Doses Of Leptin Research Articles

The effect of leptin on prepulse inhibition in a developmental model of schizophrenia

Post-weaning social isolation is a developmental animal model of schizophrenia. Impairment of prepulse inhibition (PPI), possibly due to increased activity of the mesolimbic dopaminergic system, has frequently been reported in this model. There are some reports of increased level of leptin in schizophrenic patients. It has been shown that intracerebroventricular (ICV) injection of leptin decreases dopamine in the nucleus accumbens of rats. Here we investigated the effect of leptin on PPI impairment following social isolation. Five groups of Sprague-Dawley rats were reared post weaning in social or isolated conditions for 14 weeks. PPI was measured before treatment in week 12, and after ICV injection of vehicle or different doses of leptin (1, 5, and 10μg/5μl) in week 14. Results showed reduced PPI in untreated isolated compared to socially-reared rats in week 12 (p=0.009), but not in week 14 (p=0.45). Results also showed that leptin dose-dependently increased the basal PPI in isolated rats compared to vehicle, that was significant at a dose of 10μg (p=0.002). A considerable but non-significant effect of treatment with leptin on startle response (p=0.13) was seen. In conclusion, our results reveal that leptin significantly increases PPI in socially-isolated rats. The findings of this study suggest possible antipsychotic properties for leptin. We suggest further studies on the possible disruption of leptin signaling in schizophrenia, and also the possible interaction of leptin with therapeutic effects of second generation antipsychotics.

Abstract 436: Administering Leptin into the Rostral Ventral Lateral Medulla (RVLM) Augments Blood Pressure and Renal Sympathetic Nerve Activity

Initially described as a hormone that regulates energy homeostasis, we now know that leptin is an integrative hormone that responds to and regulates various systems, in particular, the renal sympathetic nervous system. The rostral ventral lateral medulla (RVLM) contains neurons which evoke changes of arterial blood pressure by controlling the tonic and phasic activation of sympathetic activity. Thus, we sought to determine if leptin regulates blood pressure and renal sympathetic activity within the RVLM. Utilizing immunohistochemistry, we observed that neurons within the RVLM that receive sympathetic projections from the kidney express leptin receptors on them. We have also demonstrated that these neurons are responsive to low doses of leptin and evoke significant increases in blood pressure, renal sympathetic nerve activity and heart rate. Taken together, these data demonstrate that leptin can regulate blood pressure and renal sympathetic nerve activity within the RVLM.

Leptin inhibits the reproductive axis in adult male Syrian hamsters exposed to long and short photoperiod

The aim of the study was to investigate the effects of acute leptin treatment of adult Syrian hamsters exposed to a long (LP, eugonadal males) and short photoperiod (SP, hypogonadal males). Animals were exposed to LP (L:D 14:10) or SP (L:D 10:14) for 10 weeks. Afterwards, both LP and SP hamsters were allocated to a control (SP-C, LP-C) or leptin-treated group (SP 3, SP 10, SP 30 or LP3, LP 10, LP 30). One hour before sacrifice, a single dose of leptin (3, 10 or 30μg/kg) or vehicle was administered (i.p.) to the males. Testis weight, serum and pituitary luteinizing hormone (LH) concentrations, as well as the hypothalamic concentration of gonadotropin-releasing hormone (GnRH) were recorded. Histological analysis of the testis was performed and GnRH concentration in the culture medium of hypothalamic explants was examined. A dramatic regression of testicular weight and histological atrophy of seminiferous tubules, as well as a decrease in serum and pituitary LH concentrations were found in SP males. All doses of leptin significantly reduced serum LH levels and medium GnRH concentrations in both photoperiod groups. Pituitary LH and hypothalamic GnRH concentrations were not affected by leptin. In conclusion, we demonstrated that leptin inhibited the reproductive axis of Syrian male hamsters exposed to LP and SP and fed ad libitum.

