Impaired PI3 K Akt expression in liver and skeletal muscle of ovariectomized rats

Estrogen-mediated oar-miR-485-5p targets PPP1R13B to regulate myoblast proliferation in sheep

Ovaries are important endocrine organs in female animals that secrete various steroid hormones, which are involved in multiple physiological functions. Estrogen, one of the hormones secreted by ovaries, is essential for the overall maintenance of muscle growth and development. However, the molecular mechanisms that affect muscle growth and development in sheep following ovariectomy remain unclear. In this study, we identified 1662 differentially expressed mRNAs (DEGs) and 40 differentially expressed miRNAs (DEMs) in sheep that underwent ovariectomy compared with those that underwent sham surgery. A total of 178 DEG-DEM pairs were negatively correlated. GO and KEGG analysis showed that PPP1R13B was involved in the PI3K-Akt signaling pathway, which was essential for muscle development. Using in vitro experiments, we examined the effect of PPP1R13B on myoblast proliferation and found that overexpression or inhibition of PPP1R13B increased or decreased the expression of myoblast proliferation markers, respectively. PPP1R13B was identified as a functional downstream target of miR-485-5p. Our results suggested that miR-485-5p promoted myoblast proliferation by regulating proliferation factors in myoblasts by targeting PPP1R13B. Notably, exogenous estradiol supplementation to myoblasts regulated the expression of oar-miR-485-5p and PPP1R13B and promoted myoblast proliferation. These results provided new insights into the molecular mechanism by which ovaries influence muscle growth and development in sheep.

Mechanisms of Estrogen Influence on Skeletal Muscle: Mass, Regeneration, and Mitochondrial Function

Human menopause is widely associated with impaired skeletal muscle quality and significant metabolic dysfunction. These observations pose significant challenges to the quality of life and mobility of the aging population, and are of relevance when considering the significantly greater losses in muscle mass and force-generating capacity of muscle from post-menopausal females relative to age-matched males. In this regard, the influence of estrogen on skeletal muscle has become evident across human, animal, and cell-based studies. Beneficial effects of estrogen have become apparent in mitigation of muscle injury and enhanced post-damage repair via various mechanisms, including prophylactic effects on muscle satellite cell number and function, as well as membrane stability and potential antioxidant influences following injury, exercise, and/or mitochondrial stress. In addition to estrogen replacement in otherwise deficient states, exercise has been found to serve as a means of augmenting and/or mimicking the effects of estrogen on skeletal muscle function in recent literature. Detailed mechanisms behind the estrogenic effect on muscle mass, strength, as well as the injury response are beginning to be elucidated and point to estrogen-mediated molecular cross talk amongst signalling pathways, such as apoptotic signaling, contractile protein modifications, including myosin regulatory light chain phosphorylation, and the maintenance of muscle satellite cells. This review discusses current understandings and highlights new insights regarding the role of estrogen in skeletal muscle, with particular regard to muscle mass, mitochondrial function, the response to muscle damage, and the potential implications for human physiology and mobility.

The advantages of physical exercise as a preventive strategy against NAFLD in postmenopausal women

BACKGROUND

The prevalence and severity of nonalcoholic fatty liver disease (NAFLD) increase in women after menopause. This narrative review discusses the causes and consequences of NAFLD in postmenopausal women and describes how physical activity can contribute to its prevention.

METHODS

The authors followed the narrative review method to perform a critical and objective analysis of the current knowledge on the topic. The Medical Subject Heading keywords 'physical exercise', 'menopause', 'hormone replacement therapy', 'estradiol' and 'NAFLD' were used to establish a conceptual framework. The databases used to collect relevant references included Medline and specialized high-impact journals.

RESULTS

Higher visceral adiposity, higher rate of lipolysis in adipose tissue after oestrogen drop and changes in the expression of housekeeping proteins involved in hepatic lipid management are observed in women after menopause, contributing to NAFLD. Excessive liver steatosis leads to hepatic insulin resistance, oxidative stress and inflammation, accelerating NAFLD progression. Physical activity brings beneficial effects against several postmenopausal-associated complications, including NAFLD progression. Aerobic and resistance exercises partially counteract alterations induced by metabolic syndrome in sedentary postmenopausal women, impacting NAFLD progression and severity.

