Expression of insulin-receptor substrate-1 and -2 in ovaries from women with insulin resistance and from controls

Molecular crosstalk between insulin-like growth factors and follicle-stimulating hormone in the regulation of granulosa cell function

Background

The last phase of folliculogenesis is driven by follicle-stimulating hormone (FSH) and locally produced insulin-like growth factors (IGFs), both essential for forming preovulatory follicles.

Methods

This review discusses the molecular crosstalk of the FSH and IGF signaling pathways in regulating follicular granulosa cells (GCs) during the antral-to-preovulatory phase.

Main findings

IGFs were considered co-gonadotropins since they amplify FSH actions in GCs. However, this view is not compatible with data showing that FSH requires IGFs to stimulate GCs, that FSH renders GCs sensitive to IGFs, and that FSH signaling interacts with factors downstream of AKT to stimulate GCs. New evidence suggests that FSH and IGF signaling pathways intersect at several levels to regulate gene expression and GC function.

Conclusion

FSH and locally produced IGFs form a positive feedback loop essential for preovulatory follicle formation in all species. Understanding the mechanisms by which FSH and IGFs interact to control GC function will help design new interventions to optimize follicle maturation, perfect treatment of ovulatory defects, improve in vitro fertilization, and develop new contraceptive approaches.

Association of insulin receptor substrate 1 (IRS-1) gene polymorphism with growth and litter-related traits in NMER rabbits

This study investigated the associations between the c.189G > T polymorphism of the insulin receptor substrate-1 (IRS-1) gene and the growth and litter size-related traits in the Native rabbit in Middle Egypt (NMER). One hundred sixty-two NMER rabbits were genotyped by RFLP-PCR using Sau3AI restriction enzyme and the associations of the reported genotypes with body weights at 5th, 6th, 8th, 10th, and 12th week old, body gain, and daily gain plus, the litter size-related traits were determined. Additionally, the genotypic and allelic frequencies, the effective (Ne) and observed (NA) numbers of alleles, observed (Ho) and expected (He) heterozygosity, Hardy-Weinberg equilibrium (HWE), and the decrease in heterozygosity because of inbreeding (FIS) were calculated. Three genotypes; GG, GT, and TT with 0.65, 0.33, and 0.02 frequencies, respectively which fit HWE were reported. These genotypes displayed a marked low FIS value. Significant associations of the genotypes with the body weights, and gains, except at the 5th week old determined with superiority of the GT genotype compared with the other genotypes. All reported litter size-related traits significantly varied among different genotypes. In summary, the c.189G > T SNP of the IRS-1 gene is an effective genetic marker to improve growth performance and litter size traits of the NMER rabbits.

LncRNA NEAT1 and MALAT1 are involved in polycystic ovary syndrome pathogenesis by functioning as competing endogenous RNAs to control the expression of PCOS-related target genes

Accumulating evidence has shown an abnormal expression of several non-coding RNAs in ovarian tissues which might be closely linked with the pathogenesis of PCOS. The aim of this study was to identify competing endogenous (ce) RNA network: long non-coding RNA (lncRNA), microRNA (miRNA) and their target genes: androgen receptor (AR), follistatin (FST) and insulin receptor substrate-2 (IRS-2), which are relevant to PCOS, to underline the molecular pathogenesis of PCOS and assist in early diagnosis and treatment. Bioinformatic analysis was performed to retrieve a ceRNA network: [lncRNA (NEAT1 and MALAT1) - miRNA (miR-30a-5p and miR-30d-5p) - mRNA (AR, FST and IRS-2)] linked to PCOS. Expression of the selected RNAs was examined by qPCR in peripheral blood leukocytes obtained from 73 PCOS patients (41 obese and 32 non-obese) and 31 healthy controls. PCOS patients showed significantly higher expression levels of NEAT1, miR-30a-5p, AR, FST and IRS-2, with significantly lower expression levels of MALAT1 and miR-30d-5p relative to controls especially in obese versus non-obese patients. Receiver operating characteristic (ROC) curve analysis indicated that most of the selected RNAs could serve as potential early diagnostic markers for PCOS with the highest efficiency obtained upon combining NEAT1 and miR-30d-5p or MALAT1 and miR-30a-5p with either of PCOS target genes. Moreover, all addressed RNAs had been proved as potential predictors of PCOS. The obtained data of ceRNA network raised the possibility that NEAT1 overexpression may increase the expression levels of AR, FST and IRS-2 by sponging miR-30d-5p, while low expression of MALAT1 may allow higher expression of the above genes via increasing miR-30a-5p, suggesting their involvement in PCOS pathogenesis and promising role for future diagnosis and targeted therapy.

Expression of IRS2 in the female reproductive system during the estrous cycle in mice

Insulin receptor substrate 2 (IRS2) participates in reproduction; however, the location and expression of IRS2 in the reproductive system of female mice is not clear. We used real-time quantitative polymerase chain reaction (RT-PCR), western blot and immunohistochemical staining to investigate the expression of IRS2 in the ovary, oviduct and uterus of female mice during the estrous cycle. We found that IRS2 was expressed in all reproductive organs of mouse and that the expression level changed with the estrous phases. The expression of IRS2 in reproductive organs was greatest during estrus.

The reproductive endocrine feature and conception outcome of women with unknown etiological menstrual cycle (36-45 days) with long follicular phase

OBJECTIVE

To explore the reproductive endocrine feature and conception outcome of women with unknown etiological long menstrual cycle (LMC) (36-45 days) with long follicular phase.

METHODS

In the cohort study, we included 80 women with unknown etiological long menstrual cycle of biphasic basal body temperature (BBT) lasting for 36-45 days and 87 controls with normal cycle of biphasic BBT into LMC group and NMC group, respectively. Serum hormone levels, fasting glucose, and insulin of participants were tested, and ovulation was observed by ultrasound. The conception outcome was followed up within 12 menstrual cycles.

RESULTS

In the LMC group, the rate of abnormality of HOMA-insulin resistance index (40.0% vs. 20.7%, p < .01), luteal phase defect (30.9% vs. 13.8%, p < .05) and abnormality of FSH/LH ratio (15.6% vs. 5.7%, p < .05) were all significantly higher, but the serum estradiol level on the day before ovulation (261.10 pg/mL vs. 320.26 pg/mL, p < .01) was lower. The rate of poor ovulation quality (31.3% vs.15.4%, p < .05) in the LMC group was significantly higher than the NMC group. In the LMC group, the natural conception rate within 12 menstrual cycles was lower (41.9% vs. 66.2%, p < .01), whereas the spontaneous abortion rate in early pregnancy (29.0% vs. 9.8%, p < .05) and the conversion rate (21.6% vs. 5.2%, p < .01) to anovulation within 12 cycles were significantly higher.