Leptin Administration Enhances Islet Transplant Performance in Diabetic Mice

Islet transplantation is an effective method to obtain long-term glycemic control for patients with type 1 diabetes, yet its widespread use is limited by an inadequate supply of donor islets. The hormone leptin has profound glucose-lowering and insulin-sensitizing action in type 1 diabetic rodent models. We hypothesized that leptin administration could reduce the dose of transplanted islets required to achieve metabolic control in a mouse model of type 1 diabetes. We first performed a leptin dose-response study in C57Bl/6 mice with streptozotocin (STZ)-induced diabetes to determine a leptin dose insufficient to reverse hyperglycemia. Subsequently, we compared the ability of suboptimal islet transplants of 50 or 125 syngeneic islets to achieve glycemic control in STZ-induced diabetic C57Bl/6 mice treated with or without this dose of leptin. The dose-response study revealed that leptin reverses STZ-induced diabetes in a dose-dependent manner. Supraphysiological leptin levels were necessary to restore euglycemia but simultaneously increased risk of hypoglycemia, and also lost efficacy after 12 days of administration. In contrast, 1 µg/day leptin only modestly reduced blood glucose but maintained efficacy throughout the study duration. We then administered 1 µg/day leptin to diabetic mice that underwent transplantation of 50 or 125 islets. Although these islet doses were insufficient to ameliorate hyperglycemia alone, coadministration of leptin with islet transplantation robustly improved control of glucose and lipid metabolism, without increasing circulating insulin levels. This study reveals that low-dose leptin administration can reduce the number of transplanted islets required to achieve metabolic control in STZ-induced diabetic mice.

Integrated Effects of Leptin in the Forebrain and Hindbrain of Male Rats

Leptin receptors (ObRs) in the forebrain and hindbrain have been independently recognized as important mediators of leptin responses. It is unclear how leptin activity in these areas is integrated. We tested whether both forebrain and hindbrain ObRs have to be activated simultaneously to change energy balance and to maintain metabolic homeostasis. Previous studies used acute leptin injections in either the third ventricle (1-5 μg) or the fourth ventricle (3-10 μg); here we used 12-day infusions of low doses of leptin in one or both ventricles (0.1 μg/24 h in third, 0.6 μg/24 h in fourth). Male Sprague Dawley rats were fitted with third and fourth ventricle cannulas, and saline or leptin was infused from Alzet pumps for 6 or 12 days. Rats that received leptin into only the third or the fourth ventricle were not different from controls that received saline in both ventricles. By contrast, rats with low-dose leptin infusions into both the third and fourth ventricle showed a dramatic 60% reduction in food intake that was reversed on day 6, a 20% weight loss that stabilized on day 6, and a 50% decrease in body fat at day 12 despite the correction of food intake. They displayed normal activity and maintained energy expenditure despite weight loss, indicating inappropriately high thermogenesis that coincided with increased signal transducer and activator of transcription 3 (STAT3) phosphorylation in the brainstem. Altogether, these findings show that with low doses of leptin, chronic activation of both hypothalamic and brainstem ObRs is required to reduce body fat.

Elevated skeletal muscle irisin precursor FNDC5 mRNA in obese OLETF rats

ObjectiveThere is debate as to whether fibronectin type III domain containing 5 (FNDC5) and its protein product irisin are therapeutic targets for obesity-associated maladies. Thus, we sought to examine FNDC5 mRNA within skeletal muscle of obese/diabetic-prone Otsuka Long-Evans Tokushima Fatty (OLETF) rats versus lean/healthy Long Evans Tokushima Otsuka (LETO) rats. We hypothesized that FNDC5 expression would be greater in obese (OLETF) versus lean (LETO) animals. Materials/MethodsTriceps muscle of 30–32week old OLETF and LETO rats were assayed for FNDC5 and PGC1α mRNA levels. Body composition and circulating biomarkers of the OLETF and LETO rats were also correlated with skeletal muscle FNDC5 mRNA expression patterns in order to examine potential relationships that may exist. ResultsOLETF rats exhibited twice the amount of triceps FNDC5 mRNA compared to LETO rats (p<0.01). Significant positive correlations existed between triceps muscle FNDC5 mRNA expression patterns versus fat mass (r=0.70, p=0.008), as well as plasma leptin (r=0.82, p<0.001). PGC1α mRNA levels were also highly correlated with FNDC5 mRNA (r=0.85, p<0.001). In subsequent culture experiments, low and high physiological doses of leptin had no effect on PGC1α mRNA or FNDC5 mRNA levels in C2C12 myotubes. Paradoxically, circulating irisin concentrations tended to be higher in a second cohort of LETO versus OLETF rats (p=0.085). ConclusionThese results reveal a positive association between total body adiposity and skeletal muscle FNDC5 gene expression. Of interest, circulating irisin levels tended to be lower in OLETF rats. Further research is needed to examine whether other adipose tissue-derived factors up-regulate FNDC5 transcription and/or inhibit irisin biosynthesis from FNDC5.

