Loss of ovarian function in mice results in abrogated skeletal muscle PPARdelta and FoxO1-mediated gene expression

GPER activation attenuates cardiac dysfunction by upregulating the SIRT1/3-AMPK-UCP2 pathway in postmenopausal diabetic rats

Postmenopausal diabetic women are at higher risk to develop cardiovascular diseases (CVD) compared with nondiabetic women. Alterations in cardiac cellular metabolism caused by changes in sirtuins are one of the main causes of CVD in postmenopausal diabetic women. Several studies have demonstrated the beneficial actions of the G protein-coupled estrogen receptor (GPER) in postmenopausal diabetic CVD. However, the molecular mechanisms by which GPER has a cardioprotective effect are still not well understood. In this study, we used an ovariectomized (OVX) type-two diabetic (T2D) rat model induced by high-fat diet/streptozotocin to investigate the effect of G-1 (GPER-agonist) on sirtuins, and their downstream pathways involved in regulation of cardiac metabolism and function. Animals were divided into five groups: Sham-Control, T2D, OVX+T2D, OVX+T2D+Vehicle, and OVX+T2D+G-1. G-1 was administrated for six weeks. At the end, hemodynamic factors were measured, and protein levels of sirtuins, AMP-activated protein kinase (AMPK), and uncoupling protein 2 (UCP2) were determined by Western blot analysis. In addition, cardiac levels of oxidative stress biomarkers were measured. The findings showed that T2D led to left ventricular dysfunction and signs of oxidative stress in the myocardium, which were accompanied by decreased protein levels of Sirt1/2/3/6, p-AMPK, and UCP2 in the heart. Moreover, the induction of the menopausal state exacerbated these changes. In contrast, treatment with G-1 ameliorated the hemodynamic changes associated with ovariectomy by increasing Sirt1/3, p-AMPK, UCP2, and improving oxidative status. The results provide evidence of the cardioprotective effects of GPER operating through Sirt1/3, p-AMPK, and UCP2, thereby improving cardiac function. Our results suggest that increasing Sirt1/3 levels may offer new therapeutic approaches for postmenopausal diabetic CVD.

An integrated study of hormone-related sarcopenia for modeling and comparative transcriptome in rats

Sarcopenia is a senile disease with high morbidity, serious complications and limited clinical treatments. Menopause increases the risk of sarcopenia in females, while the exact pathogenesis remains unclear. To systematically investigate the development of hormone-related sarcopenia, we established a model of sarcopenia by ovariectomy and recorded successive characteristic changes. Furthermore, we performed the transcriptome RNA sequencing and bioinformatics analysis on this model to explore the underlying mechanism. In our study, we identified an integrated model combining obesity, osteoporosis and sarcopenia. Functional enrichment analyses showed that most of the significantly enriched pathways were down-regulated and closely correlated with endocrine and metabolism, muscle dysfunction, cognitive impairment and multiple important signaling pathways. We finally selected eight candidate genes to verify their expression levels. These findings confirmed the importance of estrogen in the maintenance of skeletal muscle function and homeostasis, and provided potential targets for further study on hormone-related sarcopenia.

Aging is associated with loss of beneficial effects of estrogen on leptin responsiveness in mice fed high fat diet: Role of estrogen receptor α and cytokines

Aging causes changes in body composition and energy balance. Estrogen plays an important role in body's metabolism. The aim of this study was to determine whether estrogen has beneficial effects on leptin responsiveness in aged mice. Young 4 months and aged 19-21 female mice fed High Fat Diet (HFD) or Standard Diet (SD) for 12 weeks and following received estrogen for 4 weeks. Responsiveness to leptin was compared by measuring energy balance parameters. Results showed that HFD caused weight gain compared to SD in young, but had no effect on aged animals. Estrogen reduced body weight, energy intake and visceral fat in young, while none of these parameters was affected in aged animals. Although there was leptin sensitivity in aged compared to ovariectomized animals, estrogen only improved the sensitivity of young to leptin. Estrogen prevented increase in TNF-α and a decrease in IL-10 in HFD young and aged animals. Response to estrogen depended on age, and estrogen increased leptin sensitivity only in young animals. Determining the exact mechanism of this action is suggested in future studies.

