A Genetic Basis for Motivated Exercise

The persistence of stress-induced physical inactivity in rats: an investigation of central monoamine neurotransmitters and skeletal muscle oxidative stress

Introduction

Sedentary lifestyles have reached epidemic proportions world-wide. A growing body of literature suggests that exposures to adverse experiences (e.g., psychological traumas) are a significant risk factor for the development of physically inactive lifestyles. However, the biological mechanisms linking prior stress exposure and persistent deficits in physical activity engagement remains poorly understood.

Methods

The purpose of this study was twofold. First, to identify acute stress intensity thresholds that elicit long-term wheel running deficits in rats. To that end, young adult male rats were exposed to a single episode of 0, 50, or 100 uncontrollable tail shocks and then given free access to running wheels for 9 weeks. Second, to identify stress-induced changes to central monoamine neurotransmitters and peripheral muscle physiology that may be maladaptive to exercise output. For this study, rats were either exposed to a single episode of uncontrollable tail shocks (stress) or left undisturbed in home cages (unstressed). Eight days later, monoamine-related neurochemicals were quantified by ultra-high performance liquid chromatography (UHPLC) across brain reward, motor, and emotion structures immediately following a bout of graded treadmill exercise controlled for duration and intensity. Additionally, protein markers of oxidative stress, inflammation, and metabolic activity were assessed in the gastrocnemius muscle by Western blot.

Results

For experiment 1, stress exposure caused a shock number-dependent two to fourfold decrease in wheel running distance across the entire duration of the study. For experiment 2, stress exposure curbed an exercise-induced increase of dopamine (DA) turnover measures in the prefrontal cortex and hippocampus, and augmented serotonin (5HT) turnover in the hypothalamus and remaining cortical area. However, stress exposure also caused several monoaminergic changes independent of exercise that could underlie impaired motivation for physical activity, including a mild dopamine deficiency in the striatal area. Finally, stress potently increased HSP70 and lowered SOD2 protein concentrations in the gastrocnemius muscle, which may indicate prolonged oxidative stress.

Discussion

These data support some of the possible central and peripheral mechanisms by which exposure to adverse experiences may chronically impair physical activity engagement.

Regulation of Voluntary Physical Activity Behavior: A Review of Evidence Involving Dopaminergic Pathways in the Brain

Physical activity leads to well-established health benefits. Current efforts to enhance physical activity have targeted mainly socioeconomic factors. However, despite these efforts, only a small number of adults engage in regular physical activity to the point of meeting current recommendations. Evidence collected in rodent models and humans establish a strong central nervous system component that regulates physical activity behavior. In particular, dopaminergic pathways in the central nervous system are among the best-characterized biological mechanisms to date with respect to regulating reward, motivation, and habit formation, which are critical for establishing regular physical activity. Herein, we discuss evidence for a role of brain dopamine in the regulation of voluntary physical activity behavior based on selective breeding and pharmacological studies in rodents, as well as genetic studies in both rodents and humans. While these studies establish a role of dopamine and associated mechanisms in the brain in the regulation of voluntary physical activity behavior, there is clearly need for more research on the underlying biology involved in motivation for physical activity and the formation of a physical activity habit. Such knowledge at the basic science level may ultimately be translated into better strategies to enhance physical activity levels within the society.

Carving the senescent phenotype by the chemical reactivity of catecholamines: An integrative review

Macromolecules damaged by covalent modifications produced by chemically reactive metabolites accumulate in the slowly renewable components of living bodies and compromise their functions. Among such metabolites, catecholamines (CA) are unique, compared with the ubiquitous oxygen, ROS, glucose and methylglyoxal, in that their high chemical reactivity is confined to a limited set of cell types, including the dopaminergic and noradrenergic neurons and their direct targets, which suffer from CA propensities for autoxidation yielding toxic quinones, and for Pictet-Spengler reactions with carbonyl-containing compounds, which yield mitochondrial toxins. The functions progressively compromised because of that include motor performance, cognition, reward-driven behaviors, emotional tuning, and the neuroendocrine control of reproduction. The phenotypic manifestations of the resulting disorders culminate in such conditions as Parkinson's and Alzheimer's diseases, hypertension, sarcopenia, and menopause. The reasons to suspect that CA play some special role in aging accumulated since early 1970-ies. Published reviews address the role of CA hazardousness in the development of specific aging-associated diseases. The present integrative review explores how the bizarre discrepancy between CA hazardousness and biological importance could have emerged in evolution, how much does the chemical reactivity of CA contribute to the senescent phenotype in mammals, and what can be done with it.