CONCLUSIONS

Women with unknown etiological menstrual cycle (36-45 days) with long follicular phase have greater endocrine abnormality and higher risk of spontaneous abortion, infertility, and conversion to anovulation. Moderate early intervention may be advisable for these women, especially those who wish to get pregnant.

Network pharmacology integrated with experimental validation reveals the regulatory mechanism of action of Hehuan Yin decoction in polycystic ovary syndrome with insulin resistance

ETHNOPHARMACOLOGICAL RELEVANCE

Hehuan Yin decoction (HHY), first recorded in the Jingyue Quanshu (published in 1624 A.D.), is composed of Albizia julibrissin Durazz. and Ampelopsis japonica (Thunb.) Makino.

AIM OF THE STUDY

This study aimed to investigate the mechanism of action of HHY in treating polycystic ovary syndrome with insulin resistance (PCOS-IR).

MATERIALS AND METHODS

Network pharmacology and molecular docking were used to predict active compounds, potential targets, and pathways for PCOS-IR treatment using HHY. Female Sprague-Dawley rats were administered letrozole (1 mg/kg) with a high-fat diet to establish a PCOS-IR model. Thereafter, symptoms, ovarian pathology, serum insulin resistance, and sex hormone levels were determined. Western blotting was used to determine the levels of PI3Kp85α, AKT, phospho (p)-AKT, and GSK3β in the ovaries of rats.

RESULTS

Network pharmacology revealed 58 components in HHY and 182 potential targets that were shared between HHY and PCOS-IR. HHY could potentially treat PCOS-IR via the insulin resistance, PI3K/AKT, HIF-1, and steroid hormone biosynthesis pathways. Molecular docking revealed that PI3K, AKT1, GSK3β, IRS1, and EGFR had high affinities to HHY compounds. In the PCOS-IR rats, HHY significantly normalised the symptoms and ovarian pathology, increased follicle-stimulating hormone (FSH) and oestradiol levels in the serum, and decreased the levels of fasting plasma glucose and fasting insulin, as well as the insulin resistance index. HHY also decreased the luteinising hormone (LH) and testosterone levels and the LH/FSH ratio in the PCOS-IR rats and increased the levels of PI3K, p-AKT, and GSK3β in ovary tissue, which indicated the activation of the PI3K/AKT pathway.

CONCLUSIONS

HHY can improve PCOS-IR symptoms via multiple pharmacological pathways and may be a potential alternative therapy for the treatment of PCOS-IR.

Humanin Alleviates Insulin Resistance in Polycystic Ovary Syndrome: A Human and Rat Model-Based Study

Polycystic ovary syndrome (PCOS), the most common endocrine disorder in women of reproductive age, is characterized by hyperandrogenism and insulin resistance (IR); however, the pathogenesis of local ovarian IR in PCOS remains largely unclear. Humanin, a mitochondria-derived peptide, has been reported to be associated with IR. Our previous study confirmed that humanin is expressed in multiple cell types in the ovary and is present in follicular fluid. However, it remains unknown whether humanin participates in the pathogenesis of local ovarian IR or whether humanin supplementation can improve IR in PCOS patients. In this study, we compared humanin concentrations in follicular fluid from PCOS patients with and without IR. We further investigated the effect of humanin analogue (HNG) supplementation on IR in a rat model of dehydroepiandrosterone-induced PCOS. Humanin concentrations in the follicular fluid were found to be significantly lower in PCOS patients with IR than in those without IR. HNG supplementation attenuated both the increases in the levels of fasting plasma glucose and fasting insulin in rats with PCOS and the decreases in phosphorylation of IRS1, PI3K, AKT, and GLUT4 proteins in the granulosa cells of these rats. Combined supplementation with HNG and insulin significantly improved glucose consumption in normal and humanin-siRNA-transfected COV434 cells. In conclusion, downregulated humanin in the ovaries may be involved in the pathogenesis of IR in PCOS, and exogenous supplementation with HNG improved local ovarian IR through modulation of the IRS1/PI3K/Akt signaling pathway in a rat model. This finding supports the potential future use of HNG as a therapeutic drug for PCOS.

Direct impact of gonadotropins on glucose uptake and storage in preovulatory granulosa cells: Implications in the pathogenesis of polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is often associated with higher levels of LH, and arrested ovarian follicular growth. The direct impact of high LH on FSH mediated metabolic responses in PCOS patients is not clearly understood.

METHOD

In order to investigate the impact of FSH and LH on glucose metabolism in preovulatory granulosa cells (GCs), we used [U¹⁴C]-2 deoxyglucose, D-[U¹⁴C]-glucose or 2-NBD glucose to analyse glucose uptake and its incorporation into glycogen. To reproduce the high androgenic potential in PCOS patients, we administered hCG both in vitro and in vivo. The role of IRS-2/PI3K/Akt2 pathway was studied after knockdown with specific siRNA. Immunoprecipitation and specific assays were used for the assessment of IRS-2, glycogen synthase and protein phosphatase 1. Furthermore, we examined the in vivo effects of hCG on FSH mediated glycogen increase in normal and PCOS rat model. HEK293 cells co-expressing FSHR and LHR were used to demonstrate glucose uptake and BRET change by FSH and hCG.

RESULTS

In normal human and rat granulosa cells, FSH is more potent than hCG in stimulating glucose uptake, however glycogen synthesis was significantly upregulated only by FSH through increase in activity of glycogen synthase via IRS-2/PI3K/Akt2 pathway. On the contrary, an impaired FSH-stimulated glucose uptake and glycogen synthesis in granulosa cells of PCOS-patients indicated a selective defect in FSHR activation. Further, in normal human granulosa cells, and in immature rat model, the impact of hCG on FSH responses was such that it inhibited the FSH-mediated glucose uptake as well as glycogen synthesis through inhibition of FSH-stimulated IRS-2 expression. These findings were further validated in HEK293 cells overexpressing Flag-LHR and HA-FSHR, where high hCG inhibited the FSH-stimulated glucose uptake. Notably, an increased BRET change was observed in HEK293 cells expressing FSHR-Rluc8 and LHR-Venus possibly suggesting increased heteromerization of LHR and FSHR in the presence of both hCG and FSH in comparison to FSH or hCG alone.

CONCLUSION

Our findings confirm a selective attenuation of metabolic responses to FSH such as glucose uptake and glycogen synthesis by high activation level of LHR leading to the inhibition of IRS-2 pathway, resulting in depleted glycogen stores and follicular growth arrest in PCOS patients.

