Adiposity associated rise in leptin impairs ovarian activity during winter dormancy in Vespertilionid bat, Scotophilus heathi

Day-night and seasonal variation of human gene expression across tissues

Circadian and circannual cycles trigger physiological changes whose reflection on human transcriptomes remains largely uncharted. We used the time and season of death of 932 individuals from GTEx to jointly investigate transcriptomic changes associated with those cycles across multiple tissues. Overall, most variation across tissues during day-night and among seasons was unique to each cycle. Although all tissues remodeled their transcriptomes, brain and gonadal tissues exhibited the highest seasonality, whereas those in the thoracic cavity showed stronger day-night regulation. Core clock genes displayed marked day-night differences across multiple tissues, which were largely conserved in baboon and mouse, but adapted to their nocturnal or diurnal habits. Seasonal variation of expression affected multiple pathways, and it was enriched among genes associated with the immune response, consistent with the seasonality of viral infections. Furthermore, they unveiled cytoarchitectural changes in brain regions. Altogether, our results provide the first combined atlas of how transcriptomes from human tissues adapt to major cycling environmental conditions. This atlas may have multiple applications; for example, drug targets with day-night or seasonal variation in gene expression may benefit from temporally adjusted doses.

Insights into Interactions of Human Cytochrome P450 17A1: Review

Abstract:

Cytochrome P450s are a widespread and vast superfamily of hemeprotein monooxygenases that metabolize physiologically essential chemicals necessary for most species' survival, from protists to plants to humans. They catalyze the synthesis of steroid hormones, cholesterol, bile acids, and arachidonate metabolites and the degradation of endogenous compounds such as steroids, fatty acids, and other catabolizing compounds as an energy source and detoxifying xenobiotics such as drugs, procarcinogens, and carcinogens. The human CYP17A1 is one of the cytochrome P450 genes located at the 10q chromosome. The gene expression occurs in the adrenals and gonads, with minor amounts in the brain, placenta, and heart. This P450c17 cytochrome gene is a critical steroidogenesis regulator which performs two distinct activities: 17 alpha-hydroxylase activity (converting pregnenolone to 17-hydroxypregnenolone and progesterone to 17-hydroxyprogesterone, these precursors are further processed to provide glucocorticoids and sex hormones) and 17, 20-lyase activity (which converts 17-hydroxypregnenolone to DHEA). Dozens of mutations within CYP17A1 are found to cause 17-alpha-hydroxylase and 17, 20-lyase deficiency. This condition affects the function of certain hormone-producing glands, resulting in high blood pressure levels (hypertension), abnormal sexual development, and other deficiency diseases. This review highlights the changes in CYP17A1 associated with gene-gene interaction, drug-gene interaction, chemical-gene interaction, and its biochemical reactions; they have some insights to correlate with the fascinating functional characteristics of this human steroidogenic gene. The findings of our theoretical results will be helpful to further the design of specific inhibitors of CYP17A1.

Day-night and seasonal variation of human gene expression across tissues

Circadian and circannual cycles trigger physiological changes whose reflection on human transcriptomes remains largely uncharted. We used the time and season of death of 932 individuals from GTEx to jointly investigate transcriptomic changes associated with those cycles across multiple tissues. Overall, most variation across tissues during day-night and among seasons was unique to each cycle. Although all tissues remodeled their transcriptomes, brain and gonadal tissues exhibited the highest seasonality, whereas those in the thoracic cavity showed stronger day-night regulation. Core clock genes displayed marked day-night differences across multiple tissues, which were largely conserved in baboon and mouse, but adapted to their nocturnal or diurnal habits. Seasonal variation of expression affected multiple pathways and it was enriched among genes associated with the immune response, consistent with the seasonality of viral infections. Furthermore, they unveiled cytoarchitectural changes in brain regions. Altogether, our results provide the first combined atlas of how transcriptomes from human tissues adapt to major cycling environmental conditions.