Detrimental Effects of Leptin on Intracerebral Hemorrhage via the STAT3 Signal Pathway

Leptin, one of the most important adipokines, is not only an energy regulator but also a regulator of innate immunity. Inflammation plays a key role in the tissue damage after intracerebral hemorrhage (ICH), and we sought to investigate whether leptin has a detrimental effect on ICH. After the injection of a high replacement dose (0.04 mg/kg) and two pharmacologic doses (4 and 8 mg/kg) of leptin, brain water contents increased significantly compared with that of control mice (P<0.05), which was confirmed when comparing the results with leptin-deficient ob/ob and wild-type (WT) mice (78.8%±0.6% versus 79.7%±0.6%, P<0.05). The number of Ox6-positive microglia/macrophages was increased in the leptin-injected group and decreased in ob/ob compared with WT mice. Among the candidate signal transducers, an increase in signal transduction and activator of transcription 3 (STAT3) levels was found after leptin injection. When we administered NSC74859, a specific inhibitor of phosphorylated STAT3 (pSTAT3), the water content became normalized. Activity of pSTAT3 was found mainly in Ox6-positive microglia/macrophages, but not in either neurons or astrocytes. We demonstrate that leptin plays a critical role in the secondary brain injury around a hematoma and is a novel mediator of the inflammation. This detrimental effect of leptin on ICH is mediated by the STAT3 signaling pathway in inflammatory cells.

Different levels of leptin regulate different target enzymes involved in progesterone synthesis

To study the effects of different doses of leptin on the expression of proteins involved in P synthesis, such as steroidogenic acute regulatory protein (StAR), cytochrome P450 side chain cleavage (P450scc), and 3β-hydroxysteroid dehydrogenase (3βHSD). Experimental studies. Research laboratory. Immature rats primed with gonadotropins to induce ovulation. Invivo studies: rats received either an acute or daily treatment with leptin. Invitro studies: ovarian explants were cultured in the absence or presence of leptin (0.3-500 ng/mL). The expression of both messenger RNA and protein of StAR, P450scc, and 3βHSD were measured by reverse transcription-polymerase chain reaction (PCR) and Western blot, respectively. The acute treatment with leptin, which inhibits the ovulatory process, caused a significant reduction in the ovarian expression of P450scc without changes in StAR or 3βHSD. In contrast, the daily treatment, which induces the ovulatory process, showed an increased expression of the ovarian 3βHSD protein, without differences in the other proteins measured. We also found that leptin increased the protein of both P450scc and 3βHSD at physiological levels and inhibited both messenger RNA and protein of 3βHSD at higher concentrations. The results indicate that 1) leptin is able to regulate the expression of the 3βHSD protein in a dose-dependent manner; and 2) leptin seems to exert its dual effects on P synthesis on different targets in a dose-dependent manner.

Perinatal programming of obesity: an introduction to the topic

Perinatal programming of obesity: an introduction to the topic

Leptin – A novel pharmacological agent for treatment of women with overactive bladder symptoms?

