Effects of hypothalamic neurodegeneration on energy balance

Normal aging in humans and rodents is accompanied by a progressive increase in adiposity. To investigate the role of hypothalamic neuronal circuits in this process, we used a Cre-lox strategy to create mice with specific and progressive degeneration of hypothalamic neurons that express agouti-related protein (Agrp) or proopiomelanocortin (Pomc), neuropeptides that promote positive or negative energy balance, respectively, through their opposing effects on melanocortin receptor signaling. In previous studies, Pomc mutant mice became obese, but Agrp mutant mice were surprisingly normal, suggesting potential compensation by neuronal circuits or genetic redundancy. Here we find that Pomc-ablation mice develop obesity similar to that described for Pomc knockout mice, but also exhibit defects in compensatory hyperphagia similar to what occurs during normal aging. Agrp-ablation female mice exhibit reduced adiposity with normal compensatory hyperphagia, while animals ablated for both Pomc and Agrp neurons exhibit an additive interaction phenotype. These findings provide new insight into the roles of hypothalamic neurons in energy balance regulation, and provide a model for understanding defects in human energy balance associated with neurodegeneration and aging.     

Expanding neurotransmitters in the hypothalamic neurocircuitry for energy balance regulation

The current epidemic of obesity and its associated metabolic syndromes impose unprecedented challenges to our society. Despite intensive research on obesity pathogenesis, an effective therapeutic strategy to treat and cure obesity is still lacking. Exciting studies in last decades have established the importance of the leptin neural pathway in the hypothalamus in the regulation of body weight homeostasis. Important hypothalamic neuropeptides have been identified as critical neurotransmitters from leptin-sensitive neurons to mediate leptin action. Recent research advance has significantly expanded the list of neurotransmitters involved in body weight-regulating neural pathways, including fast-acting neurotransmitters, gamma-aminobutyric acid (GABA) and glutamate. Given the limited knowledge on the leptin neural pathway for body weight homeostasis, understanding the function of neurotransmitters released from key neurons for energy balance regulation is essential for delineating leptin neural pathway and eventually for designing effective therapeutic drugs against the obesity epidemic.     

Work life balance?

There is no perfect recipe to balance work and life in academic research. Everyone has to find their own optimal balance to derive fulfilment from life and work. Subject Categories: S&S: Careers & Training

A few years ago, a colleague came into my office, looking a little irate, and said, “I just interviewed a prospective student, and the first question was, ‘how is work‐life balance here?’”. Said colleague then explained how this question was one of his triggers. Actually, this sentiment isn''t unusual among many PIs. And, yet, asking about one''s expected workload is a fair question. While some applicants are actually coached to ask it at interviews, I think that many younger scientists have genuine concerns about whether or not they will have enough time away from the bench in order to have a life outside of work.In a nutshell, I believe there is no one‐size‐fits‐all definition of work–life balance (WLB). I also think WLB takes different forms depending on one''s career stage. As a new graduate student, I didn''t exactly burn the midnight oil; it took me a couple of years to get my bench groove on, but once I did, I worked a lot and hard. I also worked on weekends and holidays, because I wanted answers to the questions I had, whether it was the outcome of a bacterial transformation or the result from a big animal experiment. As a post‐doc, I worked similarly hard although I may have actually spent fewer hours at the bench because I just got more efficient and because I read a lot at home and on the six train. But I also knew that I had to do as much as I could to get a job in NYC where my husband was already a faculty member. The pressure was high, and the stress was intense. If you ask people who knew me at the time, they can confirm I was also about 30 pounds lighter than I am now (for what it''s worth, I was far from emaciated!).As an assistant professor, I still worked a lot at the bench in addition to training students and writing grant applications (it took me three‐plus years and many tears to get my first grant). As science started to progress, work got even busier, but in a good way. By no means did I necessarily work harder than those around me—in fact, I know I could have worked even more. And I’m not going to lie, there can be a lot of guilt associated with not working as much as your neighbor.My example is only one of millions, and there is no general manual on how to handle WLB. Everyone has their own optimal balance they have to figure out. People with children or other dependents are particularly challenged; as someone without kids, I cannot even fathom how tough it must be. Even with some institutions providing child care or for those lucky enough to have family take care of children, juggling home life with “lab life” can create exceptional levels of stress. What I have observed over the years is that trainees and colleagues with children become ridiculously efficient; they are truly remarkable. One of my most accomplished trainees had two children, while she was a post‐doc and she is a force to be reckoned with—although no longer in my laboratory, she still is a tour de force at work, no less with child number three just delivered! I think recruiters should view candidates with families as well—if not better—equipped to multi‐task and get the job done.There are so many paths one can take in life, and there is no single, “correct” choice. If I had to define WLB, I would say it is whatever one needs to do in order to get the work done to one''s satisfaction. For some people, putting in long days and nights might be what is needed. Does someone who puts in more hours necessarily do better than one who doesn''t, or does a childless scientist produce more results than one with kids? Absolutely not. People also have different goals in life: Some are literally “wedded” to their work, while others put much more emphasis on spending time with their families and see their children grow up. Importantly, these goals are not set in stone and can fluctuate throughout one''s life. Someone recently said to me that there can be periods of intense vertical growth where “balance” is not called for, and other times in life where it is important and needed. I believe this sentiment eloquently sums up most of our lives.Now that I''m a graying, privileged professor, I have started to prioritize other areas of life, in particular, my health. I go running regularly (well, maybe jog very slowly), which takes a lot of time but it is important for me to stay healthy. Pre‐pandemic, I made plans to visit more people in person as life is too short not to see family and friends. In many ways, having acquired the skills to work more efficiently after many years in the laboratory and office, along with giving myself more time for my health, has freed up my mind to think of science differently, perhaps more creatively. It seems no matter how much I think I’m tipping the balance toward life, work still creeps in, and that’s perfectly OK. At the end of the day, my work is my life, gladly, so I no longer worry about how much I work, nor do I worry about how much time I spend away from it. If you, too, accomplish your goals and derive fulfillment from your work and your life, neither should you.     