The PPARδ Agonist GW501516 Improves Lipolytic/Lipogenic Balance through CPT1 and PEPCK during the Development of Pre-Implantation Bovine Embryos

The PPARs (peroxisome proliferator-activated receptors) play critical roles in the regulation of lipid and glucose metabolism. PPARδ, a member of the PPARs family, is associated with decreased susceptibility to ectopic lipid deposition and is implicated in the regulation of mitochondrial processes. The current study aimed to determine the role of PPARδ in fatty acid β-oxidation and its influence on PEPCK for the lipogenic/lipolytic balance during in vitro bovine oocyte maturation and embryo development. Activation of PPARδ by GW501516, but not 2-BP, was indicated by intact embryonic PEPCK (cytosolic) and CPT1 expression and the balance between free fatty acids and mitochondrial β-oxidation that reduced ROS and inhibited p-NF-κB nuclear localization. Genes involved in lipolysis, fatty acid oxidation, and apoptosis showed significant differences after the GW501516 treatment relative to the control- and 2-BP-treated embryos. GSK3787 reversed the PPARδ-induced effects by reducing PEPCK and CPT1 expression and the mitochondrial membrane potential, revealing the importance of PPARδ/PEPCK and PPARδ/CPT1 for controlling lipolysis during embryo development. In conclusion, GW501516-activated PPARδ maintained the correlation between lipolysis and lipogenesis by enhancing PEPCK and CPT1 to improve bovine embryo quality.

Aging of the musculoskeletal system: How the loss of estrogen impacts muscle strength

Skeletal muscle weakness occurs with aging and in females this is compounded by the loss of estrogen with ovarian failure. Estrogen deficiency mediates decrements in muscle strength from both inadequate preservation of skeletal muscle mass and decrements in the quality of the remaining skeletal muscle. Processes and components of skeletal muscle that are affected by estrogens are beginning to be identified. This review focuses on mechanisms that contribute to the loss of muscle force generation when estrogen is low in females, and conversely the maintenance of strength by estrogen. Evidence is accumulating that estrogen deficiency induces apoptosis in skeletal muscle contributing to loss of mass and thus strength. Estrogen sensitive processes that affect quality, i.e., force generating capacity of muscle, include myosin phosphorylation and satellite cell function. Further detailing these mechanisms and identifying additional mechanisms that underlie estrogenic effects on skeletal muscle is important foundation for the design of therapeutic strategies to minimize skeletal muscle pathologies, such as sarcopenia and dynapenia.

Combinatory effects of phytoestrogens and exercise on body fat mass and lipid metabolism in ovariectomized female rats

The purpose of this study was to investigate the combinatory effects of an isoflavone (ISO)-rich diet and exercise on fat mass and lipid metabolism in ovariectomized (OVX) rats. Therefore the female Wistar rats were sedentary, performed an intense treadmill uphill running, received ISOs, or a combination of ISOs and running after ovariectomy. The exercise reduced visceral fat mass, adipocyte size and serum leptin in Sham animals and antagonized the increases of these parameters induced by OVX. ISOs reduced OVX induced increase of serum leptin. The combination of training and ISOs was most effective in reducing serum triglyceride levels. In OVX rats the training stimulated the expression of genes associated with fatty acid synthesis (SREBP-1c and FAS) in adipose tissue, soleus muscle, liver and genes associated with fatty acid oxidation (PPARδ and PGC-1α) in adipose tissue. ISOs stimulated the expression of SREBP-1c and FAS in soleus muscle and PGC-1α in adipose tissue, whereas suppressed hepatic SREBP-1c and FAS expression. Strong additive effects of ISOs combined with the training were observed for PPARδ and PGC-1α expressions in soleus muscle. In conclusion our results demonstrate that both the training and ISOs affect fat mass and fatty acid metabolism in OVX rats. The training seems to have a higher impact than ISO exposure in regulating gene expression in adipose tissue. However, the strongest effects for several of the addressed parameters could be observed in the combination group especially in the soleus muscle. Therefore a combination of training and an ISO-rich diet may have beneficial effects on fatty acid metabolism and could be a concept for the prevention of obesity in postmenopausal females.

