Metformin enhances the action of insulin on porcine granulosa-lutein cells in vitro

Insulin regulates gap junction intercellular communication in porcine granulosa cells through modulation of connexin43 protein expression

Gap junction intercellular communication (GJIC) among granulosa cells plays an important role in folliculogenesis, and it is temporal-spatially regulated during follicular development. Connexin (Cx) proteins predominantly form the basal structure of gap junctions in granulosa cells. In our study, immunohistochemical analysis revealed that Cx43 is the most widely expressed connexin in porcine follicles, especially among the large antral follicles. With application of insulin on porcine granulosa cells, we found that insulin significantly facilitated the protein level of Cx43, not mRNA level. This process is dependent on the phosphorylated activities of AKT and Erk since selective AKT and Erk inhibitors, LY294002 and U0126, respectively, hampered the potential of insulin to up-regulate Cx43 protein expression. As a consequence, the insulin-enhanced Cx43-couple GJIC activity in porcine granulosa cells was corresponding attenuated by the administration of LY294002 and U0126. Our findings provide a new insight into the molecular mechanisms by which insulin mediates cell-cell communication in porcine granulosa cells and sheds light on nutrition-reproduction interactions.

Network pharmacology and metabolomics study on the intervention of traditional Chinese medicine Huanglian Decoction in rats with type 2 diabetes mellitus

ETHNOPHARMACOLOGICAL RELEVANCE

Type 2 diabetes mellitus (T2DM) is currently one of the most prominent and global chronic conditions. Huanglian Decoction (HLD) is a traditional Chinese medicine (TCM) preparation that has been used to treat T2DM for thousands of years in China. However, its mechanism of action at the metabolic level is still unclear. The purpose of this work is to study the mechanism of HLD in treating T2DM based on metabolomics and network pharmacology.

MATERIALS AND METHODS

In this study, metabolomics combined with network pharmacology was used to elucidate the therapeutic mechanism of HLD in T2DM. Serum samples were collected from rats with T2DM, induced by a high-sugar and high-fat diet combined with streptozotocin (STZ), to measure the levels of biochemical markers. Urinary metabolomics-based analysis using high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) was conducted to evaluate the differential metabolites from multiple metabolic pathways.

RESULTS

After treatment with HLD for 4 weeks, biochemical indicators, including fasting blood glucose (FBG), blood lipid, fasting insulin (FINS), insulin sensitivity index (ISI), and homeostasis model assessment of insulin resistance (HOMA-IR), were significantly improved. Metabolomics results revealed that HLD regulated the biomarkers, such as cytosine, L-carnitine, betaine, phenylalanine, glucose, citrate, phenylpyruvate, and hippuric acid in glyoxylate and dicarboxylate metabolism, phenylalanine metabolism, and tricarboxylic acid (TCA) cycle. The combination of network pharmacology, metabolomics, western blot, and PCR showed that HLD can treat T2DM by enhancing the gene and protein expression levels of glucose transporter 4 (GLUT4), insulin receptor (INSR), and mitogen-activated protein kinase 1 (MAPK1) to interfere with glyoxylate and dicarboxylate metabolism.

CONCLUSIONS

The study based on metabolomics and network pharmacology indicated that HLD can improve T2DM through multiple targets and pathways, and it may be a useful alternative therapy for the treatment of T2DM.

Histomorphological, VEGF and TGF-β immunoexpression changes in the diabetic rats' ovary and the potential amelioration following treatment with metformin and insulin

Diabetes mellitus (DM) affects the ovary by reducing the number and diameters of ovarian follicles and increasing atretic follicles. Follicular growth and diameters depend on VEGF production. Hyperglycemia causes ovarian stromal and follicular degeneration then fibrosis by activating TGF-β. Insulin and metformin promote development of ovarian follicles and reduce atretic follicles. Therefore, the present study investigates the ovarian VEGF and TGF-β immune-expression and its variations in diabetic, insulin and metformin-treated rats. Forty adult female albino rats were divided equally into four groups: control, diabetic (STZ-induced diabetes), diabetic metformin-treated group (100 mg/kg/day orally/eight weeks) and diabetic insulin-treated group (5 U insulin /day). Ovarian sections were stained with hematoxylin and eosin, Masson's trichrome, immunohistochemistry for VEGF and TGF-β. The diabetic group showed noticeable atrophic and degenerative changes in cortex and medulla as well as increased density and distribution of the collagenous fibers. The number and diameter of primary, secondary and tertiary follicles were decreased. However, the number of atretic follicles and corpus luteum was increased. Significant decrease in the surface area percentage of VEGF immuno-expression and significant increase in TGF-β immuno-expression surface area percentage were detected. By treating animals with metformin and insulin, there was restoration of the ovarian histological structure more or less as in control. DM negatively affects the histological and morphometric parameters of ovaries. Furthermore, insulin showed more beneficial effects than metformin in hindering these complications by modifying the expression of VEGF and TGF-β.