Regulation of insulin resistance and glucose metabolism by interaction of PIM kinases and insulin receptor substrates

Insulin resistance is caused by various environmental and genetic factors leading to a number of serious health issues. Due to its multifactorial origin, molecular characterization may provide better tools for its effective treatment. On molecular level, dysregulation of signaling pathway by insulin receptor substrates (IRSs) is one of the most common reasons of this disease. IRSs are regulated by >50 serine/threonine kinases, which may have positive or negative effects on insulin sensitivity. Among these serine/threonine kinases, PIM kinases have garnered much attention as they not only affect insulin sensitivity by phosphorylating IRSs directly and/or indirectly but also alter the activities of their downstream molecules like PI3K, AKT, and mTOR. In this review, interactions of PIM kinases with IRSs and their downstream proteins and their action mechanism in the regulation of insulin resistance are elaborated. Furthermore, this review offers fundamental understandings of the role of PIM kinases in this signaling pathway.

Transcription profile of the insulin-like growth factor signaling pathway during human ovarian follicular development

PURPOSE

The IGF signaling cascade exerts important regulatory functions in human ovarian folliculogenesis. The scope of this study was to evaluate the transcription profile of insulin-like growth factor (IGF) genes during human ovarian follicle development and to analyze follicle fluid levels of key IGF proteins.

METHODS

Gene expression profiling was performed with microarray gene analysis. The analysis was assessed from ovarian follicles and granulosa cells (GCs) obtained from isolated stage-specific human ovarian follicles, including preantral follicles, small antral follicles, and preovulatory follicles. Numerous genes involved in the IGF signaling pathway was evaluated and key genes were validated by qPCR from GCs. Protein levels of various IGF components of human follicular fluid (FF) were measured by ELISA and time-resolved immunofluorometric assays (TRIFMA).

RESULTS

The gene expression levels of PAPPA, IGF2, IGF receptors and intracellular IGF-activated genes increased with increasing follicle size. This was especially prominent in the late preovulatory stage where IGF2 expression peaked. Protein levels of intact IGF binding protein-4 decreased significantly in FF from large preovulatory follicles compared with small antral follicles concomitant with higher protein levels of PAPP-A. The IGF modulators IGF-2 receptor, IGFBPs, stanniocalcins, and IGF-2 mRNA binding proteins were all observed to be expressed in the different follicle stages.

CONCLUSIONS

This study confirms and highlights the importance of PAPP-A regulating bioactive IGF levels throughout folliculogenesis and especially for the high rate of granulosa cell proliferation and expression of key ovarian hormones important in the last part of the follicular phase of the menstrual cycle.

Single-nucleotide polymorphism of INS, INSR, IRS1, IRS2, PPAR-G and CAPN10 genes in the pathogenesis of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common and a complex female endocrine disorder, and is one of the leading cause of female infertility. Here, we aimed to investigate the association of single-nucleotide polymorphism of INS, INSR, IRS1, IRS2, PPAR-G and CAPN10 gene in the pathogenesis of PCOS. A hospital-based, observational case-control study was carried on 169 PCOS and 169 control women in the southern region of India. Genotype was carried out by real-time polymerase chain reaction. A chi-square (χ²) test was performed and the genotypes were verified to comply with the Hardy- Weinberg equilibrium. Odds ratio and 95% confidence interval were calculated to assess the relative risk. Comparison of clinical characteristics of women with PCOS and controls reveal an increase in body mass index (BMI), luteinizing hormone / follicle stimulating hormone (LH/FSH) ratio, glucose levels, insulin, testosterone, hirsutism and antral follicular count in PCOS women. The variant rs1801278 (P = 0.002; OR = 2.88; 95% CI = 1.43, 5.80) show an association with PCOS. In the genotypic (P = 0.0002) and allelic models (P = 0.000), significance persisted even after Bonferroni correction. The genotypes of SNPs strongly influence BMI, LH, LH/FSH ratio, ovarian volume and antral follicular count in PCOS women. The study results were suggestive of a positive association between Gly972Arg of IRS1 and PCOS in the south Indian population, while INS, IRS2, PPAR-G and CAPN10 failed to show any association with PCOS in our studied population. Further studies focussing the role of IRS1 are warranted to delineate its implication towards PCOS.

IRS1 and IRS2: molecular characterization, tissue expression and transcriptional regulation by insulin in yellow catfish Pelteobagrus fulvidraco

The insulin receptor substrate (IRS) proteins, in particular, IRS1 and IRS2, are the key downstream players of insulin signaling pathway and the regulation of lipid metabolism. In the present study, two genes of IRS (IRS1 and IRS2) were isolated and characterized from yellow catfish Pelteobagrus fulvidraco. Their molecular characterizations, tissue expressions, and transcriptional levels by insulin both in vivo and in vitro were determined. The validated complementary DNAs encoding for IRS1 and IRS2 were 3693 and 3177 bp in length, encoding proteins of 1230 and 1058 amino acid residues, respectively. Similarly to mammals, amino acid sequence alignment revealed that IRSs contained an N-terminal pleckstrin homology (PH) domain, a phosphotyrosine-binding (PTB) domain, and several C-terminal multiple sites of tyrosine phosphorylation. Both IRS1 and IRS2 were widely expressed across the ten tissues (liver, white muscle, spleen, brain, gill, mesenteric fat, anterior intestine, heart, mid-kidney, and ovary), but at the variable levels. Insulin injection at 1 μg/g in vivo significantly stimulated the messenger RNA (mRNA) expression of IRS2, but not IRS1 mRNA expression levels in the liver of yellow catfish after 48 h. In hepatocytes of yellow catfish, insulin incubation significantly stimulated the IRS1 (at a 1000 nM insulin group) and IRS2 (at both 100 and 1000 nM insulin groups) mRNA expressions, which indicated that IRS2 was more sensitive than IRS1 to insulin stimulation in the liver of yellow catfish, and IRS2 played a more important role in mediating insulin's effects on the liver metabolism. The present study serves to increase our understanding into the function of IRS in fish.

Roles of Oxidative Stress in Polycystic Ovary Syndrome and Cancers

Oxidative stress (OS) has received extensive attention in the last two decades, because of the discovery that abnormal oxidation status was related to patients with chronic diseases, such as diabetes, cardiovascular, polycystic ovary syndrome (PCOS), cancer, and neurological diseases. OS is considered as a potential inducing factor in the pathogenesis of PCOS, which is one of the most common complex endocrine disorders and a leading cause of female infertility, affecting 4%–12% of women in the world, as OS has close interactions with PCOS characteristics, just as insulin resistance (IR), hyperandrogenemia, and chronic inflammation. It has also been shown that DNA mutations and alterations induced by OS are involved in cancer pathogenesis, tumor cell survival, proliferation, invasion, angiogenesis, and so on. Furthermore, recent studies show that the females with PCOS are reported to have an increasing risk of cancers. As a result, the more serious OS in PCOS is regarded as an important potential incentive for the increasing risk of cancers, and this study aims to analyze the possibility and potential pathogenic mechanism of the above process, providing insightful thoughts and evidences for preventing cancer potentially caused by PCOS in clinic.