Estradiol modulates myosin regulatory light chain phosphorylation and contractility in skeletal muscle of female mice

Impairment of skeletal muscle function has been associated with changes in ovarian hormones, especially estradiol. To elucidate mechanisms of estradiol on skeletal muscle strength, the hormone's effects on phosphorylation of the myosin regulatory light chain (pRLC) and muscle contractility were investigated, hypothesizing an estradiol-specific beneficial impact. In a skeletal muscle cell line, C2C12, pRLC was increased by 17β-estradiol (E2) in a concentration-dependent manner. In skeletal muscles of C57BL/6 mice that were E2 deficient via ovariectomy (OVX), pRLC was lower than that from ovary-intact, sham-operated mice (Sham). The reduced pRLC in OVX muscle was reversed by in vivo E2 treatment. Posttetanic potentiation (PTP) of muscle from OVX mice was low compared with that from Sham mice, and this decrement was reversed by acute E2 treatment, demonstrating physiological consequence. Western blot of those muscles revealed that low PTP corresponded with low pRLC and higher PTP with greater pRLC. We aimed to elucidate signaling pathways affecting E2-mediated pRLC using a kinase inhibitor library and C2C12 cells as well as a specific myosin light chain kinase inhibitor in muscles. PI3K/Akt, MAPK, and CamKII were identified as candidate kinases sensitive to E2 in terms of phosphorylating RLC. Applying siRNA strategy in C2C12 cells, pRLC triggered by E2 was found to be mediated by estrogen receptor-β and the G protein-coupled estrogen receptor. Together, these results provide evidence that E2 modulates myosin pRLC in skeletal muscle and is one mechanism by which this hormone can affect muscle contractility in females.

The emerging role of skeletal muscle oxidative metabolism as a biological target and cellular regulator of cancer-induced muscle wasting

While skeletal muscle mass is an established primary outcome related to understanding cancer cachexia mechanisms, considerable gaps exist in our understanding of muscle biochemical and functional properties that have recognized roles in systemic health. Skeletal muscle quality is a classification beyond mass, and is aligned with muscle's metabolic capacity and substrate utilization flexibility. This supplies an additional role for the mitochondria in cancer-induced muscle wasting. While the historical assessment of mitochondria content and function during cancer-induced muscle loss was closely aligned with energy flux and wasting susceptibility, this understanding has expanded to link mitochondria dysfunction to cellular processes regulating myofiber wasting. The primary objective of this article is to highlight muscle mitochondria and oxidative metabolism as a biological target of cancer cachexia and also as a cellular regulator of cancer-induced muscle wasting. Initially, we examine the role of muscle metabolic phenotype and mitochondria content in cancer-induced wasting susceptibility. We then assess the evidence for cancer-induced regulation of skeletal muscle mitochondrial biogenesis, dynamics, mitophagy, and oxidative stress. In addition, we discuss environments associated with cancer cachexia that can impact the regulation of skeletal muscle oxidative metabolism. The article also examines the role of cytokine-mediated regulation of mitochondria function, followed by the potential role of cancer-induced hypogonadism. Lastly, a role for decreased muscle use in cancer-induced mitochondrial dysfunction is reviewed.

Effects of sex steroids on bones and muscles: Similarities, parallels, and putative interactions in health and disease

Estrogens and androgens influence the growth and maintenance of bones and muscles and are responsible for their sexual dimorphism. A decline in their circulating levels leads to loss of mass and functional integrity in both tissues. In the article, we highlight the similarities of the molecular and cellular mechanisms of action of sex steroids in the two tissues; the commonality of a critical role of mechanical forces on tissue mass and function; emerging evidence for an interplay between mechanical forces and hormonal and growth factor signals in both bones and muscles; as well as the current state of evidence for or against a cross-talk between muscles and bone. In addition, we review evidence for the parallels in the development of osteoporosis and sarcopenia with advancing age and the potential common mechanisms responsible for the age-dependent involution of these two tissues. Lastly, we discuss the striking difference in the availability of several drug therapies for the prevention and treatment of osteoporosis, as compared to none for sarcopenia. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Diminished satellite cells and elevated adipogenic gene expression in muscle as caused by ovariectomy are averted by low-magnitude mechanical signals