Prolactin modulates luteal activity in the short-nosed fruit bat, Cynopterus sphinx during delayed embryonic development

The aim of this study was to evaluate the role of prolactin as a modulator of luteal steroidogenesis during the period of delayed embryonic development in Cynopterus sphinx. A marked decline in circulating prolactin levels was noted during the months of November through December coinciding with the period of decreased serum progesterone and delayed embryonic development. The seasonal changes in serum prolactin levels correlated positively with circulating progesterone (P) level, but inversely with circulating melatonin level during first pregnancy showing delayed development in Cynopterus sphinx. The results also showed decreased expression of prolactin receptor-short form (PRL-RS) both in the corpus luteum and in the utero-embryonic unit during the period of delayed embryonic development. Bats treated in vivo with prolactin during the period of delayed development showed significant increase in serum progesterone and estradiol levels together with significant increase in the expression of PRL-RS, luteinizing hormone receptor (LH-R), steroidogenic acute receptor protein (STAR) and 3β-hydroxysteroid dehydrogenase (3β-HSD) in the ovary. Prolactin stimulated ovarian angiogenesis (vascular endothelial growth factor) and cell survival (B-cell lymphoma 2) in vivo. Significant increases in ovarian progesterone production and the expression of prolactin-receptor, LH-R, STAR and 3β-HSD proteins were noted following the exposure of LH or prolactin in vitro during the delayed period. In conclusion, short-day associated increased melatonin level may be responsible for decreased prolactin release during November-December. The decline in prolactin level might play a role in suppressing P and estradiol-17β (E2) estradiol levels thereby causing delayed embryonic development in C. sphinx.

Anti-estrogenic effect of semicarbazide in female zebrafish (Danio rerio) and its potential mechanisms

Semicarbazide (SMC), a member of the hydrazine family, has various toxic effects and has been detected in organisms, aquatic environments, and food. SMC exposure inhibited the transcription of hepatic vitellogenin and estrogen receptors in female zebrafish (Danio rerio), suggesting that it had anti-estrogenic properties. In order to elucidate the mechanisms underlying these, we exposed female zebrafish to SMC and used enzyme-linked immunosorbent assays to examine plasma 17β-estradiol (E2) and testosterone (T) levels. Gonad histology was analyzed and the mRNA expression of genes involved in the reproductive axis, the gamma-aminobutyric acid (GABA) shunt, and leptin was quantified by real-time PCR. Zebrafish were exposed to 1, 10, 100, or 1000μg/L SMC in a semi-static system for 96hours or 28 days. Plasma E2 levels were significantly decreased and ovarian maturation was inhibited by SMC, suggesting that its anti-estrogenic effect was exerted by reducing endogenous E2 levels. This was likely due to the SMC-mediated inhibition of cytochrome P450 (CYP) 19A mRNA levels, because this enzyme catalyzes the conversion of T to E2 in the gonads. In addition, down-regulation of the mRNA expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase, steroidogenic acute regulatory protein, CYP17, and 17beta-hydroxysteroid dehydrogenase was observed; this was predicted to reduce T concentrations and further contribute to the reduced E2 levels. SMC-induced changes in the expression of these steroidogenic genes correlated with decreased transcription of gonadotropic hormones (follicle-stimulating hormone and luteinizing hormone) and significantly elevated leptin expression. Furthermore, SMC also altered expression of the key enzyme in gamma-aminobutyric acid (GABA) synthesis, GABA receptors, and salmon gonadotropin-releasing hormone, thus affecting gonadotropin expression. Overall, SMC acted at multiple sites related to reproduction to reduce plasma E2 levels, consequently exerting an anti-estrogenic effect in female zebrafish. These effects were observed at environmentally relevant concentrations and highlight the importance of controlling SMC contamination.

Regulation and mechanism of leptin on lipid metabolism in ovarian follicle cells from yellow catfish Pelteobagrus fulvidraco

The present study was conducted to determine the effect of leptin on lipid metabolism in ovarian follicle cells of yellow catfish Pelteobagrus fulvidraco. For that purpose, primary ovarian follicle cells were isolated from yellow catfish, cultured and subjected to different treatments (control, 0.1% DMSO, 500ng/ml leptin, 500ng/ml leptin plus 100μM wortmannin, 500ng/ml leptin plus 50nM AG490, respectively) for 48h. Intracellular triglyceride (TG) content, the activities (CPT I, FAS, G6PD, and 6PGD) and/or expression level of several enzymes (CPT I, FAS, G6PD, 6PGD, ACCa and ACCb), as well as the mRNA expression of transcription factors (PPARα, PPARγ and SREBP-1) involved in lipid metabolism were determined. Recombinant human leptin (rt-hLEP) incubation significantly reduced intracellular TG content, activities and mRNA levels of FAS, G6PD and 6PGD, SREBP-1 and PPARγ, but enhanced activity and mRNA level of CPT I, PPARα and ACCa. Specific inhibitors AG490 and wortmannin of JAK-STAT and IRS-PI3K signaling pathways prevented leptin-induced changes, indicating that JAK-STAT and IRS-PI3K signaling pathways were involved in the process of leptin-induced changes of lipid metabolism. Based on these observations above, for the first time, our study indicated that leptin reduced lipid deposition by activating lipolysis and suppressing lipogenesis in ovarian follicles of yellow catfish, and both JAK-STAT and IRS-PI3K signaling pathways were involved in the changes of leptin-induced lipid metabolism.