CONCLUSIONS

With the increased global obesity epidemic in developing countries, NAFLD is becoming a severe problem with increased prevalence in women after menopause. Evidence shows that physical activity may delay NAFLD development and severity in postmenopausal women, although the prescription of age-appropriate physical activity programmes is advisable to assure the health benefits.

17β-estradiol ameliorates lipotoxicity-induced hepatic mitochondrial oxidative stress and insulin resistance

The prevalence and severity of nonalcoholic fatty liver disease (NAFLD) is higher in men and postmenopausal women compared to premenopausal women, suggesting a protective role for ovarian hormones. Diet-induced obesity and fatty acids surplus promote mitochondrial dysfunction in liver, triggering oxidative stress and activation of c-Jun N-terminal kinase (JNK) which has been related to the development of insulin resistance and steatosis, the main hallmarks of NAFLD. Considering that estrogen, in particular 17β-estradiol (E2), have been reported to improve mitochondrial biogenesis and function in liver, our aim was to elucidate the role of E2 in preventing fatty acid-induced insulin resistance in hepatocytes through modulation of mitochondrial function, oxidative stress and JNK activation. An in vivo study was conducted in Wistar rats of both sexes (n = 7) fed control diet and high-fat diet (HFD), and in vitro studies were carried out in HepG2 cells treated with palmitate (PA) and E2 for 24 h. Our HFD-fed male rats showed a prediabetic state characterized by greater systemic and hepatic insulin resistance, as well as higher lipid content in liver, compared to females. JNK activation rose markedly in males in response to HFD feeding, in parallel with mitochondrial dysfunction and oxidative stress. Consistently, in PA-exposed HepG2 cells, E2 treatment prevented JNK activation, insulin resistance and fatty acid accumulation. Altogether, our data highlights the importance of E2 as a mitigating factor of fatty acid-insulin resistance in hepatocytes through downregulation of JNK activation, by means of mitochondrial function improvement.

Ovariectomy and obesity have equal impact in causing mitochondrial dysfunction and impaired skeletal muscle contraction in rats

OBJECTIVE

Previous studies have demonstrated that either an obese-insulin resistance condition or a condition involving loss of estrogen impaired skeletal muscle function as indicated by a decrease in muscle contraction. The differing effects of combined estrogen deficiency over obese-insulin resistance on skeletal muscle function have, however, not yet been determined. Our hypothesis was that estrogen deficiency aggravates skeletal muscle dysfunction in obese-insulin resistant rats, via increased muscle oxidative stress and mitochondrial dysfunction.

METHODS

Twenty-four female Wistar rats were divided into 2 groups and animals in each group were fed either a normal diet (ND) or a high-fat diet (HFD) for 24 weeks. At week 13, rats in each group were subdivided into 2 subgroups: sham-operated or ovariectomized (n = 6/subgroup). At the end of the experimental period the contraction of the gastrocnemius muscles was tested before the rats were sacrificed. Skeletal muscle was removed to assess oxidative stress and mitochondrial function.

RESULTS

We found that an obese-insulin resistant condition was observed in sham-operated HFD-fed rats, ovariectomized ND-fed rats, and ovariectomized HFD-fed rats. Skeletal muscle contractile function (peak-force ratio [g/g]; 25.40 ± 2.03 [ovariectomized ND-fed rats], 22.44 ± 0.85 [sham-operated HFD-fed rats] and 25.06 ± 0.61 [ovariectomized HFD-fed rats]), skeletal muscle mitochondrial function, and oxidative stress were equally significantly impaired in all 3 groups, when compared with those of sham-operated ND-fed rats (31.12 ± 1.88 g/g [NDS]; P < 0.05). Surprisingly, loss of estrogen did not aggravate these dysfunctions of skeletal muscles in HFD-fed rats.