Snord116 Post-transcriptionally Increases Nhlh2 mRNA Stability: Implications for Human Prader-Willi Syndrome

The smallest genomic region causing Prader-Willi Syndrome (PWS) deletes the non-coding RNA SNORD116 cluster; however, the function of SNORD116 remains a mystery. Previous work in the field revealed the tantalizing possibility that expression of NHLH2, a gene previously implicated in both obesity and hypogonadism, was downregulated in PWS patients and differentiated stem cells. In silico RNA: RNA modeling identified several potential interaction domains between SNORD116 and NHLH2 mRNA. One of these interaction domains was highly conserved in most vertebrate NHLH2 mRNAs examined. A construct containing the Nhlh2 mRNA, including its 3'-UTR, linked to a c-myc tag was transfected into a hypothalamic neuron cell line in the presence and absence of exogenously-expressed Snord116. Nhlh2 mRNA expression was upregulated in the presence of Snord116 dependent on the length and type of 3'UTR used on the construct. Furthermore, use of actinomycin D to stop new transcription in N29/2 cells demonstrated that the upregulation occurred through increased stability of the Nhlh2 mRNA in the 45 minutes immediately following transcription. In silico modeling also revealed that a single nucleotide variant (SNV) in the NHLH2 mRNA could reduce the predicted interaction strength of the NHLH2:SNORD116 diad. Indeed, use of an Nhlh2 mRNA construct containing this SNV significantly reduces the ability of Snord116 to increase Nhlh2 mRNA levels. For the first time, these data identify a motif and mechanism for SNORD116-mediated regulation of NHLH2, clarifying the mechanism by which deletion of the SNORD116 snoRNAs locus leads to PWS phenotypes.

Genetic variants related to physical activity or sedentary behaviour: a systematic review

BACKGROUND

Research shows that part of the variation in physical activity and sedentary behaviour may be explained by genetic factors. Identifying genetic variants associated with physical activity and sedentary behaviour can improve causal inference in physical activity research. The aim of this systematic review was to provide an updated overview of the evidence of genetic variants associated with physical activity or sedentary behaviour.

METHODS

We performed systematic literature searches in PubMed and Embase for studies published from 1990 to April 2020 using keywords relating to "physical activity", "exercise", "sedentariness" and "genetics". Physical activity phenotypes were either based on self-report (e.g., questionnaires, diaries) or objective measures (e.g., accelerometry, pedometer). We considered original studies aiming to i) identify new genetic variants associated with physical activity or sedentary behaviour (i.e., genome wide association studies [GWAS]), or ii) assess the association between known genetic variants and physical activity or sedentary behaviour (i.e., candidate gene studies). Study selection, data extraction, and critical appraisal were carried out by independent researchers, and risk of bias and methodological quality was assessed for all included studies.

RESULTS

Fifty-four out of 5420 identified records met the inclusion criteria. Six of the included studies were GWAS, whereas 48 used a candidate gene approach. Only one GWAS and three candidate gene studies were considered high-quality. The six GWAS discovered up to 10 single nucleotide polymorphisms (SNPs) associated with physical activity or sedentariness that reached genome-wide significance. In total, the candidate gene studies reported 30 different genes that were associated (p < 0.05) with physical activity or sedentary behaviour. SNPs in or close to nine candidate genes were associated with physical activity or sedentary behaviour in more than one study.