Localization of resistin and its possible roles in the ovary of a vespertilionid bat, Scotophilus heathi

The aim of the present study was to evaluate the expression and effect of resistin on ovarian activities of Scotophilus heathi. Immunohistochemical study showed marked variation in resistin immunostaining during different reproductive phases. Most intense immunostaining of resistin was noticed in thecal-interstitial cells in ovary during the period of delayed ovulation, the period of increased androgen synthesis and suppressed ovulation. The changes in ovarian resistin level also correlated positively with circulating leptin level and body white adipose tissue accumulation. The in vitro study showed that resistin alone preferentially stimulated progesterone synthesis, but with luteinizing hormone (LH) stimulated androgen secretion. Resistin alone dose-dependently increased expression of LH-receptor, steroidogenic acute regulatory protein and insulin receptor proteins in the ovary, whereas together with LH showed dose-dependent stimulatory effect on expression of androgen receptor and insulin receptor proteins in the ovary. In conclusion, during the period of fat accumulation increased ovarian resistin level may be responsible for increased androgen synthesis through insulin receptor mediated pathways in the ovary of S. heathi.

Effects of seasonal adiposity on ovarian activity of Vespertilionid bat, Scotophilus heathi: proteomics analysis

In present study comparative proteomics was utilized to identify ovarian protein profiles and correlate the expression of these proteins with adiposity induced changes in ovarian activity leading to suppression of ovulation (delayed ovulation) in the bat, S. heathi. To achieve this, two-dimension gel electrophoresis combined with protein identification by tandem mass spectrometry (LC-MS/MS) was applied. Protein profiles were obtained from intact ovaries of bats collected during recrudescence (basal body weight) and delayed ovulation (increased body weight) phases of reproductive cycle. Out of 42 differentially expressed protein spots, 15 protein spots were identified by LC-MS/MS. A majority of the 15 protein spots identified belonged to a group of enzymes within the glycolytic and citrate cycles. Greater concentrations of these enzymes were found during the period of delayed ovulation, which may be responsible for an increase in the production of ATP within the ovary. The increased metabolic activity and energy production observed within the ovary during winter dormancy may be required for increased steroidogenic activity during this period. The protein 14-3-3 identified by LC-MS/MS was verified by immunoblotting, which confirmed its increased expression during the period of delayed ovulation and may be associated with development of insulin resistance. Treatment with adipokines (adiponectin, resistin) is responsible for increased expression of 14-3-3 protein in the ovary of S. heathi. Adiposity-associated rise in adipokines are thus responsible for increased expression of 14-3-3 protein in the ovary of S. heathi, which may be responsible for prolonged survival of antral follicles and suppression of ovulation. The 14-3-3 protein may represent a new marker for adiposity associated ovarian anovulation (disorders).

Effects of resistin on ovarian folliculogenesis and steroidogenesis in the vespertilionid bat, Scotophilus heathi

The bat Scotophilus heathi exhibit prolonged anovulatory condition known as delayed ovulation coinciding with the period of extensive fat accumulation. The present study was undertaken to find out whether extensive accumulation of fat in S. heathi is responsible for suppression of ovarian activity by increasing production of adipokine resistin in the bat. This was achieved by (a) investigating variation in serum resistin level in relation to the changes in the body fat mass and (b) evaluating the effect of resistin treatment on ovarian activity with reference to steroid synthesis. An attempt was also made to determine whether resistin mediate its effects on ovary through signal transducer and activator of transcription 3 (STAT3) signaling mechanism. The results showed significant seasonal variation in serum resistin level with the peak level coinciding with the period of maximum fat accumulation, high circulating androgen level and period of anovulation. The treatment with resistin to the bat caused increase in androstenedione due to stimulatory effects on 3β-hydroxysteroid dehydrogenase, but decrease in estradiol level due to inhibitory effect on aromatase. Resistin treatment increased androgen receptor protein together with increased insulin receptor but not through conventional luteinizing hormone receptor and steroidogenic acute regulatory protein mediated pathways. This study further showed that resistin treatment increases androstenedione synthesis and up-regulates insulin receptor in the ovary through STAT3 mediated pathways. These findings suggest that obese women through increased resistin synthesis may causes development of non-ovulatory antral follicles through insulin receptor signaling cascade.