Metformin has a direct effect on ovarian cells that is dependent on organic cation transporters

Metformin (MET) is the most widely prescribed hypoglycemic drug in type 2 diabetes and Polycystic Ovary Syndrome. Besides its effects on glucose metabolism, MET exerts beneficial effects on these patients' fertility. However, the exact mechanisms of action of MET on female fertility are still unclear. In this work, we analyzed a possible direct effect of MET on ovarian cells. We found expression of the organic cation transporters OCT1, OCT2 and OCT3, responsible for MET uptake into the cells, in rat granulosa cells and human cumulus cells. Furthermore, MET increased pAMPK and decreased VEGF levels both in vivo and in rat granulosa cells in culture. These last effects were reversed when OCTs were inhibited. Our results suggest that MET acts directly on ovarian cells regulating cell metabolism and VEGF expression. Our findings are relevant to optimize PCOS fertility treatment and to explore ovarian MET actions in other female pathologies.

DHEA-induced ovarian hyperfibrosis is mediated by TGF-β signaling pathway

Background

The polycystic ovary syndrome (PCOS) is a common metabolic and endocrine disorder with pathological mechanisms remain unclear. The following study investigates the ovarian hyperfibrosis forming via transforming growth factor-β (TGF-β) signaling pathway in Dehydroepiandrosterone (DHEA)- induced polycystic ovary syndrome (PCOS) rat model. We furthermore explored whether TGF-βRI inhibitor (SB431542) decreases ovarian fibrosis by counterbalancing the expression of fibrotic biomarkers.

Methods

Thirty female Sprague-Dawley rats were randomly divided into Blank group (n = 6), Oil group (n = 6), and Oil + DHEA-induced model group (n = 6 + 12). The model groups were established by subcutaneous injection of DHEA for 35 consecutive days. The 12 successful model rats were additionally divided in vehicle group (n = 6) and SB431542-treated group (n = 6). Vehicle group and SB431542-treated group, served as administration group and were intraperitoneally injected with DMSO and SB431542 for additional 14 consecutive days. Ovarian morphology, fibrin and collagen localization and expression in ovaries were detected using H&E staining, immunohistochemistry and Sirius red staining. The ovarian protein and RNA were examined using Western blot and RT-PCR.

Results

In DHEA-induced ovary in rat, fibrin and collagen had significantly higher levels, while the main fibrosis markers (TGF-β, CTGF, fibronectin, a-SMA) were obviously upregulated. SB431542 significantly reduced the expression of pro-fibrotic molecules (TGF-β, Smad3, Smad2, a-SMA) and increased anti-fibrotic factor MMP2.

Conclusion

TGF-βRI inhibitor (SB431542) inhibits the downstream signaling molecules of TGF-β and upregulates MMP2, which in turn prevent collagen deposition. Moreover, ovarian hyperfibrosis in DHEA-induced PCOS rat model could be improved by TGF-βRI inhibitor (SB431542) restraining the transcription of accelerating fibrosis genes and modulating EMT mediator.

Electronic supplementary material

The online version of this article (10.1186/s13048-017-0375-7) contains supplementary material, which is available to authorized users.

Insulin signalling and glucose transport in the ovary and ovarian function during the ovarian cycle

Data derived principally from peripheral tissues (fat, muscle and liver) show that insulin signals via diverse interconnecting intracellular pathways and that some of the major intersecting points (known as critical nodes) are the IRSs (insulin receptor substrates), PI3K (phosphoinositide kinase)/Akt and MAPK (mitogen-activated protein kinase). Most of these insulin pathways are probably also active in the ovary and their ability to interact with each other and also with follicle-stimulating hormone (FSH) and luteinizing hormone (LH) signalling pathways enables insulin to exert direct modulating influences on ovarian function. The present paper reviews the intracellular actions of insulin and the uptake of glucose by ovarian tissues (granulosa, theca and oocyte) during the oestrous/menstrual cycle of some rodent, primate and ruminant species. Insulin signals through diverse pathways and these are discussed with specific reference to follicular cell types (granulosa, theca and oocyte). The signalling pathways for FSH in granulosa cells and LH in granulosa and theca cells are summarized. The roles of glucose and of insulin-mediated uptake of glucose in folliculogenesis are discussed. It is suggested that glucose in addition to its well-established role of providing energy for cellular function may also have insulin-mediated signalling functions in ovarian cells, involving AMPK (AMP-dependent protein kinase) and/or hexosamine. Potential interactions of insulin signalling with FSH or LH signalling at critical nodes are identified and the available evidence for such interactions in ovarian cells is discussed. Finally the action of the insulin-sensitizing drugs metformin and the thiazolidinedione rosiglitazone on follicular cells is reviewed.