CONCLUSION

GWAS have reported up to 10 loci associated with physical activity or sedentary behaviour. Candidate gene studies have pointed to some interesting genetic variants, but few have been replicated. Our review highlights the need for high-quality GWAS in large population-based samples, and with objectively assessed phenotypes, in order to establish robust genetic instruments for physical activity and sedentary behaviour. Furthermore, consistent replications in GWAS are needed to improve credibility of genetic variants.

TRIAL REGISTRATION

Prospero CRD42019119456 .

Natural Selection at the NHLH2 Core Promoter Exceptionally Long CA-Repeat in Human and Disease-Only Genotypes in Late-Onset Neurocognitive Disorder

BACKGROUND

Approximately 2% of the human core promoter short tandem repeats (STRs) reach lengths of ≥6 repeats, which may in part be a result of adaptive evolutionary processes and natural selection. A single-exon transcript of the human nescient helix loop helix 2 (NHLH2) gene is flanked by the longest CA-repeat detected in a human protein-coding gene core promoter (Ensembl transcript ID: ENST00000369506.1). NHLH2 is involved in several biological and pathological pathways, such as motivated exercise, obesity, and diabetes.

METHODS

The allele and genotype distribution of the NHLH2 CA-repeat were investigated by sequencing in 655 Iranian subjects, consisting of late-onset neurocognitive disorder (NCD) as a clinical entity (n = 290) and matched controls (n = 365). The evolutionary trend of the CA-repeat was also studied across vertebrates.

RESULTS

The allele range was between 9 and 25 repeats in the NCD cases, and 12 and 24 repeats in the controls. At the frequency of 0.56, the 21-repeat allele was the predominant allele in the controls. While the 21-repeat was also the predominant allele in the NCD patients, we detected significant decline of the frequency (p < 0.0001) and homozygosity (p < 0.006) of this allele in this group. Furthermore, 12 genotypes were detected across 16 patients (5.5% of the entire NCD sample) and not in the controls (disease-only genotypes; p < 0.0003), consisting of at least one extreme allele. The extreme alleles were at 9, 12, 13, 18, and 19 repeats (extreme short end), and 23, 24, and 25 repeats (extreme long end), and their frequencies ranged between 0.001 and 0.04. The frequency of the 21-repeat allele significantly dropped to 0.09 in the disease-only genotype compartment (p < 0.0001). Evolutionarily, while the maximum length of the NHLH2 CA-repeat was 11 repeats in non-primates, this CA-repeat was ≥14 repeats in primates and reached maximum length in human.

CONCLUSION

We propose a novel locus for late-onset NCD at the NHLH2 core promoter exceptionally long CA-STR and natural selection at this locus. Furthermore, there was indication of genotypes at this locus that unambiguously linked to late-onset NCD. This is the first instance of natural selection in favor of a predominantly abundant STR allele in human and its differential distribution in late-onset NCD.

Distribution of allele frequencies for genes associated with physical activity and/or physical capacity in a homogenous Norwegian cohort- a cross-sectional study

BACKGROUND

There are large individual differences in physical activity (PA) behavior as well as trainability of physical capacity. Heritability studies have shown that genes may have as much impact on exercise participation behavior as environmental factors. Genes that favor both trainability and participation may increase the levels of PA. The present study aimed to assess the allele frequencies in genes associated with PA and/or physical capacity, and to see if there is any association between these polymorphisms and self-reported PA levels in a cohort of middle-aged Norwegians of Scandinavian descent (n = 831; mean age mean age (± SD) 55.5 ± 3.8 years).

RESULTS

The genotype distributions of the ACTN3 R577X, ACE I/D and MAOA uVNTR polymorphisms were similar to other populations of European descent. When comparing the genotype distribution between the low/medium level PA group (LMPA) and high level PA groups (HPA), a significant difference in ACTN3 577X allele distribution was found. The X allele frequency was 10% lower in the HPA level group (P = 0.006). There were no differences in the genotype distribution of the ACE I/D or MAOA uVNTR polymorphism. Education and previous participation in sports or outdoor activities was positively associated with the self-reported PA levels (P ≤ 0.001).

