receptors and hormone-responsive elements in the mitochondria represents the starting point for the investigation of the effects of 17β-estradiol and testosterone on the mitochondrial functions and their relationships with aging. Both steroids trigger a complex molecular mechanism that involves crosstalk between the mitochondria, nucleus, and plasma membrane, and the cytoskeleton plays a key role in these interactions. The result of this signaling is mitochondrial protection. Therefore, the molecular components of the pathways activated by the sexual steroids could represent targets for anti-aging therapies. In this review, we discuss previous studies that describe the estrogen- and testosterone-dependent actions on the mitochondrial processes implicated in aging.

Estradiol exerts antiapoptotic effects in skeletal myoblasts via mitochondrial PTP and MnSOD

17β-Estradiol (E(2)) protects several non-reproductive tissues from apoptosis, including skeletal muscle. We have shown that E(2) at physiological concentrations prevented apoptosis induced by H(2)O(2) in C2C12 skeletal myoblasts. As we also demonstrated the presence of estrogen receptors in mitochondria, the present work was focused on the effects of E(2) on this organelle. Specifically, we evaluated the actions of E(2) on the mitochondrial permeability transition pore (MPTP) by the calcein-acetoxymethylester/cobalt method using fluorescence microscopy and flow cytometry. Pretreatment with E(2) prevented MPTP opening induced by H(2)O(2), which preceded loss of mitochondrial membrane potential. In addition, it was observed that H(2)O(2) induced translocation of Bax to mitochondria; however, in the presence of the steroid this effect was abrogated suggesting that members of the Bcl-2 family may be regulated by E(2) to exert an antiapoptotic effect. Moreover, E(2) increased mitochondrial manganese superoxide dismutase protein expression and activity, as part of a mechanism activated by E(2) that improved mitochondrial performance. Our results suggest a role of E(2) in the regulation of apoptosis with a clear action at the mitochondrial level in C2C12 skeletal myoblast cells.

Effects of Photobiomodulation Therapy on Oxidative Stress in Muscle Injury Animal Models: A Systematic Review

This systematic review was performed to identify the role of photobiomodulation therapy on experimental muscle injury models linked to induce oxidative stress. EMBASE, PubMed, and CINAHL were searched for studies published from January 2006 to January 2016 in the areas of laser and oxidative stress. Any animal model using photobiomodulation therapy to modulate oxidative stress was included in analysis. Eight studies were selected from 68 original articles targeted on laser irradiation and oxidative stress. Articles were critically assessed by two independent raters with a structured tool for rating the research quality. Although the small number of studies limits conclusions, the current literature indicates that photobiomodulation therapy can be an effective short-term approach to reduce oxidative stress markers (e.g., thiobarbituric acid-reactive) and to increase antioxidant substances (e.g., catalase, glutathione peroxidase, and superoxide dismutase). However, there is a nonuniformity in the terminology used to describe the parameters and dose for low-level laser treatment.