Modulation of gonadotrophin induced steroidogenic enzymes in granulosa cells by d-chiroinositol

BACKGROUND

d-chiroinositol (DCI) is a inositolphosphoglycan (IPG) involved in several cellular functions that control the glucose metabolism. DCI functions as second messenger in the insulin signaling pathway and it is considered an insulin sensitizer since deficiency in tissue availability of DCI were shown to cause insulin resistance (IR). Polycystic ovary syndrome (PCOS) is a pathological condition that is often accompanied with insulin resistance. DCI can positively affects several aspect of PCOS etiology decreasing the total and free testosterone, lowering blood pressure, improving the glucose metabolism and increasing the ovulation frequency. The purpose of this study was to evaluate the effects of DCI and insulin combined with gonadotrophins namely follicle-stimulating hormone (FSH) and luteinizing hormone (LH) on key steroidogenic enzymes genes regulation, cytochrome P450 family 19 subfamily A member 1 (CYP19A1) and cytochrome P450 side-chain cleavage (P450scc) in primary cultures of human granulosa cells (hGCs). We also investigated whether DCI, being an insulin-sensitizer would be able to counteract the expected stimulator activity of insulin on human granulosa cells (hGCs).

METHODS

The study was conducted on primary cultures of hGCs. Gene expression was evaluated by RT-qPCR method. Statistical analysis was performed applying student t-test, as appropriate (P < 0.05) set for statistical significance.

RESULTS

DCI is able to reduce the gene expression of CYP19A1, P450scc and insulin-like growth factor 1 receptor (IGF-1R) in dose-response manner. The presence of DCI impaired the increased expression of steroidogenic enzyme genes generated by the insulin treatment in gonadotrophin-stimulated hGCs.

CONCLUSIONS

Insulin acts as co-gonadotrophin increasing the expression of steroidogenic enzymes genes in gonadotrophin-stimulated granulosa cells. DCI is an insulin-sensitizer that counteracts this action by reducing the expression of the genes CYP19A1, P450scc and IGF-1R. The ability of DCI to modulate in vitro ovarian activity of insulin could in part explain its beneficial effect when used as treatment for conditions associated to insulin resistance.

The effect of metformin treatment in vivo on acute and long-term energy metabolism and progesterone production in vitro by granulosa cells from women with polycystic ovary syndrome

STUDY QUESTION

What are the consequences of polycystic ovary syndrome (PCOS) pathology and metformin-pretreatment in vivo in women with PCOS on the metabolism and steroid production of follicular phenotype- and long-term cultured-granulosa cells (GC)?

SUMMARY ANSWER

PCOS pathology significantly compromised glucose metabolism and the progesterone synthetic capacity of follicular- and long-term cultured-GCs and the metabolic impact of PCOS on GC function was alleviated by metformin-pretreatment in vivo.

WHAT IS KNOWN ALREADY

Granulosa cells from women with PCOS have been shown to have an impaired insulin-stimulated glucose uptake and lactate production in vitro. However, these results were obtained by placing GCs in unphysiological conditions in culture medium containing high glucose and insulin concentrations. Moreover, existing data on insulin-responsive steroid production in vitro by PCOS GCs vary.

STUDY DESIGN, SIZE AND DURATION

Case-control experimental research comparing glucose uptake, pyruvate and lactate production and progesterone production in vitro by GCs from three aetiological groups, all undergoing IVF; healthy control women (Control, n = 12), women with PCOS treated with metformin in vivo (Metformin, n = 8) and women with PCOS not exposed to metformin (PCOS, n = 8). The study was conducted over a period of 3 years between 2007 and 2010.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Rotterdam criteria were used for the diagnosis of PCOS; all subjects were matched for age, BMI and baseline FSH. Individual patient cultures were undertaken with cells incubated in a validated, physiological, serum-free culture medium containing doses of 0–6 mM glucose and 0–100 ng/ml insulin for 6 h and 144 h to quantify the impact of treatments on acute and long-term metabolism, respectively, and progesterone production. The metabolite content of spent media was measured using spectrophotometric plate reader assay. The progesterone content of spent media was measured by enzyme-linked immunosorbent assay. Viable GC number was quantified after 144 h of culture by the vital dye Neutral Red uptake assay.

MAIN RESULTS AND THE ROLE OF CHANCE

Granulosa cells from women with PCOS pathology revealed reduced pyruvate production and preferential lactate production in addition to their reduced glucose uptake during cultures (P < 0.05). Metformin pretreatment alleviated this metabolic lesion (P < 0.05) and enhanced cell proliferation in vitro (P < 0.05), but cells retained a significantly reduced capacity for progesterone synthesis compared with controls (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

Although significant treatment effects were detected in this small cohort, further studies are required to underpin the molecular mechanisms of the effect of metformin on GCs.

WIDER IMPLICATIONS OF THE FINDINGS

The individual patient culture strategy combined with multifactorial experimental design strengthens the biological interpretation of the data. Collectively, these results support the notion that there is an inherent impairment in progesterone biosynthetic capacity of the GCs from women with PCOS. The positive, acute metabolic effect and the negative long-term steroidogenic effect on GCs following metformin exposure in vivo may have important implications for follicular development and luteinized GC function when the drug is used in clinical practice.

STUDY FUNDING/COMPETING INTEREST(S)

No competing interests. This work was supported by the UK Medical Research Council Grant Reference number G0800250.