Angela M. Ramos-Lobo

Inactivation of SOCS3 in leptin receptor-expressing cells protects mice from diet-induced insulin resistance but does not prevent obesity

Therapies that improve leptin sensitivity have potential as an alternative treatment approach against obesity and related comorbidities. We investigated the effects of Socs3 gene ablation in different mouse models to understand the role of SOCS3 in the regulation of leptin sensitivity, diet-induced obesity (DIO) and glucose homeostasis. Neuronal deletion of SOCS3 partially prevented DIO and improved glucose homeostasis. Inactivation of SOCS3 only in LepR-expressing cells protected against leptin resistance induced by HFD, but did not prevent DIO. However, inactivation of SOCS3 in LepR-expressing cells protected mice from diet-induced insulin resistance by increasing hypothalamic expression of Katp channel subunits and c-Fos expression in POMC neurons. In summary, the regulation of leptin signaling by SOCS3 orchestrates diet-induced changes on glycemic control. These findings help to understand the molecular mechanisms linking obesity and type 2 diabetes, and highlight the potential of SOCS3 inhibitors as a promising therapeutic approach for the treatment of diabetes.

Prolactin-sensitive neurons express estrogen receptor-α and depend on sex hormones for normal responsiveness to prolactin.

Estrogens and prolactin share important target tissues, including the gonads, brain, liver, kidneys and some types of cancer cells. Herein, we sought anatomical and functional evidence of possible crosstalk between prolactin and estrogens in the mouse brain. First, we determined the distribution of prolactin-responsive neurons that express the estrogen receptor α (ERα). A large number of prolactin-induced pSTAT5-immunoreactive neurons expressing ERα mRNA were observed in several brain areas, including the anteroventral periventricular nucleus, medial preoptic nucleus, arcuate nucleus of the hypothalamus, ventrolateral subdivision of the ventromedial nucleus of the hypothalamus (VMH), medial nucleus of the amygdala and nucleus of the solitary tract. However, although the medial preoptic area, periventricular nucleus of the hypothalamus, paraventricular nucleus of the hypothalamus, retrochiasmatic area, dorsomedial subdivision of the VMH, lateral hypothalamic area, dorsomedial nucleus of the hypothalamus and ventral premammillary nucleus contained significant numbers of prolactin-responsive neurons, these areas showed very few pSTAT5-immunoreactive cells expressing ERα mRNA. Second, we evaluated prolactin sensitivity in ovariectomized mice and observed that sex hormones are required for a normal responsiveness to prolactin as ovariectomized mice showed a lower number of prolactin-induced pSTAT5 immunoreactive neurons in all analyzed brain nuclei compared to gonad-intact females. In addition, we performed hypothalamic gene expression analyses to determine possible post-ovariectomy changes in components of prolactin signaling. We observed no significant changes in the mRNA expression of prolactin receptor, STAT5a or STAT5b. In summary, sex hormones exert a permissive role in maintaining the brains prolactin sensitivity, most likely through post-transcriptional mechanisms.

SOCS3 deficiency in leptin receptor-expressing cells mitigates the development of pregnancy-induced metabolic changes

Objective During pregnancy, women normally increase their food intake and body fat mass, and exhibit insulin resistance. However, an increasing number of women are developing metabolic imbalances during pregnancy, including excessive gestational weight gain and gestational diabetes mellitus. Despite the negative health impacts of pregnancy-induced metabolic imbalances, their molecular causes remain unclear. Therefore, the present study investigated the molecular mechanisms responsible for orchestrating the metabolic changes observed during pregnancy. Methods Initially, we investigated the hypothalamic expression of key genes that could influence the energy balance and glucose homeostasis during pregnancy. Based on these results, we generated a conditional knockout mouse that lacks the suppressor of cytokine signaling-3 (SOCS3) only in leptin receptor-expressing cells and studied these animals during pregnancy. Results Among several genes involved in leptin resistance, only SOCS3 was increased in the hypothalamus of pregnant mice. Remarkably, SOCS3 deletion from leptin receptor-expressing cells prevented pregnancy-induced hyperphagia, body fat accumulation as well as leptin and insulin resistance without affecting the ability of the females to carry their gestation to term. Additionally, we found that SOCS3 conditional deletion protected females against long-term postpartum fat retention and streptozotocin-induced gestational diabetes. Conclusions Our study identified the increased hypothalamic expression of SOCS3 as a key mechanism responsible for triggering pregnancy-induced leptin resistance and metabolic adaptations. These findings not only help to explain a common phenomenon of the mammalian physiology, but it may also aid in the development of approaches to prevent and treat gestational metabolic imbalances.