CONCLUSIONS

To the best of our knowledge, this is the first study to report association between ACTN3 R577X genotype and PA level in middle-aged Scandinavians. Nevertheless, the contribution of a single polymorphism to a complex trait, like PA level, is likely small. Socioeconomic variables, as education and previous participation in sports or outdoor activities, are positively associated with the self-reported PA levels.

The Transcriptional Signature of a Runner's High

INTRODUCTION

Endorphins, endocannabinoids, monoamines, and neurotrophins have all been implicated in the euphoric response to endurance running, known as a runner's high (RH). The epitranscriptional mechanisms regulating this effect have not been defined. Here, we investigate peripheral micro-ribonucleic acid (miRNA) changes unique to athletes experiencing postrun euphoria, yielding insights into gene networks that control an RH.

METHODS

A cohort study involving 25 collegiate runners (48% females, age = 20 ± 1 yr) examined salivary RNA levels before and after a long-distance run. Participants were divided into RH and nonrunner's high (NRH) groups based on surveys of four criteria (mood, lost sense of time, run quality, and euphoria). Physiological measures were also recorded (temperature, heart rate, blood pressure, pupillary dilatation, and salivary serotonin). Levels of miRNAs and their messenger RNA targets were compared across pre- and postrun samples from RH and NRH groups with two-way ANOVA. Representation of opioid, gamma-aminobutyic acid (GABA), endocannabinoid, neurotrophin, serotonergic, and dopaminergic pathways was assessed in DIANA miRPath. Pearson's correlation analyses examined relationships between miRNAs and RH indices.

RESULTS

RH participants (n = 13) demonstrated postrun mydriasis (P = 0.046) and hypothermia (P = 0.043) relative to NRH participants (n = 12) but had no difference in serotonin dynamics (P = 0.88). Six miRNAs (miR-194-5p, miR-4676-3p, miR-4254, miR-4425, miR-1273-3p, miR-6743-5p) exhibited significant effects (false discovery rate P value < 0.05) across pre- or postrun and RH/NRH groups. These miRNAs displayed target enrichment for opioid (P = 2.74E-06) and GABA (P = 0.00016) pathways. miR-1237-3p levels were related with lost sense of time (R = 0.40). Mitogen-activated protein kinase (MAPK11), an endocannabinoid target of miR-1273-3p, was nominally elevated in RH participants (false discovery rate P value = 0.11).

CONCLUSIONS

Unique dynamics in miRNA concentration occur in athletes with subjective/objective evidence of RH, targeting genes implicated endorphin, endocannabinoid, and GABAergic signaling.

The effect of monoamines reuptake inhibitors on aerobic exercise performance in bank voles from a selection experiment

Exercise performance depends on both physiological abilities (e.g., muscle strength) and behavioral characteristics (e.g., motivation). We tested the hypothesis that evolution of increased aerobic exercise performance can be facilitated by evolution of neuropsychological mechanisms responsible for motivation to undertake physical activity. We used a unique model system: lines of bank voles Myodes glareolus selected for high swim-induced aerobic metabolism ("aerobic" A lines). In generation 21, voles from the 4 A lines achieved a 57% higher "voluntary maximum" swim-induced aerobic metabolism (VO2swim) than voles from 4 unselected, "control" C lines. In C lines, VO2swim was 9% lower than the maximum forced-exercise aerobic metabolism (VO2run; P = 0.007), while in A lines it was even higher than VO2run, although not significantly (4%, P = 0.15). Thus, we hypothesized that selection changed both the aerobic capacity and the neuronal mechanisms behind motivation to undertake activity. We investigated the influence of reuptake inhibitors of dopamine (DARI), serotonin (SSRI), and norepinephrine (NERI) on VO2swim. The drugs decreased VO2swim both in C and A lines (% decrease compared with saline: DARI 8%, P < 0.001; SSRI 6%, P < 0.001; NERI 8%, P < 0.001), but the proportional response differed between selection directions only for NERI (stronger effect in C lines: P = 0.008) and the difference was marginally non-significant for SSRI (P = 0.07) and DARI (P = 0.06). Thus, the results suggest that all the 3 monoamines are involved in signaling pathways controlling the motivation to be active and that norepinephrine could have played a role in the evolution of increased aerobic exercise performance in our animal model.