Modulation of ovarian steroidogenesis by adiponectin during delayed embryonic development of Cynopterus sphinx

The aim of present study was to evaluate role of adiponectin in ovarian steroidogenesis during delayed embryonic development of Cynopterus sphinx. This study showed significantly low circulating adiponectin level and a decline in expression of adiponectin receptor 1 (AdipoR1) in the ovary during the period of delayed embryonic development as compared with the normal development. The adiponectin treatment in vivo during the period of delayed development caused significantly increased in circulating progesterone and estradiol levels together with increased expression of AdipoR1 in the ovary. The in vitro study confirmed the stimulatory effect of adiponectin on progesterone synthesis. Both in vivo and in vitro studies showed that the effects of adiponectin on ovarian steroidogenesis were mediated through increased expression of luteinizing hormone-receptor, steroidogenic acute regulatory protein and 3β-hydroxyl steroid dehydrogenase enzyme. The adiponectin treatment may also promote progesterone synthesis by modulating ovarian angiogenesis, cell survival and rate of apoptosis.

Endocrine regulation of bone and energy metabolism in hibernating mammals

Precise coordination among organs is required to maintain homeostasis throughout hibernation. This is particularly true in balancing bone remodeling processes (bone formation and resorption) in hibernators experiencing nutritional deprivation and extreme physical inactivity, two factors normally leading to pronounced bone loss in non-hibernating mammals. In recent years, important relationships between bone, fat, reproductive, and brain tissues have come to light. These systems share interconnected regulatory mechanisms of energy metabolism that potentially protect the skeleton during hibernation. This review focuses on the endocrine and neuroendocrine regulation of bone/fat/energy metabolism in hibernators. Hibernators appear to have unique mechanisms that protect musculoskeletal tissues while catabolizing their abundant stores of fat. Furthermore, the bone remodeling processes that normally cause disuse-induced bone loss in non-hibernators are compared to bone remodeling processes in hibernators, and possible adaptations of the bone signaling pathways that protect the skeleton during hibernation are discussed. Understanding the biological mechanisms that allow hibernators to survive the prolonged disuse and fasting associated with extreme environmental challenges will provide critical information regarding the limit of convergence in mammalian systems and of skeletal plasticity, and may contribute valuable insight into the etiology and treatment of human diseases.

Seasonal variation of energy reserves and reproduction in neotropical free-tailed bats Molossus molossus (Chiroptera: Molossidae)

Seasonal variation is a key factor regulating energy metabolism and reproduction in several mammals, including bats. This study aimed to track seasonal changes in the energy reserves of the insectivorous bat Molossus molossus associated with its reproductive cycle. Adult males were collected during the four neotropical annual seasons in Viçosa - MG, Brazil. Blood and tissues were collected for metabolic analysis and testes were removed for histology and morphometry. Our results show that liver and breast muscle glycogen concentrations were significantly lower in winter. The adiposity index was significantly higher in the fall compared to winter and spring. Seminiferous tubules were greater in diameter in animals captured in fall and winter, indicating a higher investment in spermatic production during these seasons. The percentage of Leydig cells was higher in summer compared to fall and winter. We suggest that M. molossus presents a type of seasonal reproduction with two peaks of testicular activity: one in fall, with higher sperm production (spermatogenesis), and another in summer, with higher hormone production (steroidogenesis). The metabolic pattern may be associated with reproductive events, especially due to the highest fat storage observed in the fall, which coincides with the further development of the seminiferous tubules.