FSH stimulates IRS-2 expression in human granulosa cells through cAMP/SP1, an inoperative FSH action in PCOS patients

Follicle stimulating hormone (FSH) plays a central role in growth and differentiation of ovarian follicles. A plethora of information exists on molecular aspects of FSH responses but little is known about the mechanisms involved in its cross-talk with insulin/IGF-1 pathways implicated in the coordination of energy homeostasis in preovulatory granulosa cells (GCs). In this study, we hypothesized that FSH may regulate IRS-2 expression and thereby maintain the energy balance in GCs. We demonstrate here that FSH specifically increases IRS-2 expression in human and rat GCs. FSH-stimulated IRS-2 expression was inhibited by actinomycin D or cycloheximide. Furthermore, FSH decreases IRS-2 mRNA degradation indicating post-transcriptional stabilization. Herein, we demonstrate a role of cAMP pathway in the activation of IRS-2 expression by FSH. Scan and activity analysis of IRS-2 promoter demonstrated that FSH regulates IRS-2 expression through SP1 binding sites. FSH stimulates SP1 translocation into nucleus and its binding to IRS-2 promoter. These results are corroborated by the fact that siRNA mediated knockdown of IRS-2 decreased the FSH-stimulated PI3K activity, p-Akt levels, GLUT4 translocation and glucose uptake. However, FSH was not able to increase IRS-2 expression in GCs from PCOS women undergoing IVF. Interestingly, IRS-2 mRNA expression was downregulated in GCs from the PCOS rat model. Taken together, our findings establish that FSH induces IRS-2 expression and thereby activates PI3K, Akt and glucose uptake. Crucially, our data confirms a molecular defect in FSH action in PCOS GCs which may cause deceleration of metabolism and follicular growth leading to infertility. These results lend support for a therapeutic potential of IRS-2 in the management of PCOS.

Identification of differentially expressed microRNAs in the ovary of polycystic ovary syndrome with hyperandrogenism and insulin resistance

BACKGROUND

Polycystic ovary syndrome (PCOS) is the commonest endocrinopathy in women of reproductive age. The patients often develop insulin resistance (IR) or hyperinsulinemia despite manifesting anovulation and signs of hyperandrogenism. The cause and effect relationship of hyperinsulinemia and hyperandrogenemia (HA) is still debated. Micro-ribonucleic acids (miRNAs) have recently been shown to play a role in regulation of ovarian function. Our current study focused on the altered expression of miRNAs with PCOS.

METHODS

Ovarian theca interna tissues were obtained from 10 PCOS patients and 8 controls that were non-PCOS and had normal insulin sensitivity undergoing laparoscopy and/or ovarian wedge resection. Total RNA of all samples was extracted. We studied the repertoire of miRNAs in both PCOS and non-PCOS women by microarray hybridization. Bioinformatic analysis was performed for predicting targets of the differentially expressed miRNAs. Furthermore, selected miRNAs were validated by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR).

RESULTS

A total of 27 miRNAs were differentially expressed in PCOS patients with respect to the controls in our discovery evaluationand two (miR-92a and miR-92b) of them were significantly downregulated in PCOS women in followed validation (P < 0.05). Targets prediction revealed that miR-92a targeted both GATA family of zinc finger transcription factor GATA-binding factor 6 (GATA6) and insulin receptor substrate proteins 2 (IRS-2).

CONCLUSIONS

MiRNAs are differentially expressed between PCOS patients and controls. We identified and validated two miRNAs-miR-92a and miR-92b. They are significantly downregulated and may be involved in the pathogenesis of PCOS.

Cryptotanshinone reverses ovarian insulin resistance in mice through activation of insulin signaling and the regulation of glucose transporters and hormone synthesizing enzymes

OBJECTIVE

To investigate the effects of cryptotanshinone (CRY), an active component of Chinese medicine, on ovarian androgen production, insulin resistance (IR), and glucose metabolism in mice.

DESIGN

Animal model and in vitro tissue model.

SETTING

University-affiliated laboratory.

ANIMAL(S)

Mice.

INTERVENTION(S)

Ovarian IR was induced by dexamethasone (DEX) in vivo. Animals were randomized to receive CRY treatment for 3 days or not. Ovulation rates, serum steroid levels, and glucose uptake in ovaries were quantified, and proteins in the phosphatidylinositol 3-hydroxy kinase pathway were measured. In vitro ovarian IR was also induced by DEX for 3 days. Ovarian steroid hormone secretion and glucose uptake were measured, and the hormone-synthesizing enzymes were determined by semiquantitative reverse transcription-polymerase chain reaction.

MAIN OUTCOME MEASURE(S)

Ovarian glucose uptake, in vivo ovulation rate, serum and culture medium steroid level, and molecular expression of phosphatidylinositol 3-hydroxy kinase and steroidogenic enzymes.

RESULT(S)

Dexamethasone significantly increased ovulation rates in vivo and increased T and E2 production and decreased ovarian glucose uptake in vivo and in vitro. Cryptotanshinone significantly reduced ovulation rates in vivo and decreased T and estrogen production in vitro. Cryptotanshinone attenuated the inhibition of DEX on AKT2 and suppressed the up-regulation of CYP11 and CYP17 expression by DEX.

CONCLUSION(S)

Cryptotanshinone reversed DEX-induced androgen excess and ovarian IR in mice through activation of insulin signaling and the regulation of glucose transporters and hormone-synthesizing enzymes. This suggests a potential role for CRY in treating the ovulatory dysfunction associated with PCOS.

The effect of short-term nutritional supplementation of ewes with lupin grain (Lupinus luteus) on folliculogenesis, the concentrations of hormones and glucose in plasma and follicular fluid and the follicular levels of P450 aromatase and IRS-1, -2 and -4

An experiment was conducted on 48 ewes during follicular and luteal phases of the oestrous cycle to determine the effect of a 5-day lupin grain supplementation (500 g/day) on folliculogenesis, plasma concentrations of glucose, insulin, FSH and oestradiol-17β (E2), follicular fluid concentrations of glucose, E2, androstenedione and progesterone and the levels of P450aromatase and insulin receptor substrate 1 (IRS-1), -2 and -4 in theca and granulosa cells. Average weight did not differ between lupin-fed and control groups. The numbers of follicles were increased (P<0.05; χ2) in the lupin-fed group. The plasma concentrations of glucose (P<0.05; ANOVA) and insulin (P<0.001; ANOVA) were higher in lupin-fed ewes. The plasma concentrations of FSH were not different but those of E2were decreased (P<0.001) in the lupin-fed group. Both the follicular fluid concentration of E2(P<0.05) and the level of P450aromatase in granulosa cells (P<0.05; ANOVA) were decreased in the lupin-fed group, but only during the follicular phase. The level of P450aromatase in granulosa cells was positively correlated with the concentration of E2in follicular fluid (r=0.820;P<0.001; ANOVA). The levels of IRS-1 and -2 in theca and granulosa cell lysates were increased in the lupin-fed group. These data suggest that insulin has a local role in the control of folliculogenesis and is likely to be a mediator of the effects of dietary energy intake on ovulation rate. We suggest that insulin acting through IRS proteins mediates the reproductive actions of insulin in the follicle and that IRS-1 and -2 are nutritionally regulated mediators of the action of insulin in the follicle.