Age-related degeneration of the musculoskeletal system, accelerated by menopause, is further complicated by increased systemic and muscular adiposity. The purpose of this study was to identify at the molecular, cellular, and tissue levels the impact of ovariectomy on adiposity and satellite cell populations in mice and whether mechanical signals could influence any outcomes. Eight-week-old C57BL/6 mice were ovariectomized, with one half subjected to low-intensity vibration (LIV; 0.3 g/90 Hz, 15 min/day, 5 day/wk; n = 10) for 6 wk and the others sham vibrated (OVX; n = 10). Data are compared with age-matched, intact controls (AC; n = 10). In vivo μCT analysis showed that OVX mice gained 43% total (P < 0.001) and 125% visceral adiposity (P < 0.001) compared with their baseline after 6 wk, whereas LIV gained only 21% total (P = 0.01) and 70% visceral adiposity (P < 0.01). Relative to AC, expression of adipogenic genes (PPARγ, FABP4, PPARδ, and FoxO1) was upregulated in OVX muscle (P < 0.05), whereas LIV reduced these levels (P < 0.05). Adipogenic gene expression was inversely related to the percentage of total and reserve satellite cell populations in the muscle, with both declining in OVX compared with AC (-21 and -28%, respectively, P < 0.01). LIV mitigated these declines (-11 and -17%, respectively). These results provide further evidence of the negative consequences of estrogen depletion and demonstrate that mechanical signals have the potential to interrupt subsequent adipogenic gene expression and satellite cell suppression, emphasizing the importance of physical signals in protecting musculoskeletal integrity and slowing the fat phenotype.

Microarray gene expression profiling and bioinformatics analysis of premature ovarian failure in a rat model

Premature ovarian failure (POF) remains one of the major gynecological problems worldwide which affected 1% of women. Even though tremendous achievements had been acquired as opposed to years past, molecular pathogenesis associated with POF is still unclear and needs to be well-defined. The aim of this study was to analyze the gene expression profiles in the POF rat model. To predict potential regulating factors, we firstly treated female Sprague Dawley (SD) rat with 4-vinylcyclohexene diepoxide (VCD). Total RNA from ovarian tissue was converted to cDNA and hybridized to mRNA Chip array. The differentially expressed genes (DEGs) were identified by two-sample t test and assessed using hierarchical clustering and Principal Component Analysis methods. Potential regulatory targets associated with these DEGs were constructed using BisoGenet in Cytoscape. Gene Ontology (GO) and functional enrichment analysis were performed using BiNGO and DAVID, respectively. As the results, 25 DEGs were found to be closely associated with POF initiation. Hierarchical clustering and Principal Component Analysis on the transcriptional profiles revealed an excellent separation of the vehicle and POF compartments. Pathway enrichment analysis based on the disease-gene interaction network analysis led to the identification of two core signaling pathways that were strongly affected during POF initiation and progression: immune response and cardiovascular disorders. In conclusion, we constructed a gene regulatory network associated with POF using the microarray gene expression profiling, and screened out some genes or transcription factors that may be used as potential molecular therapeutic targets for POF.

Elite athletes live longer than the general population: a meta-analysis

OBJECTIVE

To perform a meta-analysis of cohort studies aimed at providing an accurate overview of mortality in elite athletes.

PATIENTS AND METHODS

We reviewed English-language scientific articles available in Medline and Web of Science databases following the recommendations of the Meta-analyses Of Observational Studies in Epidemiology group. We searched for publications on longevity and professional or elite athletes (with no restriction on the starting date and up to March 31, 2014).