Effects of adiponectin on ovarian folliculogenesis and steroidogenesis in the vespertilionid bat, Scotophilus heathi

The bat Scotophilus heathi undergo anovulation, known as delayed ovulation, coinciding with the period of seasonal adiposity due to fat accumulation. Because adiponectin is a well known fat cell product, it might be responsible for adiposity related anovulation in S. heathi. The aim of this study was thus to evaluate the effects of adiponectin treatment on ovarian activity in S. heathi. The bat during the period of delayed ovulation was treated with adiponectin (25 μg/day) for 12 days. Changes taken place in the ovarian activity of the treated bat was compared with the control bat and results obtained are presented here. Adiponectin treatment significantly decreased body mass by depleting adipose tissue. It acts directly upon the ovary and promotes antral follicular development by stimulating cell proliferation and modulating ovarian steroidogenesis. The bat treated with adiponectin showed significant decrease in circulating androstenedione (A4) and estradiol (E2) levels, but increase in circulating progesterone (P4) level. The inhibitory effect of adiponectin on androgen synthesis may be due to decreased thecal-interstitial cells differentiation in stroma by suppressing adiponectin receptor type 1 (AdipoR1), luteinizing hormone (LH) and insulin receptors in the ovary of S. heathi. The study provides evidences suggesting that the adiponectin treatment suppresses adiposity and restores normal ovarian activity.

Leptin-mediated modulation of steroidogenic gene expression in hypoxic zebrafish embryos: implications for the disruption of sex steroids

Hypoxia can impair reproduction of fishes through the disruption of sex steroids. Here, using zebrafish (Danio rerio) embryos, we investigated (i) whether hypoxia can directly affect steroidogenesis independent of pituitary regulation via modulation of steroidogenic gene expression, and (ii) the role of leptin in hypoxia-induced disruption of steroidogenesis. Exposure of fertilized zebrafish embryos to hypoxia (1.0 mg O(2) L(-1)) from 0-72 h postfertilization (hpf), a developmental window when steroidogenesis is unregulated by pituitary influence, resulted in the up-regulation of cyp11a, cyp17, and 3β-hsd and the down-regulation of cyp19a. Similar gene expression patterns were observed for embryos exposed to 10 mM cobalt chloride (CoCl(2), a chemical inducer of hypoxia-inducible factor 1, HIF-1), suggesting a regulatory role of HIF-1 in steroidogenesis. Testosterone (T) and estradiol (E2) concentrations in hypoxic embryos were greater and lesser, respectively, relative to the normoxic control, thus leading to an increased T/E2 ratio. Expression of the leptin-a gene (zlep-a) was up-regulated upon both hypoxia and CoCl(2) treatments. Functional assays suggested that under hypoxia, elevated zlep-a expression might activate cyp11a and 3β-hsd and inhibit cyp19a. Overall, this study indicates that hypoxia, possibly via HIF-1-induced leptin expression, modulates sex steroid synthesis by acting directly on steroidogenic gene expression.

Localization of adiponectin and its receptor and its possible roles in the ovary of a vespertilionid bat, Scotophilus heathi

The aim of this study was to evaluate the seasonal variation in serum adiponectin levels and ovarian expression of adiponectin and its receptor in the Scotophilus heathi bat and their relationship to the changes in the body fat mass, serum insulin and luteinizing hormone (LH) levels, and ovarian activity. A very high level of circulating adiponectin was found during recrudescence, whereas a very low level of circulating adiponectin was observed during pre-ovulatory period. The increased circulating adiponectin level coincided with fat deposition, insulin resistance and hyperinsulinemia (HI) in S. heathi. Immunocytochemical study in the ovary of bat showed localization of adiponectin mainly in thecal-interstitial cells (TICs), and adiponectin receptor 1 (AdipoR1) in the granulosa cells of growing follicles, but showed no staining in atretic follicle. Seasonal changes in ovarian adiponectin and AdipoR1 levels showed two peaks (during recrudescence and ovulatory phases) coinciding with two periods of follicular development. Adiponectin in the absence of LH, as occur during recrudescence, stimulates androstenedione (A4) synthesis in vitro by up-regulating the insulin receptor (IR). Adiponectin in presence of LH, as occur during pre-ovulatory phase, inhibits A4 synthesis in vitro by down-regulating androgen receptor (AR). Further, the in vitro study showed that adiponectin, in presence of LH, also promotes luteinizing hormone receptor (LH-R) and steroidogenic acute regulatory protein (StAR) level in the ovary, which might help in development of ovulatory follicles. In brief, adiponectin in the absence of LH induces increased A4 synthesis and consequently the condition of delayed ovulation, whereas in the presence LH suppresses both synthesis and action of A4 and thus induces preovulatory condition in the ovary of S. heathi.