CONCLUSIONS

These findings suggest that skeletal muscle dysfunction may occur due to increased muscle oxidative stress and mitochondrial dysfunction as a result of ovariectomy and obese-insulin resistance. Loss of estrogen, however, did not aggravate these impairments in the muscle of rats with obese-insulin resistant condition.

Pancreastatin inhibitor, PSTi8 ameliorates metabolic health by modulating AKT/GSK-3β and PKCλ/ζ/SREBP1c pathways in high fat diet induced insulin resistance in peri-/post-menopausal rats

Increase in the prevalence of insulin resistance (IR) in peri-/post-menopause women is mainly due to hormone deficiency and lifestyle. PSTi8 (PEGKGEQEHSQQKEEEEEMAV-amide) is a pancreastatin inhibitor peptide which showed potent antidiabetic activity in genetic and lifestyle induced type 2 diabetic mice. In the present work, we have investigated the antidiabetic activity of PSTi8 in rat models of peri-/post-menopausal IR. 4-vinylcyclohexenediepoxide treated and ovariectomized rats were fed with high fat diet for 12 weeks to develop the peri-/post-menopausal IR. PSTi8 peptide was administered after the development of peri-/post-menopausal IR rats. PSTi8 (1 mg/kg, i.p) improved the glucose homeostasis which is characterized by elevated glycogenesis, enhanced glycolysis and reduced gluconeogenesis. PSTi8 suppressed palmitate- and PST- induced IR in HepG2 cells. PSTi8 treatment enhanced energy expenditure in peri-/post-menopausal IR rats. PSTi8 treatment increased insulin sensitivity in peri-/post-menopausal IR rats, may be mediated by modulating IRS1-2-phosphatidylinositol-3-kinase-AKT-GSK3β and IRS1-2-phosphatidylinositol-3-kinase-PKCλ/ζ-SREBP1c signaling pathways in the liver. PSTi8 can act as a potential therapeutic peptide for the treatment of peri-/post-menopausal IR.

Undercarboxylated Osteocalcin Improves Insulin-Stimulated Glucose Uptake in Muscles of Corticosterone-Treated Mice

Short-term administration of glucocorticoids (GCs) impairs muscle insulin sensitivity at least in part via the reduction of undercarboxylated osteocalcin (ucOC). However, whether ucOC treatment reverses the GC-induced muscle insulin resistance remains unclear. To test the hypothesis that ucOC directly ameliorates impaired insulin-stimulated glucose uptake (ISGU) induced by short-term GC administration in mice muscle and to identify the molecular mechanisms, mice were implanted with placebo or corticosterone (CS) slow-release pellets. Two days post-surgery, insulin-tolerance tests (ITTs) were performed. On day 3, serum was collected and extensor digitorum longus (EDL) and soleus muscles were isolated and treated ex vivo with vehicle, ucOC (30 ng/mL), insulin (60 µU/mL), or both. Circulating hormone levels, muscle glucose uptake, and muscle signaling proteins were assessed. CS administration reduced both serum osteocalcin and ucOC levels, whole-body insulin sensitivity, and muscle ISGU in EDL. Ex vivo ucOC treatment restored ISGU in CS-affected muscle, without increasing non-insulin-stimulated glucose uptake. In CS-affected EDL muscle, ucOC enhanced insulin action on phosphorylated (p-)protein kinase B (Akt)^Ser473 and the p-extracellular signal-regulated kinase isoform 2 (ERK2)^{Thr202/Tyr204} /total (t)ERK2 ratio, which correlated with ISGU. In CS-affected soleus muscle, ucOC enhanced insulin action on p-mammalian target of rapamycin (mTOR)^Ser2481 , the p-mTOR^Ser2481 /tmTOR ratio, p-Akt substrate of 160kD (AS160)^Thr642 , and p-protein kinase C (PKC) (pan)^Thr410 , which correlated with ISGU. Furthermore, p-PKC (pan)^Thr410 correlated with p-Akt^Ser473 and p-AS160^Thr642 . ucOC exerts direct insulin-sensitizing effects on CS-affected mouse muscle, likely through an enhancement in activity of key proteins involved in both insulin and ucOC signaling pathways. Furthermore, these effects are muscle type-dependent. © 2019 American Society for Bone and Mineral Research.