Overactive bladder is a common condition and is significantly known to affect quality of life in both men and women. It is usually associated with urinary urgency, frequency, nocturia with or without urinary incontinence. The exact aetiology of overactive bladder is unknown. The two main theories put forward include (a) disruption of central control of the bladder by excessive suprapontine excitation or reduced suprapontine inhibition (b) Peripheral abnormality due to excessive cholinergic excitation (increases release of acetylcholine which is calcium dependent) or reduced neuropeptidergic inhibition. The other factors which contribute to its cause include increase in caffeine intake and behavioural problems. Therefore the initial treatments are based on excluding pathology and implementing behavioural changes, bladder training and caffeine reduction. Anticholinergic drugs are the main pharmacological agents used in the treatment of overactive bladder and they are usually used in conjunction with the above treatment methods. Recently, an increase in serum leptin levels has been associated with overactive bladder symptoms. This possibly is not true because leptin actually reduces Ca2+ influx in the smooth muscle. The addition of increasing doses of leptin on uterine smooth muscle (in vitro) has shown to inhibit spontaneous as well as induced uterine contractions (myometrial biopsies taken from obese women) by reducing Ca2+ influx in obese women compared to normal weight women. We believe it may have similar action on the bladder and therefore expect inhibition of the bladder detrusor smooth muscle contraction rather than stimulation which may lead to overactive bladder symptoms. This action can be considered anticholinergic rather than cholinergic and therefore should improve overactive bladder symptoms. So could this hormone (leptin) be used as a new novel agent for treating women suffering with overactive bladder symptoms?

Leptin stimulation of cell cycle and inhibition of apoptosis gene and protein expression in OVCAR-3 ovarian cancer cells

The OVCAR-3 cell line expressing the long (ObRb) and short (ObRt) isoforms of leptin receptor mRNA was used to analyze the effect of leptin on the expression of selected genes and proteins involved in the cell cycle and apoptosis. OVCAR-3 cells were exposed to 2, 20, 40, and 100 ng/ml of leptin. Cell proliferation was determined using the alamarBlue cell viability test and flow cytometry. Apoptosis was measured using a cellular DNA fragmentation ELISA kit. The expression of selected cell cycle and apoptosis genes was evaluated by real-time PCR and confirmed by western blot. The stimulatory action of leptin on cell proliferation was observed as an increase in cells in the S and G2/M phases. Up-regulation of genes responsible for inducing cell proliferation and suppression of genes responsible for inhibition of proliferation were noted. Western blots revealed increased expression of cyclins D and A and inhibition of p21WAF1/CIP1 protein expression by leptin. Inhibition of DNA fragmentation was observed under all leptin doses. Suppression of genes involved in the extrinsic and intrinsic apoptotic pathway was observed. Western blots illustrated decreased Bad, TNFR1, and caspase 6 protein expression in response to leptin treatment. Leptin promotes ovarian cancer cell line growth by up-regulating genes and proteins responsible for inducing cell proliferation as well as down-regulating pro-apoptotic genes and proteins in apoptotic pathways. Results of this study warrant examining the relationship between the risk of ovarian cancer and elevated leptin levels in obese women.

Leptin Administration Improves Islet Transplant Efficacy in Streptozotocin-induced Diabetic Mice

Islet transplantation is a promising therapy to restore long-term glucose control for people with type 1 diabetes (T1D), but is limited by inadequate supply of donor tissue. High doses of leptin alone can reverse hyperglycemia in rodent models of T1D, yet can also produce hypoglycemia and leptin resistance. Thus we sought to determine whether low-dose leptin could instead be combined with islet transplantation, to reduce the amount of islets required to reverse diabetes in a mouse model of T1D. Streptozotocin-induced diabetic mice received suboptimal doses of 50 or 125 islets transplanted under the kidney capsule, along with either leptin (at a low dose that alone does not ameliorate diabetes) or vehicle for 6 weeks. Mice treated with 50 or 125 islets in the presence of leptin exhibited a robust reduction in fasted blood glucose levels within 12 days of surgery (15.4 ± 3.7 and 10.1 ± 5.7 mmol/L respectively) whereas mice transplanted with 50 or 125 islets in the absence of leptin remained diabetic throughout the study (blood glucose greater than 20 mmol/L). Furthermore, leptin treated recipients of 50 and 125 islets had improved glucose tolerance (∼28 and 27% lower area under the curve respectively), and reduced circulating lipids, β-hydroxybutryate, and hemoglobin A1c, compared to their vehicle treated controls. Thus, low-dose leptin administration can robustly improve the ability of a small number of transplanted islets to reverse hyperglycemia in streptozotocin-treated mice, and may be a potential avenue to reduce the amount of donor islets required to treat people with T1D.