The infusion of glucose in ewes during the luteal phase increases the number of follicles but reduces oestradiol production and some correlates of metabolic function in the large follicles

Short-term nutritional supplementation stimulates folliculogenesis in ewes probably by insulin-mediated actions of glucose in the follicle. The aim of this study was to determine the effect of glucose on follicle number and granulosa levels of Aromatase P450 and phosphorylated Akt and AMPK. Twelve Ile-de-France ewes were allocated to two groups; one (n=7) infused with saline and the other (n=5) with glucose (10mM/h) for 72h in the luteal phase. At the end of infusion, ovaries were collected and all follicles >1mm in diameter were dissected to recover granulosa cells. Aromatase P450 and phosphorylated Akt and AMPK were analysed by Western blotting of granulosa cell lysates. Blood plasmas collected before and during the infusions were analysed for progesterone, oestradiol, LH, FSH, glucose, insulin and IGF-I. The infusion of glucose significantly increased follicle number but, significantly reduced Aromatase P450 and phosphorylated Akt and AMPK in granulosa cells. The circulating concentration of glucose rose significantly 3h after the start of the glucose infusion and remained elevated until 27h then fell; the circulating concentration of insulin rose significantly by 3h and remained elevated. The circulating concentration of oestradiol fell significantly by 32h and remained low; the circulating concentrations of LH and FSH were unaffected. These data show that short-term infusion of glucose stimulated follicular growth but decreased Aromatase P450 in granulosa cells. The reduced levels of phosphorylated Akt and AMPK suggest that the phosphatidylinositol 3-kinase pathway has been inhibited by high concentrations of glucose. These data also suggest that there may be functional cross-talk between FSH and insulin signalling in granulosa cells.

Insulin increases de novo steroidogenesis in prostate cancer cells

Androgen-dependent pathways regulate maintenance and growth of normal and malignant prostate tissues. Androgen deprivation therapy (ADT) exploits this dependence and is used to treat metastatic prostate cancer; however, regression initially seen with ADT gives way to development of incurable castration-resistant prostate cancer (CRPC). Although ADT generates a therapeutic response, it is also associated with a pattern of metabolic alterations consistent with metabolic syndrome including elevated circulating insulin. Because CRPC cells are capable of synthesizing androgens de novo, we hypothesized that insulin may also influence steroidogenesis in CRPC. In this study, we examined this hypothesis by evaluating the effect of insulin on steroid synthesis in prostate cancer cell lines. Treatment with 10 nmol/L insulin increased mRNA and protein expression of steroidogenesis enzymes and upregulated the insulin receptor substrate insulin receptor substrate 2 (IRS-2). Similarly, insulin treatment upregulated intracellular testosterone levels and secreted androgens, with the concentrations of steroids observed similar to the levels reported in prostate cancer patients. With similar potency to dihydrotestosterone, insulin treatment resulted in increased mRNA expression of prostate-specific antigen. CRPC progression also correlated with increased expression of IRS-2 and insulin receptor in vivo. Taken together, our findings support the hypothesis that the elevated insulin levels associated with therapeutic castration may exacerbate progression of prostate cancer to incurable CRPC in part by enhancing steroidogenesis.

Cryptotanshinone reverses reproductive and metabolic disturbances in prenatally androgenized rats via regulation of ovarian signaling mechanisms and androgen synthesis

This trial explores 1) prenatally androgenized (PNA) rats as a model of polycystic ovary syndrome (PCOS) and 2) reproductive and metabolic effects of cryptotanshinone in PNA ovaries. On days 16-18 of pregnancy, 10 rats were injected with testosterone propionate (PNA mothers) and 10 with sesame oil (control mothers). At age 3 mo, 12 female offspring from each group were randomly assigned to receive saline and 12 cryptotanshinone treatment during 2 wk. Before treatment, compared with the 24 controls, the 24 PNA rats had 1) disrupted estrous cycles, 2) higher 17-hydroxyprogesterone (P = 0.030), androstenedione (P = 0.016), testosterone and insulin (P values = 0.000), and glucose (P = 0.047) levels, and 3) higher areas under the curve (AUC) for glucose (AUC-Glu, P = 0.025) and homeostatic model assessment for insulin resistance (HOMA-IR, P = 0.008). After treatment, compared with vehicle-treated PNA rats, cryptotanshinone-treated PNA rats had 1) improved estrous cycles (P = 0.045), 2) reduced 17-hydroxyprogesterone (P = 0.041), androstenedione (P = 0.038), testosterone (P = 0.003), glucose (P = 0.036), and insulin (P = 0.041) levels, and 3) lower AUC-Glu (P = 0.045) and HOMA-IR (P = 0.024). Western blot showed that cryptotanshinone reversed the altered protein expressions of insulin receptor substrate-1 and -2, phosphatidylinositol 3-kinase p85α, glucose transporter-4, ERK-1, and 17α-hydroxylase within PNA ovaries. We conclude that PNA model rats exhibit reproductive and metabolic phenotypes of human PCOS and that regulation of key molecules in insulin signaling and androgen synthesis within PNA ovaries may explain cryptotanshinone's therapeutic effects.

Berberine reduces insulin resistance induced by dexamethasone in theca cells in vitro

Theca cells with dexamethasone-induced insulin resistance showed defective glucose uptake and excessive testosterone production, both of which were effectively antagonized by berberine. Therefore, insulin-resistant theca cells may contribute to the pathogenesis of hyperandrogenism in polycystic ovary syndrome.

Study of association of IRS-1 and IRS-2 genes polymorphisms with clinical and metabolic features in women with polycystic ovary syndrome. Is there an impact?

OBJECTIVE

Insulin receptor substrate (IRS) proteins are critical to signal transduction in insulin target tissues. The present study was undertaken to determine whether IRS-1 Gly972Arg and IRS-2 Gly1057Asp influence hormonal and metabolic characteristics in Greek patients with polycystic ovary syndrome (PCOS) and controls.

MATERIAL AND METHODS

One hundred and eighty-three women with PCOS and 88 healthy volunteers were enrolled. Venous blood samples were obtained for genetic study and hormonal profile, glucose, and insulin assays, on days 3 to 7 from cycling patients. DNA was extracted by whole blood samples for genotyping and detection of IRS-1 Gly972Arg and IRS-2 Gly1057Asp polymorphisms.