Regulation of leptin synthesis during adipogenesis in males of a vespertilionid bat, Scotophilus heathi

The aim of this study was to elucidate the hormonal regulation of leptin synthesis by the white adipose tissue (WAT) during the period of fat accumulation in male Scotophilus heathi. An in vivo study showed a significant correlation between the seasonal changes in serum insulin level with the circulating leptin level and with the changes in body fat mass in S. heathi. An in vitro study showed insulin induced a significant increase in expression of leptin protein in WAT. The insulin-stimulated increase in leptin expression was associated with increased uptake of glucose in the WAT. Two glucose transporters (GLUT4 and GLUT8) are utilized for transport of glucose in the WAT during adipogenesis in the bat. The bats showed high insulin and glucose levels, but a reduction in insulin receptor protein during the period of fat deposition, suggesting insulin resistance, which improved in late winter (January) when most of the fat has been utilized as a metabolic fuel. The in vitro study confirmed that insulin enhanced leptin and GLUT4 expression in WAT. The in vitro study further showed that the expression of leptin is directly proportional to the amount of glucose uptake by the WAT. The expression of GLUT4 and GLUT8 were also shown to be differentially regulated by insulin during adipogenesis. The insulin-stimulated increase in leptin synthesis by WAT is mediated through phosphorylation of MAPK in S. heathi. The specific role of GLUT4 and GLUT8 in the regulation of leptin synthesis during adipogenesis needs further investigation.

Effects of chronic bhang (cannabis) administration on the reproductive system of male mice

BACKGROUND

The purpose of this study was to investigate the effect of chronic uptake of bhang, prepared from the Cannabis sativa, on male reproductive physiology in adult male Parkes strain (P) mice. An attempt was also made to investigate the presence of cannabinoid 1 (CB1) and cannabinoid 2 (CB2) receptors, and fatty acid amide hydrolase (FAAH) in the testis and to evaluate any changes in it resulting from chronic intake of bhang in mice.

METHODS AND RESULTS

Adult male mice were given bhang (3 or 6 mg/kg body weight/day) orally for 36 consecutive days. Chronic intake of bhang caused regressive changes in the testes and suppressed sperm count, viability and motility. Bhang intake also caused significant decline in circulating testosterone level due to decline in testicular 3β HSD enzyme activity. An immunohistochemical study demonstrated the presence of CB1, CB2 and FAAH in the testis of mice. The present study also showed significant variation in the CB1 and CB2 receptors and FAAH protein levels in testes of mice exposed to bhang. These suppressive effects may be due to inhibitory effect of bhang on pituitary expression of gonadotrophin releasing hormone (GnRH) I receptor protein. Treatment of testes with bhang in vitro significantly decreased testicular luteinizing hormone receptor (LHR) and FAAH expression suggesting direct action of bhang on testicular activity.

CONCLUSIONS

The findings of this study thus suggest that bhang may impair fertility in male mice through alteration in the testicular endocannabinoid system and that chronic bhang exposure in humans would be predicted to alter male fertility.

Increased circulating leptin level inhibits folliculogenesis in vespertilionid bat, Scotophilus heathii

The present study investigates the mechanism by which obesity associated rise in leptin and insulin levels cause anovulation in vespertilionid bat, Scotophilus heathii. In the ovary of S. heathii, leptin and insulin receptors were mainly localized in interstitial and thecal cells and in the granulosa cells of primary follicles suggesting its possible role in androgen synthesis and follicular development. Adiposity associated increase in circulating leptin level down regulate ovarian LH-receptor expression and produce characteristic morphological changes in the antral follicles, such as hypertrophy of granulosa cells and a sharp decline in the rate of proliferation as well as apoptosis in the antral follicles. These follicles are referred as unique antral follicle. The in vitro study confirmed the in vivo findings that the high dose of leptin suppresses apoptosis and LH receptors. The present study thus showed that the adiposity associated increase in leptin during the first phase of follicular development inhibits folliculogenesis and simultaneously suppresses both follicular proliferation and apoptosis by reducing sensitivity to gonadotropin stimulation and decreasing circulating LH levels.