Leptin Resistance Is Not the Primary Cause of Weight Gain Associated With Reduced Sex Hormone Levels in Female Mice

Several studies have shown that estrogens mimic leptins effects on energy balance regulation. However, the findings regarding the consequences of reduced sex hormone levels on leptin sensitivity are divergent. In the present study, we employed different experimental paradigms to elucidate the interaction between estrogens, leptin, and energy balance regulation. We confirmed previous reports showing that ovariectomy caused a reduction in locomotor activity and energy expenditure leading mice to obesity and glucose intolerance. However, the acute and chronic anorexigenic effects of leptin were preserved in ovariectomized (OVX) mice despite their increased serum leptin levels. We studied hypothalamic gene expression at different time points after ovariectomy and observed that changes in the expression of genes involved in leptin resistance (suppressors of cytokine signaling and protein-tyrosine phosphatases) did not precede the early onset of obesity in OVX mice. On the contrary, reduced sex hormone levels caused an up-regulation of the long form of the leptin receptor (LepR), resulting in increased activation of leptin signaling pathways in OVX leptin-treated animals. The up-regulation of the LepR was observed in long-term OVX mice (30 d or 24 wk after ovariectomy) but not 7 days after the surgery. In addition, we observed a progressive decrease in the coexpression of LepR and estrogen receptor-α in the hypothalamus after the ovariectomy, resulting in a low percentage of dual-labeled cells in OVX mice. Taken together, our findings suggest that the weight gain caused by reduced sex hormone levels is not primarily caused by induction of a leptin-resistance state.

Chronic sleep restriction promotes brain inflammation and synapse loss, and potentiates memory impairment induced by amyloid-β oligomers in mice

It is increasingly recognized that sleep disturbances and Alzheimers disease (AD) share a bidirectional relationship. AD patients exhibit sleep problems and alterations in the regulation of circadian rhythms; conversely, poor quality of sleep increases the risk of development of AD. The aim of the current study was to determine whether chronic sleep restriction potentiates the brain impact of amyloid-β oligomers (AβOs), toxins that build up in AD brains and are thought to underlie synapse damage and memory impairment. We further investigated whether alterations in levels of pro-inflammatory mediators could play a role in memory impairment in sleep-restricted mice. We found that a single intracerebroventricular (i.c.v.) infusion of AβOs disturbed sleep pattern in mice. Conversely, chronically sleep-restricted mice exhibited higher brain expression of pro-inflammatory mediators, reductions in levels of pre- and post-synaptic marker proteins, and exhibited increased susceptibility to the impact of i.c.v. infusion of a sub-toxic dose of AβOs (1pmol) on performance in the novel object recognition memory task. Sleep-restricted mice further exhibited an increase in brain TNF-α levels in response to AβOs. Interestingly, memory impairment in sleep-restricted AβO-infused mice was prevented by treatment with the TNF-α neutralizing monoclonal antibody, infliximab. Results substantiate the notion of a dual relationship between sleep and AD, whereby AβOs disrupt sleep/wake patterns and chronic sleep restriction increases brain vulnerability to AβOs, and point to a key role of brain inflammation in increased susceptibility to AβOs in sleep-restricted mice.

Neuronal STAT5 signaling is required for maintaining lactation but not for postpartum maternal behaviors in mice

Prolactin and placental lactogens control mammary development and lactation as well as play an important role in maternal behaviors. However, the molecular mechanisms in the brain responsible for this regulation remain largely unknown. Therefore, the present study investigated whether Signal Transducer and Activator of Transcription 5 (STAT5) signaling in the brain, the key transcriptional factor recruited by prolactin receptor and other hormones, is required for postpartum maternal behavior, maintenance of lactation and offspring growth. Neuronal ablation of STAT5 impaired the control of prolactin secretion and reduced the hypothalamic expression of suppressors of cytokine signaling (i.e., SOCS3 and CISH). In addition, neuronal STAT5 deletion attenuated the hyperphagia commonly observed during lactation by decreasing the hypothalamic expression of orexigenic neurotransmitters such as the neuropeptide Y and agouti-related protein. The lower food intake of lactating neuron-specific STAT5 knockout females resulted in reduced milk production and offspring growth. Unexpectedly, postpartum maternal behavior expression was not impaired in neuron-specific STAT5 knockout females. On the contrary, the latency to retrieve and group the pups into the nest was reduced in mutant dams. Finally, we demonstrated that approximately 30% of recorded neurons in the medial preoptic area were acutely depolarized by prolactin suggesting that fast STAT5-independent signaling pathways may be involved in the regulation of maternal behaviors. Overall, our results revealed important information about the molecular mechanisms recruited by hormones to orchestrate the activation of neural circuitries engaged in the induction of maternal care.