RESULTS

Fifty-six women with PCOS (30.60%), whereas 12 women in the control group (13.64%) carried the IRS-1 polymorphism (p = 0.0026). No statistically significant differences in genotypes or allele frequencies for IRS-2 polymorphism were observed between controls and PCOS women. No significant differences in any clinical or hormonal measures between subjects on the basis of genotype were observed, except the increased levels of fasting glucose that exhibit the carriers of the Asp allele of the IRS-2 polymorphism.

CONCLUSIONS

Only the IRS-1 polymorphism is associated with increased susceptibility to PCOS in a Greek population. These loci should not be considered as major contributors to the hormonal and metabolic phenotype of PCOS.

Polymorphisms of the insulin receptor and the insulin receptor substrates genes in polycystic ovary syndrome: a Mendelian randomization meta-analysis

Polycystic ovary syndrome (PCOS) is a heterogeneous condition with unknown aetiology which is considered to be the most common endocrine disorder in women of reproductive age. In this work we investigated the association of insulin receptor (IotaNSR) and insulin receptor substrates (IRSs) polymorphisms with the risk of developing PCOS. The meta-analysis of eleven studies (889 cases, 1303 controls) yielded a significant association for IRS-1 Gly972Arg (G972R) polymorphism concerning the GR vs. GG genotype (OR: 1.77, 95% CI: 1.28, 2.45), with no between-studies heterogeneity. Concerning IotaNSR His1058 C/T, the meta-analysis of eight studies (795 cases, 576 controls) found no significant evidence for association with PCOS (OR for the TT+CT vs. CC comparison equal to 1.28 with 95% CI: 0.88, 1.85) and a moderate between studies variability (I(2)=44.6%). No evidence for publication bias was found in these meta-analyses. Following a multivariate Mendelian randomization approach, the overall OR was unaffected but the overall mean difference of fasting insulin levels between carriers of GR and RR genotypes in controls was significant (2.18, 95% CI: 0.36, 4.01). These results suggest that IRS-1 Gly972Arg polymorphism is significantly associated with the risk of developing PCOS and that this association is primarily mediated by increasing the levels of fasting insulin. The particular polymorphism is located in a region nearby two phosphorylation sites that interact physically with INSR and PI 3-kinase and there is enough evidence from the literature suggesting that the Arg972 variant is associated with decreased PI 3-kinase activity and impaired insulin-stimulated signaling.

Effects of testosterone and metformin on glucose metabolism in endometrium

OBJECTIVE

To investigate the effects of testosterone and metformin on glucose metabolism in endometrium.

DESIGN

In vitro experiment.

SETTING

Reproductive and Genetic Center, Obstetrics and Gynecology, The First Hospital of Peking University, Beijing, China.

PATIENT(S)

Premenopausal women undergoing total abdominal hysterectomy for uterine myoma or adenomyosis.

INTERVENTION(S)

Endometrial glandular epithelial cell culture.

MAIN OUTCOME MEASURE(S)

Insulin receptor substrate-1 (IRS-1) and glucose transporter 4 (GLUT-4) expression in endometrial glandular epithelial cell.

RESULT(S)

After the action of testosterone solution, the protein expressions of IRS-1mRNA, IRS-1, and GLUT-4 in endometrial glandular epithelial cells all decreased significantly. Metformin may reverse this effect.

CONCLUSION(S)

The high androgen levels in patients with polycystic ovary syndrome could induce insulin resistance in endometrial glandular epithelial cell, whereas metformin has an antagonizing effect.

Insulin receptor substrates (IRSs) and breast tumorigenesis

Insulin receptor substrate (IRS)-1 and IRS-2 are adaptor proteins in the insulin-like growth factor I (IGF-I)/IGF-I receptor (IGF-IR) pathway that mediate cell proliferation, migration, and survival. In addition to their role as scaffolding proteins in the cytoplasm, they are able to translocate into the nucleus and regulate gene transcription. IRS levels are developmentally and hormonally regulated in the normal mammary gland and both are essential for normal mammary gland bud formation and lactation. Both IRS-1 and IRS-2 are transforming oncogenes, and induce transformation and metastasis in vitro and in vivo. In breast cancer IRSs have unique functions, with IRS-1 being mainly involved in cell proliferation and survival, whereas IRS-2 has clear roles in cell migration and metastasis. In this review we will discuss the roles of IRSs in mammary gland development and breast cancer.

Diabetes, metabolic syndrome, and breast cancer: a review of the current evidence

Incidences of breast cancer, type 2 diabetes, and metabolic syndrome have increased over the past decades with the obesity epidemic, especially in industrialized countries. Insulin resistance, hyperinsulinemia, and changes in the signaling of growth hormones and steroid hormones associated with diabetes may affect the risk of breast cancer. We reviewed epidemiologic studies of the association between type 2 diabetes and risk of breast cancer and the available evidence on the role of hormonal mediators of an association between diabetes and breast cancer. The combined evidence supports a modest association between type 2 diabetes and the risk of breast cancer, which appears to be more consistent among postmenopausal than among premenopausal women. Despite many proposed potential pathways, the mechanisms underlying an association between diabetes and breast cancer risk remain unclear, particularly because the 2 diseases share several risk factors, including obesity, a sedentary lifestyle, and possibly intake of saturated fat and refined carbohydrates, that may confound this association. Although the metabolic syndrome is closely related to diabetes and embraces additional components that might influence breast cancer risk, the role of the metabolic syndrome in breast carcinogenesis has not been studied and thus remains unknown.

Polymorphism in HSD17B6 is associated with key features of polycystic ovary syndrome

OBJECTIVE

To investigate polymorphisms in androgen metabolism regulators that are implicated in the etiology of polycystic ovary syndrome (PCOS) in vitro; to investigate HSD17B6 and GATA6 to determine whether these genes are associated with susceptibility to PCOS or key phenotypic features of patients with PCOS.

DESIGN

Case-control association study.

SETTING

Participants with PCOS were recruited from a clinical-practice database, and controls, from the general community.

PATIENT(S)

One hundred seventy-three patients with PCOS and who were of Caucasian descent and conformed to the National Institutes of Health (NIH) diagnostic criteria; 107 normally ovulating women of Caucasian descent from the general community.

INTERVENTION(S)

Drawing of blood for DNA extraction.

MAIN OUTCOME MEASURE(S)

Frequency of HSD17B6 and GATA6 polymorphisms in cases and controls. Association of single-nucleotide polymorphisms from HSD17B6 in subjects with PCOS with key phenotypes of PCOS: androgen status, insulin resistance, and body mass index.

RESULT(S)

Allele distribution for the single-nucleotide polymorphism rs898611 in HSD17B6 was significantly different between PCOS and control subjects (P=.03). Presence of the polymorphic allele was associated with reduced fasting glucose-insulin ratio (P=.02) and increased homeostasis model assessment (P<.01) and body mass index (P<.001) as well as with reduced T (P=.03) in the PCOS group. No association was seen between GATA6 and any of the variables studied.