RESULTS

Ten studies, including data from a total of 42,807 athletes (707 women), met all inclusion criteria. The all-cause pooled standard mortality ratio (SMR) was 0.67 (95% CI, 0.55-0.81; P<.001) with no evidence of publication bias (P=.24) but with significant heterogeneity among studies (I(2)=96%; Q=224.46; P<.001). Six studies provided data on cardiovascular disease (CVD) and 5 on cancer (in a total of 35,920 and 12,119 athletes, respectively). When only CVD was considered as a cause of mortality, the pooled SMR was 0.73 (95% CI, 0.65-0.82; P<.001) with no evidence of bias (P=.68) or heterogenity among studies (I(2)=38%; Q=8.07; P=.15). The SMR for cancer was 0.60 (95% CI, 0.38-0.94; P=.03) with no evidence of bias (P=.20) despite a significant heterogeneity (I(2)=91%; Q=44.21; P<.001).

CONCLUSION

The evidence available indicates that top-level athletes live longer than the general population and have a lower risk of 2 major causes of mortality, namely, CVD and cancer.

Effects of the peroxisome proliferator-activated receptor (PPAR)-δ agonist GW501516 on bone and muscle in ovariectomized rats

Estrogen deficiency promotes bone loss and skeletal muscle dysfunction. Peroxisome proliferator-activated receptors (PPARs) have 3 subtypes (α, δ, and γ). PPARγ agonists induce bone loss, whereas PPARα agonists increase bone mass. Although PPARδ agonists are known to influence skeletal muscle metabolism, the skeletal effects are unsettled. This study investigated the musculoskeletal effects of the PPARδ agonist GW501516 in ovariectomized (OVX) rats. Female Sprague Dawley rats, 12 weeks of age, were allocated to a sham-operated group and 3 OVX groups; high-dose GW501516 (OVX-GW5), low-dose GW501516 (OVX-GW1), and a control group (OVX-CTR), respectively (n = 12 per group). Animals received GW501516 or vehicle (methylcellulose) daily for 4 months by gavage. Bone mineral density (BMD) was assessed by dual x-ray absorptiometry at the femur, spine, and whole body. Bone microarchitecture at the proximal tibia was assessed by microcomputed tomography, and dynamic histomorphometry was performed. Quadriceps muscle morphology and the relative expression of mitochondrial proteins were analyzed. Bone metabolism markers and metabolic markers were measured in plasma. After 4 months, the OVX-GW5 group displayed lower femoral BMD than OVX-CTR. Trabecular separation was higher in the GW-treated groups, compared with OVX-CTR. The OVX-GW5 group also exhibited lower cortical area fraction and a higher structure model index than OVX-CTR. These effects coincided with impaired bone formation in both GW groups. The OVX-GW5 group displayed elevated triglyceride levels and reduced adiponectin levels, whereas no effects on muscle morphology or mitochondrial gene expression appeared. In summary, the PPARδ agonist GW501516 negatively affected bone properties in OVX rats, whereas no effects were detected in skeletal muscle.

Sex, fiber-type, and age dependent in vitro proliferation of mouse muscle satellite cells

During postnatal growth and after muscle injury, satellite cells proliferate and differentiate into myotubes to form and repair musculature. Comparison of studies on satellite cell proliferation and differentiation characteristics is confounded by the heterogeneity of the experimental conditions used. To examine the influence of sex, age, and fiber-type origin on in vitro properties of satellite cells derived from postnatal muscles, fast extensor digitorum longus (EDL) and slow soleus (SOL) muscles were extracted from male and female mice of 1 week to 3 months of age. Myoblast proliferation and myogenic regulatory factor (MRF) expression was measured from cultures of freshly isolated satellite cells. Higher proliferation rate and elevated Myod1 expression was found in male EDL and SOL derived cells compared with females at age of 40, 60, and 120 days, whereas inverse tendency for cell proliferation was apparent in EDL of juvenile (7-day-old) pups. Myogenin and Mrf4 transcripts were generally elevated in males of 40 and 60 days of age and in female EDL of juveniles. However, these differentiation markers did not significantly correlate with proliferation rate at all ages. Pax7, whose overexpression can block myogenesis, was up-regulated especially in 40-day-old females where MRF expression was low. These results indicate that gender, postnatal age, and muscle fiber origin affect proliferation and muscle transcription factor expression in vitro. The results also support the view that satellite cells originating from slow and fast muscles are intrinsically different and warrant further studies on the effect of cell origin for therapeutic approaches.