Structural and functional studies of leptins from hibernating and non-hibernating bats

Leptin, a 16-kDa hormone produced by mature adipocytes, has been shown to regulate the hibernation of mammals. In this study, the leptin gene sequences of both hibernating (Rhinolophus ferrumequinum) and non-hibernating (Rousettus leschenaultii) bats were determined, and the leptin proteins from these two different species of bats were expressed in Escherichia coli for the first time. Results showed that the amino acid sequence of the leptin protein from hibernating bats had a lower degree of identity than that from non-hibernating bats to those of several non-hibernating mammals. The leptin protein of hibernating bats had a stronger growth inhibitory effect on 3T3-L1 cells than that of non-hibernating bats. Structural modeling revealed that the structures of the receptor binding site III, which is critical for signal transduction, of the two bat leptins were very different. Similar to the human leptin, the leptin protein of non-hibernating bats was predicted to have a random loop, whereas that of hibernating bats had a helical structure in this region. This observation provided a clue as to the differential effects of the two different leptins on 3T3-L1 cells.

Role of leptin in delayed embryonic development in the Indian short-nosed fruit bat, Cynopterus sphinx

An adiposity-associated rise in leptin occurs at the time of delayed embryonic development in Cynopterus sphinx. The aim of present study was to examine the mechanism by which leptin may inhibit progesterone, and therefore could be responsible for delayed development. The study showed a significant increase in circulating leptin level during the period of increased fat accumulation, which coincided with significant decrease in serum progesterone level and delayed embryonic development in C. sphinx. The study showed increased Ob-R expression in the corpus luteum and in the utero-embryonic unit during the period of delayed embryonic development. The in vitro study showed suppressive effect of leptin on progesterone synthesis. The effect of high dose of leptin on ovarian steroidogenesis was found to be mediated through decreased expression of StAR and LH-R proteins in the ovary. The treatment with leptin caused increased expression of STAT 3 and iNOS proteins in the ovary, which correlated with decreased expression of StAR protein in the ovary. The inhibitory effects of leptin on progesterone synthesis in the ovary are thus mediated through STAT 3 and iNOS-NO signaling pathways. This study further demonstrated low expression of PCNA coinciding with the increased concentration of the leptin receptor in the utero-embryonic unit and high circulating leptin level during November. In conclusion, adiposity associated increased leptin level during November-December might play role in suppressing progesterone synthesis in the corpus luteum as well as suppressing the rate of cell-proliferation in the utero-embryonic unit thereby causing delayed embryonic development in C. sphinx.

Role of leptin in seasonal adiposity associated changes in testicular activity of vespertilionid bat, Scotophilus heathi

The aim of this study was to investigate changes in circulating level of leptin in natural population of male bat, Scotophilus heathi in relation to seasonal changes in body mass, adipose tissue mass and testicular activity. The peak serum leptin level coincided with the period of maximum body mass due to heavy accumulation of adipose tissue. The in vivo study showed both inhibitory and stimulatory effects on testicular activity depending on circulating level of leptin. Moderate increase in circulating concentration of leptin coincided with the stimulatory effect on testicular activity in October, whereas peak circulating concentration of leptin coincided with suppressed testicular activity in December. Immunohistochemical and Western blot analysis confirmed expression of leptin receptors (Ob-R) in the testis, particularly in Leydig cells during different reproductive stages suggesting the direct action of leptin in regulation of testicular steroidogenesis. The in vitro study confirmed the in vivo observations of inhibitory effect of leptin on testosterone production through dose-dependent StAR expression in the testis. This study further showed that the leptin affects testicular activity through STAT3 mediated regulation of StAR expression. Thus, increased adiposity associated rise in circulating leptin level during winter dormancy impairs testicular activity by suppressing StAR mediated testosterone production in S. heathi. These results are suggestive of a link between the adipocyte derived leptin and testicular function.