CONCLUSION(S)

These data suggest that polymorphisms in the HSD17B6 gene are associated with PCOS and key clinical phenotypes of the disorder.

Human ovarian theca cells in culture

Elucidating the regulation of androgen biosynthesis in ovarian theca cells is not only important for determining the mechanisms of regulation of estrogen biosynthesis throughout the menstrual cycle, but is also essential for understanding the pathogenesis of excess androgen biosynthesis and polycystic ovary syndrome (PCOS). Human theca cells in primary and long-term culture have provided model systems for examining theca cell differentiation as well as the mechanisms underlying basal and cAMP-regulated steroid biosynthesis at both the transcriptional and post-transcriptional level in normal and PCOS ovaries. Results of these studies are expected to lead to the identification of novel targets for clinical treatment of infertility and PCOS.

Dihydrotestosterone inhibits insulin-stimulated cyclin D2 messenger ribonucleic acid expression in rat ovarian granulosa cells by reducing the phosphorylation of insulin receptor substrate-1

The effect of 5alpha-dihydrotestosterone (DHT) on insulin-stimulated granulosa cell proliferation was examined using cyclin D2 mRNA as a marker. Granulosa cells from 3-d estradiol-treated immature rats showed a concentration-dependent increase in cyclin D2 mRNA expression in response to insulin. Exposure to DHT reduced the insulin-stimulated cyclin D2 mRNA expression. Inhibition of the two insulin-signaling pathways, ERK and phosphatidylinositol 3 kinase (PI3 kinase), by using specific inhibitors, also reduced this insulin-stimulated response. These results suggest that both ERK and PI3 kinase signaling are involved in insulin stimulated granulosa cell proliferation. DHT exposure resulted in reduced insulin-stimulated ERK phosphorylation. DHT treatment also reduced the insulin mediated insulin receptor substrate-1 and Raf-1 phosphorylation, the upstream molecules of ERK in insulin signaling pathway. Additionally, inhibition of insulin stimulated PI3 kinase activation reduced ERK phosphorylation. The present study therefore shows that the inhibitory effect of DHT on insulin-stimulated granulosa cell proliferation occurs early in the signaling pathway at the level of insulin receptor substrate-1 phosphorylation, leading to reduced ERK phosphorylation and subsequent inhibition of cyclin D2 mRNA expression.

Polymorphisms in the insulin receptor substrate-1 (IRS-1) gene and the insulin receptor substrate-2 (IRS-2) gene influence glucose homeostasis and body mass index in women with polycystic ovary syndrome and non-hyperandrogenic controls

BACKGROUND

We aimed to evaluate the influence of the Gly972Arg variant of the insulin receptor substrate-1 gene (IRS-1) and the Gly1057Asp variant in IRS-2 on insulin resistance and glucose tolerance in women with polycystic ovary syndrome (PCOS) and healthy controls.

METHODS

Genotypes, allelic frequencies, indexes of insulin resistance, glucose tolerance and hormone profiles were studied in a large sample of Spanish PCOS (n = 103) women compared with a control group (n = 48) of healthy women matched for body mass index.

RESULTS

No differences in genotype or allelic frequencies were found between PCOS patients and healthy controls. When considering control subjects and PCOS patients as a whole, IRS-1 Arg972 carriers also presented with increased fasting insulin (133 +/- 60 versus 95 +/- 67 pmol/l, P = 0.008) and insulin resistance measured by homeostasis model assessment (4.3 +/- 2.1 versus 3.1 +/- 2.4, P = 0.009) compared with subjects homozygous for Gly972 alleles. These differences were even higher when restricting the analysis to PCOS patients. Subjects homozygous for the Gly1057 allele of IRS-2 presented with increased 60 and 90 min oral glucose tolerance test (OGTT) glucose levels compared with carriers of one or two Asp1057 alleles (7.9 +/- 2.1 versus 7.1 +/- 2.1 mmol/l, P = 0.042 and 7.0 +/- 2.1 versus 6.0 +/- 1.8 mmol/l, P = 0.014), and a similar tendency was observed for 120 min OGTT glucose levels.

CONCLUSIONS

The Gly972Arg in IRS-1 and Gly1057Asp in IRS-2 polymorphisms influence glucose homeostasis in premenopausal women, but are not associated with PCOS.

Genetic contributions to glucose intolerance in polycystic ovary syndrome

Women with polycystic ovary syndrome (PCOS) are predisposed to develop impaired glucose tolerance and type-2 diabetes mellitus. Genetic factors appear to contribute to the insulin resistance that is characteristic of PCOS as well as to the failure of the pancreatic beta-cell to compensate adequately for this insulin resistance. The cumulative results of studies examining the genetic contribution to both the reproductive and metabolic phenotypes of PCOS are consistent with PCOS as a complex, polygenic disorder. This article reviews the background and recent studies examining the genetic contributions to glucose intolerance in PCOS.

Insulin-lowering agents in the management of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a medical condition that has brought multiple specialists together. Gynecologists, endocrinologists, cardiologists, pediatricians, and dermatologists are all concerned with PCOS patients and share research data and design clinical trials to learn more about the syndrome. Insulin resistance is a common feature of PCOS and is more marked in obese women, suggesting that PCOS and obesity have a synergistic effect on the magnitude of the insulin disorder. Hyperinsulinemia associated with insulin resistance has been causally linked to all features of the syndrome, such as hyperandrogenism, reproductive disorders, acne, hirsutism, and metabolic disturbances. Women with PCOS should be evaluated for cardiovascular risk factors, such as lipid profile and blood pressure. Modification of diet and lifestyle should be suggested to those who are obese. Several insulin-lowering agents have been tested in the management of PCOS. In particular, metformin is the only drug currently in widespread clinical use for treatment of PCOS. In a high percentage of patients, treatment with metformin is followed by regularization of menstrual cycle, reduction in hyperandrogenism and in cardiovascular risk factors, and improvement in response to therapies for induction of ovulation.

Selective ovary resistance to insulin signaling in women with polycystic ovary syndrome

OBJECTIVE

Insulin resistance is a common feature of both polycystic ovary syndrome (PCOS) and non-insulin-dependent diabetes mellitus (NIDDM); however, the persistent reproductive disturbances appear to be limited to the former, suggesting that insulin resistance in the ovary itself may confer this susceptibility.

DESIGN

Prospective study.

SETTING

University-affiliated department.

PATIENT(S)

Forty-four women undergoing IVF treatment, of whom 11 had polycystic ovaries and 33 had normal ovulation (NO).