A potential link between dorsomedial hypothalamic nucleus NPY and energy balance

The function of dorsomedial hypothalamic neuropeptide Y (NPY) in energy balance has largely been restricted to lactation-induced hyperphagia. In this issue, Chao et?al. (2011) expand this role to include inhibition of both brown fat thermogenesis and conversion of white-to-brown adipocytes in a white fat depot, resulting in reduced energy expenditure.     

Autophagy in hypothalamic AgRP neurons regulates food intake and energy balance

Macroautophagy is a lysosomal degradative pathway that maintains cellular homeostasis by turning over cellular components. Here we demonstrate a role for autophagy in hypothalamic agouti-related peptide (AgRP) neurons in the regulation of food intake and energy balance. We show that starvation-induced hypothalamic autophagy mobilizes neuron-intrinsic lipids to generate endogenous free fatty acids, which in turn regulate AgRP levels. The functional consequences of inhibiting autophagy are the failure to upregulate AgRP in response to starvation, and constitutive increases in hypothalamic levels of pro-opiomelanocortin and its cleavage product α-melanocyte-stimulating hormone that typically contribute to a lean phenotype. We propose a conceptual framework for considering how autophagy-regulated lipid metabolism within hypothalamic neurons may modulate neuropeptide levels to have immediate effects on food intake, as well as long-term effects on energy homeostasis. Regulation of hypothalamic autophagy could become an effective intervention in conditions such as obesity and the metabolic syndrome.     

Role of hypothalamic orexin neurons in the regulation of arousal according to energy balance

Sleep and Biological Rhythms -     

Complementary lateral hypothalamic populations resist hunger pressure to balance nutritional and social needs

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BCL-2 in the crosshairs: tipping the balance of life and death

The discovery of B-cell lymphoma-2 (BCL-2) over 20 years ago revealed a new paradigm in cancer biology: the development and persistence of cancer can be driven by molecular roadblocks along the natural pathway to cell death. The subsequent identification of an expansive family of BCL-2 proteins provoked an intensive investigation of the interplay among these critical regulators of cell death. What emerged was a compelling tale of guardians and executioners, each participating in a molecular choreography that dictates cell fate. Ten years into the BCL-2 era, structural details defined how certain BCL-2 family proteins interact, and molecular targeting of the BCL-2 family has since become a pharmacological quest. Although many facets of BCL-2 family death signaling remain a mechanistic mystery, small molecules and peptides that effectively target BCL-2 are eliminating the roadblock to cell death, raising hopes for a medical breakthrough in cancer and other diseases of deregulated apoptosis.     

Neuropeptide exocytosis involving synaptotagmin-4 and oxytocin in hypothalamic programming of body weight and energy balance

Hypothalamic neuropeptides play essential roles in regulating energy and body weight balance. Energy imbalance and obesity have been linked to hypothalamic signaling defects in regulating neuropeptide genes; however, it is unknown whether dysregulation of neuropeptide exocytosis could be critically involved. This study discovered that synaptotagmin-4, an atypical modulator of synaptic exocytosis, is expressed most abundantly in oxytocin neurons of the hypothalamus. Synaptotagmin-4 negatively regulates oxytocin exocytosis, and dietary obesity is associated with increased vesicle binding of synaptotagmin-4 and thus enhanced negative regulation of oxytocin release. Overexpressing synaptotagmin-4 in hypothalamic oxytocin neurons and centrally antagonizing oxytocin in mice are similarly obesogenic. Synaptotagmin-4 inhibition prevents against dietary obesity by normalizing oxytocin release and energy balance under chronic nutritional excess. In conclusion, the negative regulation of synaptotagmin-4 on oxytocin release represents a hypothalamic basis of neuropeptide exocytosis in controlling obesity and related diseases.     