In ovoleptin administration accelerates post‐hatch muscle growth and changes myofibre characteristics, gene expression and enzymes activity in broiler chickens

To evaluate the effect of maternal leptin on muscle growth, we injected 0 μg (control, CON), 0.5 μg (low leptin dose, LL) or 5.0 μg (high leptin dose, HL) of recombinant murine leptin dissolved in 100 μl of PBS into the albumen of broiler eggs prior to incubation. The newly hatched chicks were all raised under the same conditions until 21 days of age (D21), when body weight was measured and samples of gastrocnemius muscle were collected and weighed. Myosin ATPase staining was applied to identify myofibre types and measure the cross-sectional area (CSA) of myofibres. Real-time PCR was performed to quantify leptin receptor (LEPR), insulin-like growth factor 1 (IGF-1), IGF-1 receptor (IGF-1R), growth hormone receptor (GHR) and myostatin (MSTN) mRNA expression in the gastrocnemius muscle. The activity of calpains (CAPNs) in the gastrocnemius muscle was measured using a quantitative fluorescence detection kit. Male chickens treated with both high and low doses of leptin had significantly higher (p < 0.05) body weight on D21. The high leptin significantly increased the CSA (p < 0.05) of gastrocnemius muscle in male chickens, which coincided with a 93% increase (p < 0.05) in IGF-1 mRNA expression. Likewise, the LL dose increased the weight of gastrocnemius muscle in male chickens (p < 0.05), which was accompanied by a 41% down-regulation (p < 0.05) of MSTN mRNA expression and a decreased activity of CAPNs. However, all these changes were not observed in female chickens. The proportion of myofibre types did not altered. No significant change was detected for LEPR and GHR mRNA expression. These results indicate that in ovo leptin treatment affects skeletal muscle growth in chickens in a dose-dependent and sex-specific manner. The altered expression of IGF-1, MSTN mRNA and activity of CAPNs in skeletal muscle may be responsible for such effects.

An Overview of Molecular and Cellular Mechanisms Associated with Porcine Pregnancy Success or Failure

Prenatal mortality remains one of the major constraints for the commercial pig industry in North America. Twenty to thirty per cent of the conceptuses are lost early in gestation and an additional 10-15% is lost by mid-to-late gestation. Research over the last two decades has provided critical insights into how uterine capacity, placental efficiency, genetics, environment, nutrition and immune mechanisms impact successful conceptus growth; however, the exact cause and effect relationship in the context of foetal loss has yet to be determined. Similar to other mammalian species such as the human, mouse, rat, and primates, immune cell enrichment occurs at the porcine maternal-foetal interface during the window of conceptus attachment. However, unlike other species, immune cells are solely recruited by conceptus-derived signals. As pigs have epitheliochorial placentae where maternal and foetal tissue layers are separate, it provides an ideal model to study immune cell interactions with foetal trophoblasts. Our research is focused on the immune-angiogenesis axis during porcine pregnancy. It is well established that immune cells are recruited to the maternal-foetal interface, but their pregnancy specific functions and how the local milieu affects angiogenesis and inflammation at the site of foetal arrest remain unknown. Through a better understanding of how immune cells modulate crosstalk between the conceptus and the mother, it might be possible to therapeutically target immune cells and/or their products to reduce foetal loss. In this review, we provide evidence from the literature and from our own work into the immunological factors associated with porcine foetal loss.