INTERVENTION(S)

The various effects and signaling of insulin and insulin-like growth factor-1 (IGF-1) were examined in cultured ovarian granulosa cells treated with troglitazone (1 microg/mL) or with vehicle by reverse transcription-polymerase chain reaction, western blot, and in vitro functional analyses.

MAIN OUTCOME MEASURE(S)

Glycogen and DNA syntheses, mRNA and protein expression, and cellular localization of insulin/IGF-1 receptors and insulin receptor substrates (IRSs).

RESULT(S)

There were significant decreases in insulin-stimulated glucose incorporation into glycogen in PCOS cells, which is a metabolic action of insulin. However, IGF-1 stimulation was found to be greater in PCOS cells at all experimental concentrations with respect to thymidine incorporation compared with NO cells, which is a mitogenic action. Troglitazone increased the insulin-induced glycogen synthesis but reduced the IGF-1-augmented responses of DNA synthesis in PCOS cells to the range within those of NO granulosa cells. We then found that troglitazone treatment reversed the expression imbalance between IRS-1 and IRS-2 in PCOS cells.

CONCLUSION(S)

There is a selective defect in insulin actions in PCOS granulosa cells, which suggests ovarian insulin resistance, and this metabolic phenotype is associated with an enhanced IGF-1 mitogenic potential. Troglitazone could divergently alter expression of various IRS molecules and insulin actions and could be used as an ovarian insulin sensitizer and mitogen/steroidogenic inhibitor in PCOS.

Impaired ('diabetic') insulin signaling and action occur in fat cells long before glucose intolerance--is insulin resistance initiated in the adipose tissue?

This review postulates and presents recent evidence that insulin resistance is initiated in the adipose tissue and also suggests that the adipose tissue may play a pivotal role in the induction of insulin resistance in the muscles and the liver. Marked impairments in insulin's intracellular signaling cascade are present in fat cells from type 2 diabetic patients, including reduced IRS-1 gene and protein expression, impaired insulin-stimulated PI3-kinase and PKB/Akt activities. In contrast, upstream insulin signaling in skeletal muscle from diabetic subjects only shows modest impairments and PKB/Akt activation in vivo by insulin appears normal. However, insulin-stimulated glucose transport and glycogen synthesis are markedly reduced. Similar marked impairments in insulin signaling, including reduced IRS-1 expression, impaired insulin-stimulated PI3-kinase and PKB/Akt activities are also seen in some (approximately 30%) normoglycemic individuals with genetic predisposition for type 2 diabetes. In addition, GLUT4 expression is markedly reduced in these cells, similar to what is seen in diabetic cells. The individuals with reduced cellular expression of IRS-1 and GLUT4 are also markedly insulin resistant and exhibit several characteristics of the Insulin Resistance Syndrome.Thus, a 'diabetic' pattern is seen in the fat cells also in normoglycemic subjects and this is associated with a marked insulin resistance in vivo. It is proposed that insulin resistance and/or its effectors is initiated in fat cells and that this may secondarily encompass other target tissues for insulin, including the impaired glucose transport in the muscles.

Distinct and overlapping functions of insulin and IGF-I receptors

Targeted gene mutations have established distinct, yet overlapping, developmental roles for receptors of the insulin/IGF family. IGF-I receptor mediates IGF-I and IGF-II action on prenatal growth and IGF-I action on postnatal growth. Insulin receptor mediates prenatal growth in response to IGF-II and postnatal metabolism in response to insulin. In rodents, unlike humans, insulin does not participate in embryonic growth until late gestation. The ability of the insulin receptor to act as a bona fide IGF-II-dependent growth promoter is underscored by its rescue of double knockout Igf1r/Igf2r mice. Thus, IGF-II is a true bifunctional ligand that is able to stimulate both insulin and IGF-I receptor signaling, although with different potencies. In contrast, the IGF-II/cation-independent mannose-6-phosphate receptor regulates IGF-II clearance. The growth retardation of mice lacking IGF-I and/or insulin receptors is due to reduced cell number, resulting from decreased proliferation. Evidence from genetically engineered mice does not support the view that insulin and IGF receptors promote cellular differentiation in vivo or that they are required for early embryonic development. The phenotypes of insulin receptor gene mutations in humans and in mice indicate important differences between the developmental roles of insulin and its receptor in the two species.

Defects of the insulin receptor substrate (IRS) system in human metabolic disorders

Insulin receptor substrate (IRS) molecules are key mediators in insulin signaling and play a central role in maintaining basic cellular functions such as growth, survival, and metabolism. They act as docking proteins between the insulin receptor and a complex network of intracellular signaling molecules containing Src homology 2 (SH2) domains. Four members (IRS-1, IRS-2, IRS-3, IRS-4) of this family have been identified that differ as to tissue distribution, subcellular localization, developmental expression, binding to the insulin receptor, and interaction with SH2 domain-containing proteins. Results from targeted disruption of the IRS genes in mice have provided important clues to the functional differences among these related molecules, suggesting they play different and specific roles in vivo. The available data are consistent with the notion that IRS-1 and IRS-2 are not functionally interchangeable in tissues that are responsible for glucose production (liver), glucose uptake (skeletal muscle and adipose tissue), and insulin production (pancreatic beta cells). In fact, IRS-1 appears to have its major role in skeletal muscle whereas IRS-2 appears to regulate hepatic insulin action as well as pancreatic beta cell development and survival. By contrast, IRS-3 and IRS-4 genes appear to play a redundant role in the IRS signaling system. Defects in muscle IRS-1 expression and function have been reported in insulin-resistant states such as obesity and type 2 diabetes. Several polymorphisms in the IRS genes have been identified, but only the Gly-->Arg972 substitution of IRS-1, interacting with environmental factors, seems to have a pathogenic role in the development of type 2 diabetes. In contrast, polymorphisms of the other IRS genes do not appear to contribute to type 2 diabetes.

[The ovary and insulin resistance]

Insulin resistance appears to be responsible of approximately half of the cases of polycystic ovaries, the other half being probably provoked by an anomaly of the stimulation of ovaries by an excess of LH. Nevertheless, it is likely that in most cases the two factors conjugate. The excess of androgen production by the ovarian stroma is one of the major symptoms of this disease. Today, however, the diagnosis is carried mainly with the assistance of ultra-sounds which, besides the increased ovarian volume, have permitted to discover an increased ovarian stromal vascularity. Two essential datas derive from the whole works: the increased frequency of ovarian hyperstimulation syndrome and the great number of metabolic complications which requires an endocrinological supervision. But the most recent works focus on the extension to all ages of this form of pathology: from the intra-uterine life to the post menopause; and on the hereditary character of this disease. The mystery remains concerning the mechanism of the favourable effect in clomifene resistant PCOS, of surgical and laparoscopic methods of ovulation induction to which it may be useful to resort after mature consideration. More recently the benefit at the administration of metformine has been confirmed by several works.