Biocultural approach of the association between maturity and physical activity in youth

OBJECTIVE

To test the biocultural model through direct and indirect associations between biological maturation, adiposity, cardiorespiratory fitness, feelings of sadness, social relationships, and physical activity in adolescents.

METHODS

This was a cross-sectional study conducted with 1,152 Brazilian adolescents aged between 10 and 17 years. Somatic maturation was estimated through Mirwald's method (peak height velocity). Physical activity was assessed through Baecke questionnaire (occupational, leisure, and sport contexts). Body mass index, body fat (sum of skinfolds), cardiorespiratory fitness (20-m shuttle run test), self-perceptions of social relationship, and frequency of sadness feelings were obtained for statistical modeling.

RESULTS

Somatic maturation is directly related to sport practice and leisure time physical activity only among girls (β=0.12, p<0.05 and β=0.09, respectively, p<0.05). Moreover, biological (adiposity and cardiorespiratory fitness), psychological (sadness), and social (satisfaction with social relationships) variables mediated the association between maturity and physical activity in boys and for occupational physical activity in girls. In general, models presented good fit coefficients.

CONCLUSION

Biocultural model presents good fit and emotional/biological factors mediate part of the relationship between somatic maturation and physical activity.

Revisiting the evolutionary origins of obesity: lazy versus peppy-thrifty genotype hypothesis

The recent global obesity epidemic is attributed to major societal and environmental changes, such as excessive energy intake and sedentary lifestyle. However, exposure to 'obesogenic' environments does not necessarily result in obesity at the individual level, as 40-75% of body mass index variation in population is attributed to genetic differences. The thrifty genotype theory posits that genetic variants promoting efficient food sequestering and optimal deposition of fat during periods of food abundance were evolutionarily advantageous for the early hunter-gatherer and were positively selected. However, the thrifty genotype is likely too simplistic and fails to provide a justification for the complex distribution of obesity predisposing gene variants and for the broad range of body mass index observed in diverse ethnic groups. This review proposes that gene pleiotropy may better account for the variability in the distribution of obesity susceptibility alleles across modern populations. We outline the lazy-thrifty versus peppy-thrifty genotype hypothesis and detail the body of evidence in the literature in support of this novel concept. Future population genetics and mathematical modelling studies that account for pleiotropy may further improve our understanding of the evolutionary origins of the current obesity epidemic.

Dopaminergic Genetic Variants and Voluntary Externally Paced Exercise Behavior

PURPOSE

Most candidate gene studies on the neurobiology of voluntary exercise behavior have focused on the dopaminergic signaling pathway and its role in the mesolimbic reward system. We hypothesized that dopaminergic candidate genes may influence exercise behavior through additional effects on executive functioning and that these effects are only detected when the types of exercise activity are taken into account.

METHODS

Data on voluntary exercise behavior and at least one single-nucleotide polymorphism/variable number of tandem repeat (VNTR) were available for 12,929 participants of the Netherlands Twin Registry. Exercise activity was classified as externally paced if a high level of executive function skill was required. The total volume of voluntary exercise (minutes per week) as well as the volume specifically spent on externally paced activities were tested for association with nine functional dopaminergic polymorphisms (DRD1: rs265981, DRD2/ANKK1: rs1800497, DRD3: rs6280, DRD4: VNTR 48 bp, DRD5: VNTR 130-166 bp, DBH: rs2519152, DAT1: VNTR 40 bp, COMT: rs4680, MAOA: VNTR 30 bp), a polygenic score (PGS) based on nine alleles leading to lower dopamine responsiveness, and a PGS based on three alleles associated with both higher reward sensitivity and better executive functioning (DRD2/ANKK1: "G" allele, COMT: Met allele, DAT1: 440-bp allele).