Abstract 80: Differential expression of NILCO reveals pathogenesis of human breast cancer

Abstract Introduction: Notch, IL-1 and leptin are known pro-angiogenic factors linked to breast cancer (BC) development, aggressiveness and poor prognosis. We have recently reported leptin as an inducer of IL-1 and Notch in BC cells. Furthermore, we have unveiled a novel signaling crosstalk between these factors: NILCO (Notch, IL-1, leptin crosstalk outcome). Our data show NILCO impacts on VEGF/VEGFR2 levels in BC cells. Objective: In this investigation, we aim to elucidate differences in NILCO relationships to the pathogenesis of triple negative breast cancer (TNBC) as compared to ER positive BC. We hypothesize that the expression of NILCO components correlates to TNBC etiology. Methods: Expression levels of Notch 1, 4, Jagged 1, DLL4, VEGF/VEGFR2 (FLK-1), Ob, Ob-R and IL-1R tI were examined by immunohistochemistry (IHC) in tissue microarrays (n=75/duplicate from Pantomics, Inc.) BC samples included normal/hyperplastic specimens (n=3), fibroadenomas (n=2), invasive ductal carcinomas (n=62; 13 were TNBC: ER-, PR- and HER2/neu-), ductal carcinomas in situ (n=2) and Paget's disease (n=1). IHC evaluations were conducted by two independent observers using semi-quantitative analysis of staining [HSCORE = ∑pi (i + 1), where “i’” is the intensity of staining with a value of 1, 2 or 3 (weak, moderate or strong, respectively) and ‘pi’ is the percentage of stained cells for each intensity]. The following cell lines: TNBC (MDA-MB231 and HCC1806) and ER+ (T47D and MCF-7) were treated with increasing doses of human leptin; leptin peptide receptor antagonist, LPrA2 and a γ-secretase inhibitor (DAPT: Notch pathway inhibitor). After treatments, NILCO and targets were determined by western blot (WB) and ELISA. Results: Data from BC tissue array showed NILCO components were present in the majority of samples. However, lower expression of Notch1, leptin and IL-1R tI was found in non-malignant tissues. In general, TNBC overexpressed Notch1/leptin as compared to ER positive BC. ELISA and WB analysis of cell lysates revealed that leptin increased NILCO component/activation and targets in a dose-dependent manner. Both DAPT and LPrA2 reduced leptin's effects on NILCO. Conclusions: These results support the hypothesis that NILCO may play an important role in BC pathogenesis. [This work was supported in part by NIH/NCI1SC1CA138658-03; NIH/ARRA/3SC1CA138658-02S1 and the Georgia Cancer Coalition Distinguished Cancer Scholar Award (to RRGP); CREDO (MSCR) 2R25RR017694-06A1 to L.S.C; the Morehouse School of Medicine (MSM) MBRS RISE Program (NIH/NIGMS 506 GM08248) to T.Z.M; Blacksone Academy, NIH/NIDDK Step-up HS Research Program: Short-Term Education Program for Underrepresented Persons to K.W. and facilities and support services at Morehouse School of Medicine (NIH RR03034 and 1C06 RR18386)]. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 80. doi:1538-7445.AM2012-80