Leptin action through hypothalamic nitric oxide synthase-1-expressing neurons controls energy balance

Few effective measures exist to combat the worldwide obesity epidemic(1), and the identification of potential therapeutic targets requires a deeper understanding of the mechanisms that control energy balance. Leptin, an adipocyte-derived hormone that signals the long-term status of bodily energy stores, acts through multiple types of leptin receptor long isoform (LepRb)-expressing neurons (called here LepRb neurons) in the brain to control feeding, energy expenditure and endocrine function(2-4). The modest contributions to energy balance that are attributable to leptin action in many LepRb populations(5-9) suggest that other previously unidentified hypothalamic LepRb neurons have key roles in energy balance. Here we examine the role of LepRb in neuronal nitric oxide synthase (NOS1)-expressing LebRb (LepRb(NOS1)) neurons that comprise approximately 20% of the total hypothalamic LepRb neurons. Nos1(cre)-mediated genetic ablation of LepRb (Lepr(Nos1KO)) in mice produces hyperphagic obesity, decreased energy expenditure and hyperglycemia approaching that seen in whole-body LepRb-null mice. In contrast, the endocrine functions in Lepr(Nos1KO) mice are only modestly affected by the genetic ablation of LepRb in these neurons. Thus, hypothalamic LepRb(NOS1) neurons are a key site of action of the leptin-mediated control of systemic energy balance.     

Inputs and outputs of insulin receptor

The insulin receptor (IR) is an important hub in insulin signaling and its activation is tightly regulated. Upon insulin stimulation, IR is activated through autophosphorylation, and consequently phosphorylates several insulin receptor substrate (IRS) proteins, including IRS1-6, Shc and Gab1. Certain adipokines have also been found to activate IR. On the contrary, PTP, Grb and SOCS proteins, which are responsible for the negative regulation of IR, are characterized as IR inhibitors. Additionally, many other proteins have been identified as IR substrates and participate in the insulin signaling pathway. To provide a more comprehensive understanding of the signals mediated through IR, we reviewed the upstream and downstream signal molecules of IR, summarized the positive and negative modulators of IR, and discussed the IR substrates and interacting adaptor proteins. We propose that the molecular events associated with IR should be integrated to obtain a better understanding of the insulin signaling pathway and diabetes.     

Development of hypothalamic control over thyrotropin secretion during human prenatal life]

It was shown in the tissue culture experiments that the human hypophysis secreted autonomously the thyrotrophin during the last three fourths of the prenatal life. The intensity of secretion is the highest in the end of the first third of this period, then it decreases, but during the last third it increases reliably again. During the second half of development the level of thyrotrophin in female foetuses in reliably higher than in the male ones. In the beginning of the second third of prenatal life, the hypothalamic factors decrease the autonomous thyrotrophin secretion twice in foetuses of both the sexes. In the end of the second third, sexual differences appear in their effect; they decrease reliably the autonomous thyrotrophin secretion in the male foetuses, whereas no such effect is observed in the female ones. The stimulating effect of the hypothalamic thyrotrophin releasing hormone manifests itself during the last third of prenatal life in foetuses of both the sexes. During the second half of prenatal life, the thyrotrophin concentration in blood of female foetuses is also reliably higher than in male foetuses. There is a positive correlation in female foetuses between the thyrotrophin concentration in blood and the level of hypophysial secretion under the effect of hypothalamic factors. Thyrotrophin is found in the cranial fluid of foetuses. In some cases its concentration in the cranial fluid is higher than in the blood. No correlation was found between the levels of the hormone in fluid and blood in female foetuses; a positive correlation was found in male foteuses.     

Inputs and outputs for chromatin-targeted RNAi

Plant gene silencing is targeted to transposons and repeated sequences by small RNAs from the RNA interference (RNAi) pathway. Like classical RNAi, RNA-directed chromatin silencing involves the cleavage of double-stranded RNA by Dicer endonucleases to create small interfering RNAs (siRNAs), which bind to the Argonaute protein. The production of double-stranded RNA (dsRNA) must be carefully controlled to prevent inappropriate silencing. A plant-specific RNA polymerase IV (Pol IV) initiates siRNA production at silent heterochromatin, but Pol IV-independent mechanisms for making dsRNA also exist. Downstream of siRNA biogenesis, multiple chromatin marks might be targeted by Argonaute-siRNA complexes, yet mechanisms of chromatin modification remain poorly understood. Genomic studies of siRNA target loci promise to reveal novel biological functions for chromatin-targeted RNAi.