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MRNA levels were evaluated by real time RT-PCR. A schematic representation of the AR-mTOR cross-talk in a high and low testosterone conditions. Disrupting this loop during the window of maximal cell stress immediately after initiation of ADT may block the progression of androgen-dependent prostate cancer to ADT-resistant prostate cancer. At the very least, mTOR is restored to a ‘survival threshold’ so that it is in a position to keep protein synthesis to a minimum.In contrast to testosterone, DHT did not prevent the induction of AR by rapamycin (Figure 4C). Another experiment was carried out to determine whether dihydrotestosterone (DHT) has the same effect on rapamycin induction of AR as testosterone. The increase of PSA and KLK2 at 0.03 and 1 nM testosterone paralleled the increase of AR expression. The data suggest that AR expression is up-regulated when mTOR is depressed, but this loop was operative only in a low testosterone condition. However, at 5 nM testosterone, the induction of AR by rapamycin was no longer evident. Up to this point, the results indicated that AR positively regulates mTOR activity in both low and high testosterone conditions.
There was no difference in the levels of IVST and LVPWT between low-dose and medium-dose groups. The high-dose rapamycin group showed significant reductions in the HW/TL level, whereas the low-dose and medium-dose rapamycin groups had no significant effect on the HW/TL level. After the intervention of different doses of rapamycin, the blood pressure measurement values of rats at various time points had statistical difference, and the effect of rapamycin on blood pressure remained stable (Fig. 1C and D).
As expected, the expression of AR targets, such as PSA and KLK2, decreased significantly. AR was knocked down successfully by siRNA in both testosterone conditions (Figure 2A). Total protein level of the unphosphorylated substrates was not affected by bicalutamide.
MTOR, ribosomal protein S6 kinase (S6K1), 4E-binding protein 1 (4EBP1) and eukaryotic translation initiation factor 4E in myocardial tissue of OVX + estrogen + testosterone group were expressed at higher levels than those of the other four groups. Multiple factors and pathways affect mTORC1 activity to regulate skeletal muscle mass. mTORC1 is activated by IGF-I/insulin, mechanical stimulation and amino acids (blue lines) and inhibited by glucocorticoids and myostatin (red lines). Hence, dissection of mTOR signaling provides useful potential therapeutic strategies in boosting skeletal muscle growth and preventing muscle loss. While mTOR has been appreciated as a main regulator of protein synthesis in skeletal muscle, its crosstalk with muscle atrophy inducing triggers, such as myostatin and glucocorticoids, have been studied. Indeed, the expression of myostatin mRNA and protein are increased in a dose-dependent manner in dexamethasone-treated rats (Ma et al., 2003).
Rapamycin eliminated the effect of T on myocardial area (original magnification ×400). Testosterone aggrandized the expression level… Testosterone induces OVX SHR myocardial… MTOR inhibitor rapamycin abolished the… Our team's previous research identified that androgen was an underlying factor contributing to increased blood pressure and LVH in postmenopausal women. A schematic representation of the AR-mTOR cross-talk in a high and low testosterone… Effect of AR siRNA knockdown on mTOR activity.
Chronic mTORC1 activation through TSC1 knockout in old muscle leads to muscle atrophy mainly due to inability to induce autophagy (Castets et al., 2013), suggesting the importance of mTOR-induced regulation of autophagy in aged muscle. Nevertheless, the hyperactivation of mTOR in aged muscles does not induce protein synthesis (Markofski et al., 2015). Inhibition of mTOR signaling in aged muscle may have similar beneficial effects on multiple age related pathologies (Johnson et al., 2013b). Of note, the hyperphosphorylation of mTORC1 was observed in aged human muscles (Sandri et al., 2013; Markofski et al., 2015). The amount of circulatory IGF-I and IGF-I mRNA levels are reduced (Leger et al., 2008), and subsequently the activity of Akt/mTOR/p70S6K1 are decreased in older age groups compared to one in younger groups (Pallafacchina et al., 2002; Cuthbertson et al., 2005; Leger et al., 2008). It is characterized by overall decreases in size and number of skeletal muscle fibers, mostly the type 2 or fast-twitch muscle fibers, and a marked infiltration of fibrous and adipose tissue into the skeletal muscle (Walston, 2012). The overexpression of myostatin decreases Akt and mTORC1 components, such as p70S6K1, S6, and 4EBP1 (Amirouche et al., 2009).
However, the testosterone sensitivity of Akt/mTOR signaling requires further understanding in order to grasp the significance of varied testosterone levels seen with wasting disease on muscle protein turnover regulation. The outcome is predictable because the low testosterone-acclimated cells are able to up-regulate AR protein and activity, and are therefore better equipped for survival in a stress situation. The data of the scrambled siRNA control cells presented in Figure 2B show that the phosphorylation of p70S6K and S6 was increased by testosterone stimulation (lane 1 vs. lane 3). These results indicated that the mTOR pathway plays a key role in testosterone-induced OVX SHR myocardial hypertrophy. Finally, the relationship between the total elevated levels of these proteins (mTOR, S6K1 and 4E-BP1) induced by testosterone and their phosphorylated form remains unclear and requires further investigation. First, this study effectively identified the mTOR signaling pathway as a potential target of testosterone-induced OVX SHR cardiac hypertrophy, but it did not explore mTOR upstream regulatory molecules.