RESULTS

No association with total exercise volume or externally paced exercise volume was found for individual alleles or the nine-allele PGS. The volume of externally paced exercise behavior was significantly associated with the reward and executive function congruent PGS. This association was driven by the DAT1 440-bp and COMT Met allele, which acted as increaser alleles for externally paced exercise behavior.

CONCLUSIONS

Taking into account the types of exercise activity may increase the success of identifying genetic variants and unraveling the neurobiology of voluntary exercise behavior.

The Genetics of Physical Activity

PURPOSE OF REVIEW

Physical activity (PA) is a well-established modifiable lifestyle determinant for multiple cardio-metabolic outcomes. While many psychosocial and environmental correlates of PA have been identified, current understanding of the genetic architecture that contributes to PA is still very limited, especially when compared to other phenotypes such as obesity and diabetes.

RECENT FINDINGS

This review systematically and comprehensively assesses available evidence from animal experiments, family studies, population-based candidate gene analyses, and genome-wide association studies (GWAS) studying the genetics of physical activity patterns. It discusses the scientific evolution in the field of PA genetics, including the recognition of increased sample sizes, the shift from early family-based approaches to association-based design, and the rapidly advancement of enabling genotyping and sequencing technologies. In addition, this review points to the gaps in the current knowledge base, including the general lack of GWAS and whole-genome sequence analyses particularly understudied populations, and the need for large-scale collaborative effort in both observational and experimental settings. In this review, we also call for research utilizing systems biology strategies for PA genetic research and accounting for complex gene-environment interactions that may vary by race/ethnicity. The epidemic of physical inactivity has been a public health nemesis, encompassing a large burden of diseases and high societal costs. A better understanding of the genetic basis of PA can inform public health policies for the prevention, control, and treatment of many chronic diseases related to physical inactivity.

Maternal gestational weight gain and objectively measured physical activity among offspring

Objective

Animal studies have suggested that maternal weight-related factors during pregnancy can program offspring physical activity in a sex-dependent manner. However, there is limited evidence in humans. The purpose of this study was to investigate the association between maternal gestational weight gain (GWG) and offspring total physical activity (TPA) level and to determine whether these associations are moderated by sex of offspring or maternal pre-pregnancy weight status.

Method

We studied 56 boys (mean age = 3.7 years, standard deviation (SD) 0.5) and 57 girls (mean age = 3.5±0.5 years) enrolled in licensed childcare centers. TPA was objectively measured using Actical^® accelerometers. Information on pre-pregnancy body mass index (BMI), GWG, and other maternal factors were collected with a maternal health questionnaire. Associations between GWG, as a continuous variable or categorically (inadequate, adequate, and excessive), and offspring TPA were analysed using linear mixed models to take into account the intraclass correlation between the clusters (childcare centers). Models were adjusted for gestational age, accelerometer weartime, socioeconomic status, and pre-pregnancy BMI status.

Results

We found a significant sex interaction (P-value = 0.009). In boys, greater GWG was associated with decreased offspring TPA (β = -3.2 counts⋅1000⁻¹/d, 95% confidence intervals (CI) = -6.4–0.02, P-value = 0.049). In girls born to mothers categorized as overweight or obese, the association between the GWG and TPA followed an inverted U-shape curve (β for GWG squared = -0.1 counts⋅1000⁻¹/d, 95% CI = (-0.2 –-0.04), P-value = 0.005). In contrast, a U-shaped curve was found in girls born to mothers classified as lean (pre-pregnancy BMI<25 kg/m²) (β for GWG squared = 0.7 counts⋅1000⁻¹/d, 95% CI = 0.2–1.2, P-value = 0.011). In boys, TPA in offspring was higher among women with inadequate GWG compared to adequate GWG (P-value = 0.0137), whereas no significant differences were found in girls (P-value = 0.107).

Conclusion

Maternal GWG can be an important biological marker of offspring TPA. These findings support the sex-dependent early developmental programming influence of GWG on TPA.