Abstract 785: Leptin-Notch-Wnt axis affects drug resistance in breast cancer

Abstract Introduction: Triple negative breast cancer (TNBC) is a particularly aggressive form of the disease whose incidence is disproportionate in obese African American and Latina women. TNBC is commonly associated with acute early onset, poor survival and acquired drug-resistance. Obesity, characterized by high levels of leptin, is frequently found among these ethnic groups. We hypothesize that intact leptin-Notch-Wnt signaling crosstalk affects the development of drug-resistance in TNBC. Objective: To determine whether leptin signaling induces Notch/Wnt pathway crosstalk, decreasing the effectiveness of cisplatin in TNBC cells. Materials &amp; Methods: TNBC cells (MDA MB 231 and HCC1806) and ER+ MCF-7 (as control) were treated with pharmacological doses of leptin and agonists of the Notch and Wnt pathways JAG1-17 mer peptide and Wnt-1, respectively. In addition, the cells were challenged with the leptin receptor, Notch pathway, and Wnt pathway antagonists LPrA2, DAPT, and Wnt-1 respectively. The impact of these molecules on cisplatin anti-cancer effects was also determined. Activation of Wnt (total/pβ-catenin), expression of Notch (Notch 1-4 and JAG1/Dll-4 and targets: survivin/Hey2), cell proliferation and apoptosis were determined by Western blot and flow cytometry. β-catenin levels were also investigated by immunofluorescence. We also determined the impact of the inhibition of leptin signaling (via LPrA2) on the expression of Wnt and Notch in DMBA-induced breast cancer from DIO (diet-induced obese) mice. Results: We found that leptin increased the levels of β-catenin mainly in TNBC cells. Similarly, inhibition of leptin signaling decreased Wnt/Notch expression in DMBA/DIO-breast cancer. Interestingly, leptin increased expression of Notch and attenuated the detrimental effects of cisplatin on breast cancer cells. Wnt-1 affected Notch levels but its effects were less pronounced. Conclusions: Leptin is able to induce the Notch and Wnt signaling pathways in breast cancer. Cisplatin effects were attenuated by leptin in TNBC probably through its crosstalk with Wnt and Notch signaling pathways. These results are particularly relevant for TNBC and obese patients, and suggest that leptin inhibition could be useful in increasing the chemotherapeutic effectiveness in TBNC by disrupting leptin-Wnt-Notch crosstalk. [This work was supported in part by NIH/NCI1SC1CA138658-02; NIH/ARRA/3SC1CA138658-02S1 and the Georgia Cancer Coalition Distinguished Cancer Scholar Award (to RRGP); CREDO (MSCR) 2R25RR017694-06A1 (to L.S.C); NIH/NIGMS R25 GM058268 and NCRR 5P20RR11104 (to T.Z.M); and facilities and support services at MSM (NIH RR03034 and 1C06 RR18386)]. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 785. doi:1538-7445.AM2012-785

Leptin acts in the forebrain to increase gain of baroreflex control of lumbar sympathetic nerve activity and heart rate

Leptin increases lumbar sympathetic nerve activity (LSNA), but whether leptin also enhances baroreflex control of LSNA and heart rate (HR) is unclear. To test this hypothesis, leptin was infused into the lateral cerebroventricle (ICV) of α‐chloralose anesthetized male SD rats. Baroreflex function was assessed hourly for 2 hrs using a 4 parameter sigmoidal fit of HR and LSNA responses to slow ramp (3–5 min) changes in arterial pressure (AP), induced by iv infusion of nitroprusside and phenylephrine. After 2 hr, leptin (3μg, n=5) increased (P&lt;0.05) the maximum gain (BRG) of LSNA (from 4.0±0.6 to 6.9±1.4 %/mmHg) and HR (from 2.5±0.2 to 3.4±0.5 bpm/mmHg), as well as LSNA (to 204±20 % control), HR (from 327±6 to 395±13 bpm), the reflex LSNA maximum (from 185±12 to 370 ± 38%), the HR maximum (from 399±12 to 472±20 bpm), and mean AP (from 111±3 to124±4 mmHg). A lower dose of leptin (1.5 μg; n=5) transiently increased LSNA BRG at 1 hr (from 3.1±0.6 to 5.5±1.2 %/mmHg; P&lt;0.05); other parameters were not significantly altered. ICV infusion of the artificial CSF vehicle (n=5) had no effects. To test if leptin acts in the brainstem to improve baroreflex function, leptin (3 μg) was infused into the 4th ventricle (n=4). However, no significant changes in LSNA BRG (4.2±0.5 to 4.1±0.5 %/mmHg), HR BRG (2.2 ±0.6 to 2.3±0.5 bpm /mmHg), or other parameters were observed. In conclusion, leptin acts in the forebrain to enhance baroreflex control of HR and LSNA, by increasing BRG and maximum reflex HR and LSNA. Support: HL088552.