Obesity impairs lactation performance in mice by inducing prolactin resistance

Obesity reduces breastfeeding success and lactation performance in women. However, the mechanisms involved are not entirely understood. In the present study, female C57BL/6 mice were chronically exposed to a high-fat diet to induce obesity and subsequently exhibited impaired offspring viability (only 15% survival rate), milk production (33% reduction), mammopoiesis (one-third of the glandular area compared to control animals) and postpartum maternal behaviors (higher latency to retrieving and grouping the pups). Reproductive experience attenuated these defects. Diet-induced obese mice exhibited high basal pSTAT5 levels in the mammary tissue and hypothalamus, and an acute prolactin stimulus was unable to further increase pSTAT5 levels above basal levels. In contrast, genetically obese leptin-deficient females showed normal prolactin responsiveness. Additionally, we identified the expression of leptin receptors specifically in basal/myoepithelial cells of the mouse mammary gland. Finally, high-fat diet females exhibited altered mRNA levels of ERBB4 and NRG1, suggesting that obesity may involve disturbances to mammary gland paracrine circuits that are critical in the control of luminal progenitor function and lactation. In summary, our findings indicate that high leptin levels are a possible cause of the peripheral and central prolactin resistance observed in obese mice which leads to impaired lactation performance.

Brain STAT5 signaling and behavioral control

Several growth factors and cytokines recruit the signal transducer and activator of transcription 5 (STAT5) signaling pathway to control cell proliferation, differentiation and apoptosis. Nonetheless, the importance of this transcription factor for brain functions is still poorly understood. Because some STAT5-inducing hormones, such as prolactin and leptin, act in the brain to regulate the expression of motivated behaviors, this signaling pathway is likely involved in behavioral modulation. Therefore, the objective of the present review was to summarize and discuss the available data regarding the possible role of central STAT5 signaling in the regulation of brain functions, especially on behavioral control. We discussed studies that investigated the importance of STAT5 signaling in the regulation of maternal and feeding behaviors. Additionally, we highlighted other behaviors that could be potentially affected by STAT5 signaling. This knowledge may help to understand how motivated behaviors are regulated at the cellular level.

The role of leptin in health and disease

ABSTRACT Leptin is a master regulator of energy balance and body adiposity. Additionally, leptin exerts important control on glucose homeostasis, thermogenesis, autonomic nervous system and neuroendocrine axes. In metabolic diseases, such as obesity and diabetes mellitus, leptin signaling may be compromised, indicating the important role of this hormone in the etiology and pathophysiological manifestations of these conditions. In the present manuscript, we reviewed important concepts of leptin signaling, as well as about the effects of leptin on several biologic functions. We also discussed the possible therapeutic use of leptin administration and how our current obesogenic environment contributes to the development of leptin resistance. Our objective was to provide a comprehensive and state-of-the-art review about the importance of leptin to maintain the homeostasis and during pathological conditions.

Maternal metabolic adaptations are necessary for normal offspring growth and brain development

Several metabolic adaptations emerge during pregnancy and continue through lactation, including increases in food intake and body weight, as well as insulin and leptin resistance. These maternal adaptations are thought to play a role in offspring viability and success. Using a model of attenuated maternal metabolic adaptations induced by ablation of the Socs3 gene in leptin receptor expressing cells (SOCS3 KO mice), our study aimed to investigate whether maternal metabolic changes are required for normal offspring development, and if their absence causes metabolic imbalances in adulthood. The litters were subjected to a cross‐fostering experimental design to distinguish the prenatal and postnatal effects caused by maternal metabolic adaptations. Males either born or raised by SOCS3 KO mice showed reduced body weight until 8 weeks of life. Both adult males and females born or raised by SOCS3 KO mice also had lower body adiposity. Despite that, no significant changes in energy expenditure, glucose tolerance or insulin resistance were observed. However, males either born or raised by SOCS3 KO mice showed reduced brain mass in adulthood. Furthermore, animals born from SOCS3 KO mice also had lower proopiomelanocortin fiber density in the paraventricular nucleus of the hypothalamus. In conclusion, these findings indicate that the commonly observed metabolic changes in pregnancy and lactation are necessary for normal offspring growth and brain development.