A new aspect of chronic pain as a lifestyle-related disease

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Activation of mesolimbic dopamine system underlies exercise-induced hypoalgesia.

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Interaction between mesolimbic system and hypothalamus determines physical activity.

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Changing the lifestyle inactive to active may attenuate and prevent chronic pain.

Physical exercise has been established as a low-cost, safe, and effective way to manage chronic intractable pain. We investigated the underlying mechanisms of exercise-induced hypoalgesia (EIH) using a mouse model of neuropathic pain (NPP). Epigenetic changes in activated microglia and maintained GABA synthesis in the spinal dorsal horn may contribute to EIH. Voluntary exercise (VE), a strong reward for animals, also induced EIH, which may be due in part to the activation of dopamine (DA) neurons in the ventral tegmental area (VTA). VE increases the expression of pCREB in dopaminergic neurons in the VTA, which would enhance dopamine production, and thereby contributes to the activation of the mesolimbic reward system in NPP model mice. We demonstrated that neurons in the laterodorsal tegmental and pedunculopontine tegmental nuclei, a major input source of rewarding stimuli to the VTA, were activated by exercise.

Chronic pain is at least partly attributed to sedentary and inactive lifestyle as indicated by the Fear-avoidance model. Therefore, chronic pain could be recognized as a lifestyle-related disease. Physical activity/inactivity may be determined by genetic/epigenetic and neural factors encoded in our brain. The hypothalamus and reward system is closely related in the axis of food intake, energy metabolism and physical activity. Understanding the interactions between the mesolimbic DA system and the hypothalamus that sense and regulate energy balance is thus of significant importance. For example, proopiomelanocortin neurons and melanocortin 4 receptors may play a role in connecting these two systems. Therefore, in a certain sense, chronic pain and obesity may share common behavioral and neural pathology, i.e. physical inactivity, as a result of inactivation of the mesolimbic DA system. Exercise and increasing physical activity in daily life may be important in treating and preventing chronic pain, a life-style related disease.

The metabolic sensor Sirt1 and the hypothalamus: Interplay between peptide hormones and pro-hormone convertases

The last decade had witnessed a tremendous progress in our understanding of the causes of metabolic diseases including obesity. Among the contributing factors regulating energy balance are nutrient sensors such as sirtuins. Sirtuin1 (Sirt1), a NAD + - dependent deacetylase is affected by diet, environmental stress, and also plays a critical role in metabolic health by deacetylating proteins in many tissues, including liver, muscle, adipose tissue, heart, endothelium, and in the complexity of the hypothalamus. Because of its dependence on NAD+, Sirt1 also functions as a nutrient/redox sensor, and new novel data show a function of this enzyme in the maturation of hypothalamic peptide hormones controlling energy balance either through regulation of specific nuclear transcription factors or by regulating specific pro-hormone convertases (PCs) involved in the post-translational processing of pro-hormones. The post-translational processing mechanism of pro-hormones is critical in the pathogenesis of obesity as recently shown that metabolic and physiological triggers affect the biosynthesis and processing of many peptides hormones. Specific regulation of pro-hormone processing is likely another key step where final amounts of bioactive peptides can be tightly regulated. Different factors stimulate or inhibit pro-hormones biosynthesis in concert with an increase in the PCs involved in the maturation of bioactive hormones. Adding more complexity to the system, the new studies describe here suggest that Sirt1 could also regulate the fate of peptide hormone biosynthesis. The present review summarizes the recent progress in hypothalamic SIRT1 research with a particular emphasis on the tissue-specific control of neuropeptide hormone maturation. The series of studies done in mouse and rat models strongly advocate for the first time that a deacetylating enzyme could be a regulator in the maturation of peptide hormones and their processing enzymes. These discoveries are the culmination of the first in-depth understanding of the metabolic role of Sirt1 in the brain. It suggests that Sirt1 behaves differently in the brain than in organs such as the liver and pancreas, where the enzyme has been more commonly studied.