Leptin anti‐apoptotic mechanisms in LPS‐induced PC12 cells

Evidence indicates that leptin has neuroprotective properties as it protects neurons from a variety of neurotoxic agents. However, leptin mechanisms have not been well studied. This study evaluated the anti‐apoptotic effects of leptin in LPS‐induced PC12 cells. Cells were pretreated with varying doses of leptin for 2 hours before stimulation with LPS for 48 hours. The results showed that LPS decreased cell viability, while pretreatment with leptin increased it in a dose‐dependent manner, as measured with MTT assay. Furthermore, western blot analysis showed a dose‐dependent reduction in the expression of cyclophilin D (CypD), an important component in the apoptosis pathway. The anti‐apoptotic effect of leptin was confirmed by the decrease in the expression of pro‐apoptotic protein Bad, and the increase in the expression of anti‐apoptotic protein BcL2. The present study indicates that leptin or its analogs, through inhibition of apoptosis may be promising novel therapeutic agents for the treatment of neurodegenerative diseases such as AD.

Caprine cauda epididymal sperm motility pattern in the capacitation medium supplemented with leptin

Leptin is an adipocyte-derived hormone with a role in the reproductive system through metabolic signals. Studies have suggested that binding of leptin to its receptors which have been found in human and boar sperm activates biochemical pathways leading to sperm capacitation. The present study was designed to explore the effects of leptin on sperm kinetic pattern during capacitation in vitro. Epididymal spermatozoa were obtained from 30 adult goat testes in six replicates and incubated in capacitation medium (Ca2+-free Tyrode’s medium, Sperm-TALP) supplemented with 0 (Con, control group), 10 and 100 ng/mL (L10 and L100 groups, respectively). Motion parameters were assessed using computer-assisted sperm analysis system at 10, 30, 60, 120 and 240 min after sperm incubation at 37°C and 6 % CO2. Exposure of spermatozoa to two different doses of leptin caused a significant increase (p < 0.05) in total and progressive sperm motility, curvilinear and straight line velocity, linearity (Lin), mean angular displacement, amplitude of lateral head displacement (ALH) and beat cross-frequency (BCF) compared to the control group specially up to 60 min. There was not any significant difference between L10 and L100 groups in the evaluated parameters except for the first 10 min that L100 had better result in increasing Lin, ALH and BCF (p < 0.05) and at the time of 240 min in which L10 showed a significant increase in all motion parameters. In conclusion, this study showed that leptin supplementation had significant effects on sperm motility patterns and so could enhance the sperm capacitation process.

Leptin regulates estrogen receptor gene expression in ATDC5 cells through the extracellular signal regulated kinase signaling pathway

Both estrogen and leptin play an important role in the regulation of physiological processes of endochondral bone formation in linear growth. Estrogen receptors (ERα and ERβ) are known as members of the superfamily of nuclear steroid hormone receptors and are detected in all zones of growth plate chondrocytes. They can be regulated in a ligand-independent manner. Whether leptin regulates ERs in the growth plate is still not clear. To explore this issue, chondrogenic ATDC5 cells were used in the present study. Messenger RNA and protein analyses were performed by quantitative PCR and Western blotting. We found that both ERα and ERβ were dynamically expressed during the ATDC5 cell differentiation for 21 days. Leptin (50 ng/ml) significantly upregulated ERα and ERβ mRNA and protein levels 48 h after leptin stimulation (P<0.05) at day 14. The up-regulation of ERα and ERβ mRNA by leptin was shown in a dose-dependent manner, but the most effective dose of leptin was different (100 and 1,000 ng/ml, respectively). Furthermore, we confirmed that leptin augmented the phosphorylation of ERK1/2 in a time-dependent manner. A maximum eightfold change was observed at 15 min. Finally, a specific ERK1/2 inhibitor, UO126, blocked leptin-induced ERs regulation in ATDC5 cells, indicating that ERK1/2 mediates, partly, the effects of leptin on ERs. These data demonstrate, for the first time, that leptin regulates the expression of ERs in growth plate chondrocytes via ERK signaling pathway, thereby suggesting a crosstalk between leptin and estrogen receptors in the regulation of bone formation.