Dendrobium mixture regulates hepatic gluconeogenesis in diabetic rats via the phosphoinositide-3-kinase/protein kinase B signaling pathway

The present study aimed to evaluate the impact of dendrobium mixture (DMix) on the gene and protein expression of insulin signaling pathway-associated factors in the livers of diabetic rats. The molecular mechanisms by which DMix inhibits gluconeogenesis were also investigated. A total of 47 female Wistar rats were used in the present study. Of these, 11 rats were randomly selected as healthy controls and diabetes was induced in the remaining 36 rats by administering a high-fat and high-sugar diet for 6 weeks, followed by two intraperitoneal injections of streptozotocin. The 36 rats were screened for diabetes and then randomly divided into three groups: Model, metformin and DMix groups. Following 12 weeks of treatment, the fasting blood glucose (FBG), glycosylated serum protein (GSP), serum insulin, blood lipids [total cholesterol (Tch) and triglycerides (TG)], alanine transaminase (ALT) and aspartate transaminase (AST) were assessed. In addition, hematoxylin and eosin staining was used for histomorphological examination of the liver tissues. The mRNA expression of insulin receptor (InsR), forkhead box protein O1 (FoxO1), phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6-phosphatase (G6Pase) in the liver was measured with reverse transcription-quantitative polymerase chain reaction and the protein expression of InsR, phosphoinositide-3-kinase (PI3K), phosphorylated (p)-PI3K, protein kinase B (Akt), p-Akt, FoxO1, PEPCK and G6Pase in the liver was measured by western blot analysis. The FBG, GSP, InsR, Tch, TG, ALT and AST levels were significantly lower in the DMix-treated group compared with the model group (P<0.05). In addition, DMix treatment notably improved liver histopathology and significantly increased the gene and protein expression of InsR, PI3K and Akt (P<0.05). DMix treatment also significantly reduced the gene and protein expression of FoxO1, PEPCK and G6Pase (P<0.05). DMix effectively reduced FBG and blood lipids and significantly improved liver function and insulin resistance in diabetic rats, possibly by regulating the gene and protein expression of molecules associated with the PI3K/Akt signaling pathway.

Dehydroepiandrosterone supplementation is not beneficial in the late postmenopausal period in diet-induced obese rats

AIMS

Dehydroepiandrosterone (DHEA) is an adrenal steroid hormone that is a precursor of sexual hormones. It is reduced during aging and is strongly associated with insulin resistance and obesity. There is evidence for beneficial effects of this steroid, in both human and animal models, during perimenopause. However, the impact of DHEA treatment during late postmenopause on glucose metabolism is not clearly documented. We tested the hypothesis that DHEA supplementation could improve insulin sensitivity in an ovariectomized obese rat model (OVX) that was fed a high-fat diet for 11 weeks.

MAIN METHODS

Female Wistar rats at 8 weeks of age were OVX or SHAM-operated. Eight weeks after the surgery, the animals were randomly treated with vehicle or DHEA for 3 weeks. Food intake, metabolic parameters and insulin sensitivity were evaluated.

KEY FINDINGS

Following the ovariectomy, increased body weight gain, adiposity index, and feeding efficiency were observed, despite there being no change in food and energy intake. The OVX rats also displayed glucose intolerance, insulin resistance, decreased insulin-induced IRS1/2 tyrosine phosphorylation in the skeletal muscle, and reduced serum VLDL-c and TAG levels. OVX rats treated with 10 mg/kg DHEA (OVX + DHEA) exhibited estradiol (E₂) serum levels similar to SHAM animals, with no change in uterus mass. DHEA treatment also resulted in an increase in energy intake.

SIGNIFICANCE

Despite the positive effects of DHEA supplementation observed in menopausal women and ovariectomized rats, a potential negative effect on glucose metabolism and insulin action in the late postmenopausal condition in diet-induced obese OVX rats are reported.