Melatonin affects steroidogenesis and delayed ovulation during winter in vespertilionid bat, Scotophilus heathi

The aim of this study was to evaluate the role of melatonin in ovarian activity of Scotophilus heathi particularly in reference to changes in steroidogenesis and steroid receptor expression during the anovulatory period of delayed ovulation. Female S. heathi showed an increased circulating melatonin level during the period of delayed ovulation in winter coinciding with the increased androstenedione (A(4)) levels, body fat and ovarian androgen receptor expression. The circulating melatonin level decreased to a low level after winter during the period of ovulation in March which also coincided with the decreased circulating A(4) levels and body fat. The circulating estrogen (E(2)) showed two peaks corresponding with the two waves of follicular development in November and February. Both the isoforms of progesterone receptor (PR), PR-A and PR-B, remained high throughout the follicular development, but expression of PR-A declined significantly during the ovulation. The treatment with melatonin, both in vitro and in vivo, significantly increased progesterone and A(4), but not the estradiol synthesis by the ovaries of S. heathi. The study further suggested that the increased androgens during winter may be primarily due to the stimulatory effect of melatonin on steroidogenic enzyme 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity. Therefore the increased circulating melatonin level in S. heathi during winter delay (inhibits) ovulation through increased androgen synthesis, but suppression of estradiol synthesis.

Melatonin regulates delayed embryonic development in the short-nosed fruit bat, Cynopterus sphinx

The aim of the present study was to evaluate the seasonal variation in serum melatonin levels and their relationship to the changes in the serum progesterone level, ovarian steroidogenesis, and embryonic development during two successive pregnancies of Cynopterus sphinx. Circulating melatonin concentrations showed two peaks; one coincided with the period of low progesterone synthesis and delayed embryonic development, whereas the second peak coincided with regressing corpus luteum. This finding suggests that increased serum melatonin level during November–December may be responsible for delayed embryonic development by suppressing progesterone synthesis. The study showed increased melatonin receptors (MTNR1A and MTNR1B) in the corpus luteum and in the utero–embryonic unit during the period of delayed embryonic development. The in vitro study showed that a high dose of melatonin suppressed progesterone synthesis, whereas a lower dose of melatonin increased progesterone synthesis by the ovary. The effects of melatonin on ovarian steroidogenesis are mediated through changes in the expression of peripheral-type benzodiazepine receptor, P450 side chain cleavage enzyme, and LH receptor proteins. This study further showed a suppressive impact of melatonin on the progesterone receptor (PGR) in the utero–embryonic unit; this effect might contribute to delayed embryonic development in C. sphinx. The results of the present study thus suggest that a high circulating melatonin level has a dual contribution in retarding embryonic development in C. sphinx by impairing progesterone synthesis as well as by inhibiting progesterone action by reducing expression of PGR in the utero–embryonic unit.

Endocrine function in naturally long-living small mammals

The complex, highly integrative endocrine system regulates all aspects of somatic maintenance and reproduction and has been widely implicated as an important determinant of longevity in short-lived traditional model organisms of aging research. Genetic or experimental manipulation of hormone profiles in mice has been proven to definitively alter longevity. These hormonally induced lifespan extension mechanisms may not necessarily be relevant to humans and other long-lived organisms that naturally show successful slow aging. Long-lived species may have evolved novel anti-aging defenses germane to naturally retarding the aging process. Here, we examine the available endocrine data associated with the vitamin D, insulin, glucocorticoid and thyroid endocrine systems of naturally long-living small mammals. Generally, long-living rodents and bats maintain tightly regulated lower basal levels of these key pleiotropic hormones than shorter lived rodents. Similarities with genetically manipulated long-lived rodent models of aging suggest that evolutionary well-conserved hormonal mechanisms are integrally involved in lifespan determination.

Luteal cell steroidogenesis in relation to delayed embryonic development in the Indian short-nosed fruit bat, Cynopterus sphinx

The primary aim of this study was to determine the possible cause of slow or delayed embryonic development in Cynopterus sphinx by investigating morphological and steroidogenic changes in the corpus luteum (CL) and circulating hormone concentrations during two pregnancies of a year. This species showed delayed post-implantational embryonic development during gastrulation of the first pregnancy. Morphological features of the CL showed normal luteinization during both pregnancies. The CL did not change significantly in luteal cell size during the delay period of the first pregnancy as compared with the second pregnancy. The circulating progesterone and 17beta-estradiol concentrations were significantly lower during the period of delayed embryonic development as compared with the same stage of embryonic development during the second pregnancy. We also showed a marked decline in the activity of 3beta-hydroxysteroid dehydrogenase, P450 side chain cleavage enzyme, and steroidogenic acute regulatory peptide in the CL during the delay period. This may cause low circulating progesterone and estradiol synthesis and consequently delay embryonic development. What causes the decrease in steroidogenic factors in the CL during the period of delayed development in C. sphinx is under investigation.