Effects of high-fat diet on plasma lipids, adiposity, and inflammatory markers in ovariectomized C57BL/6 mice

OBJECTIVE

We hypothesized that a high-fat (HF) diet aggravates ovariectomy-related complications. To test this hypothesis, ovariectomized (OVX) mice were fed a HF diet, and we investigated the lipid metabolism, adipose tissue remodeling, adipokines, and inflammatory cytokines.

METHODS

To investigate the situation in a mouse model of ovariectomy, OVX and SHAM C57BL/6 mice fed a HF diet (60% fat) or standard chow (SC, 10% fat) were monitored for 18 wk. We evaluated daily food intake and weekly body weight. Mice were killed at 30 wk of age. Blood samples and adipose tissue were collected for biochemical, histologic, and molecular analysis.

RESULTS

OVX groups showed atrophied uterus compared to the SHAM groups, ensuring the success of surgically induced menopause. Despite lower food intake, OVX-HF mice gained about 52% more weight and had heavier total body fats, especially in relation to ovarian fat pad (372%)-a visceral fat which is associated with increased pathogenicity in obesity, and showed larger adipocytes (30%) when compared to OVX-SC mice. Biochemical analysis showed that the OVX-HF mice had increased levels of serum total cholesterol (51%), greater serum triglycerides (158%), lower serum adiponectin (40%), and higher plasma leptin (323%) than OVX-SC mice. The obese group (OVX-HF) also had higher IL-6 levels than both SHAM-HF (241%) and OVX-SC mice (870%).

CONCLUSION

OVX C57BL/6 mice fed HF diet had greater adipose fat pad, larger adipocytes, and increased inflammatory markers, reinforcing the idea that a HF diet aggravates the complications of ovariectomy-associated inflammation.

Estrogen regulates estrogen receptors and antioxidant gene expression in mouse skeletal muscle

BACKGROUND

Estrogens are associated with the loss of skeletal muscle strength in women with age. Ovarian hormone removal by ovariectomy in mice leads to a loss of muscle strength, which is reversed with 17beta-estradiol replacement. Aging is also associated with an increase in antioxidant stress, and estrogens can improve antioxidant status via their interaction with estrogen receptors (ER) to regulate antioxidant gene expression. The purpose of this study was to determine if ER and antioxidant gene expression in skeletal muscle are responsive to changes in circulating estradiol, and if ERs regulate antioxidant gene expression in this tissue.

METHODOLOGY/PRINCIPAL FINDINGS

Adult C57BL/6 mice underwent ovariectomies or sham surgeries to remove circulating estrogens. These mice were implanted with placebo or 17beta-estradiol pellets acutely or chronically. A separate experiment examined mice that received weekly injections of Faslodex to chronically block ERs. Skeletal muscles were analyzed for expression of ER genes and proteins and antioxidant genes. ERalpha was the most abundant, followed by Gper and ERbeta in both soleus and EDL muscles. The loss of estrogens through ovariectomy induced ERalpha gene and protein expression in the soleus, EDL, and TA muscles at both the acute and chronic time points. Gpx3 mRNA was also induced both acutely and chronically in all 3 muscles in mice receiving 17beta-estradiol. When ERs were blocked using Faslodex, Gpx3 mRNA was downregulated in the soleus muscle, but not the EDL and TA muscles.

CONCLUSIONS/SIGNIFICANCE

These data suggest that Gpx3 and ERalpha gene expression are sensitive to circulating estrogens in skeletal muscle. ERs may regulate Gpx3 gene expression in the soleus muscle, but skeletal muscle regulation of Gpx3 via ERs is dependent upon muscle type. Further work is needed to determine the indirect effects of estrogen and ERalpha on Gpx3 expression in skeletal muscle, and their importance in the aging process.