Obesity-programmed mice are rescued by early genetic intervention

Obesity is a chronic metabolic disorder affecting half a billion people worldwide. Major difficulties in managing obesity are the cessation of continued weight loss in patients after an initial period of responsiveness and rebound to pretreatment weight. It is conceivable that chronic weight gain unrelated to physiological needs induces an allostatic regulatory state that defends a supranormal adipose mass despite its maladaptive consequences. To challenge this hypothesis, we generated a reversible genetic mouse model of early-onset hyperphagia and severe obesity by selectively blocking the expression of the proopiomelanocortin gene (Pomc) in hypothalamic neurons. Eutopic reactivation of central POMC transmission at different stages of overweight progression normalized or greatly reduced food intake in these obesity-programmed mice. Hypothalamic Pomc rescue also attenuated comorbidities such as hyperglycemia, hyperinsulinemia, and hepatic steatosis and normalized locomotor activity. However, effectiveness of treatment to normalize body weight and adiposity declined progressively as the level of obesity at the time of Pomc induction increased. Thus, our study using a novel reversible monogenic obesity model reveals the critical importance of early intervention for the prevention of subsequent allostatic overload that auto-perpetuates obesity.     

Serotonin 2C receptors in pro-opiomelanocortin neurons regulate energy and glucose homeostasis

Energy and glucose homeostasis are regulated by central serotonin 2C receptors. These receptors are attractive pharmacological targets for the treatment of obesity; however, the identity of the serotonin 2C receptor–expressing neurons that mediate the effects of serotonin and serotonin 2C receptor agonists on energy and glucose homeostasis are unknown. Here, we show that mice lacking serotonin 2C receptors (Htr2c) specifically in pro-opiomelanocortin (POMC) neurons had normal body weight but developed glucoregulatory defects including hyperinsulinemia, hyperglucagonemia, hyperglycemia, and insulin resistance. Moreover, these mice did not show anorectic responses to serotonergic agents that suppress appetite and developed hyperphagia and obesity when they were fed a high-fat/high-sugar diet. A requirement of serotonin 2C receptors in POMC neurons for the maintenance of normal energy and glucose homeostasis was further demonstrated when Htr2c loss was induced in POMC neurons in adult mice using a tamoxifen-inducible POMC-cre system. These data demonstrate that serotonin 2C receptor–expressing POMC neurons are required to control energy and glucose homeostasis and implicate POMC neurons as the target for the effect of serotonin 2C receptor agonists on weight-loss induction and improved glycemic control.     

Melanism in Peromyscus Is Caused by Independent Mutations in Agouti

Identifying the molecular basis of phenotypes that have evolved independently can provide insight into the ways genetic and developmental constraints influence the maintenance of phenotypic diversity. Melanic (darkly pigmented) phenotypes in mammals provide a potent system in which to study the genetic basis of naturally occurring mutant phenotypes because melanism occurs in many mammals, and the mammalian pigmentation pathway is well understood. Spontaneous alleles of a few key pigmentation loci are known to cause melanism in domestic or laboratory populations of mammals, but in natural populations, mutations at one gene, the melanocortin-1 receptor (Mc1r), have been implicated in the vast majority of cases, possibly due to its minimal pleiotropic effects. To investigate whether mutations in this or other genes cause melanism in the wild, we investigated the genetic basis of melanism in the rodent genus Peromyscus, in which melanic mice have been reported in several populations. We focused on two genes known to cause melanism in other taxa, Mc1r and its antagonist, the agouti signaling protein (Agouti). While variation in the Mc1r coding region does not correlate with melanism in any population, in a New Hampshire population, we find that a 125-kb deletion, which includes the upstream regulatory region and exons 1 and 2 of Agouti, results in a loss of Agouti expression and is perfectly associated with melanic color. In a second population from Alaska, we find that a premature stop codon in exon 3 of Agouti is associated with a similar melanic phenotype. These results show that melanism has evolved independently in these populations through mutations in the same gene, and suggest that melanism produced by mutations in genes other than Mc1r may be more common than previously thought.     

Disruption of hypothalamic leptin signaling in mice leads to early-onset obesity,but physiological adaptations in mature animals stabilize adiposity levels

Distinct populations of leptin-sensing neurons in the hypothalamus, midbrain, and brainstem contribute to the regulation of energy homeostasis. To assess the requirement for leptin signaling in the hypothalamus, we crossed mice with a floxed leptin receptor allele (Lepr^fl) to mice transgenic for Nkx2.1-Cre, which drives Cre expression in the hypothalamus and not in more caudal brain regions, generating Lepr^Nkx2.1KO mice. From weaning, Lepr^Nkx2.1KO mice exhibited phenotypes similar to those observed in mice with global loss of leptin signaling (Lepr^db/db mice), including increased weight gain and adiposity, hyperphagia, cold intolerance, and insulin resistance. However, after 8 weeks of age, Lepr^Nkx2.1KO mice maintained stable adiposity levels, whereas the body fat percentage of Lepr^db/db animals continued to escalate. The divergence in the adiposity phenotypes of Lepr^db/db and Lepr^Nkx2.1KO mice with age was concomitant with increased rates of linear growth and energy expenditure in Lepr^Nkx2.1KO mice. These data suggest that remaining leptin signals in Lepr^Nkx2.1KO mice mediate physiological adaptations that prevent the escalation of the adiposity phenotype in adult mice. The persistence of severe adiposity in Lepr^Nkx2.1KO mice, however, suggests that compensatory actions of circuits regulating growth and energy expenditure are not sufficient to reverse obesity established at an early age.     

Melanocortin 4 receptor stimulation prevents antidepressant-associated weight gain in mice caused by long-term fluoxetine exposure

Contrasting with the predicted anorexigenic effect of increasing brain serotonin signaling, long-term use of selective serotonin reuptake inhibitor (SSRI) antidepressants correlates with body weight (BW) gain. This adverse outcome increases the risk of transitioning to obesity and interferes with treatment compliance. Here, we show that orally administered fluoxetine (Flx), a widely prescribed SSRI, increased BW by enhancing food intake in healthy mice at 2 different time points and through 2 distinct mechanisms. Within hours, Flx decreased the activity of a subset of brainstem serotonergic neurons by triggering autoinhibitory signaling through 5-hydroxytryptamine receptor 1a (Htr1a). Following a longer treatment period, Flx blunted 5-hydroxytryptamine receptor 2c (Htr2c) expression and signaling, decreased the phosphorylation of cAMP response element–binding protein (CREB) and STAT3, and dampened the production of pro-opiomelanocortin (POMC, the precursor of α-melanocyte stimulating hormone [α-MSH]) in hypothalamic neurons, thereby increasing food intake. Accordingly, exogenous stimulation of the melanocortin 4 receptor (Mc4r) by cotreating mice with Flx and lipocalin 2, an anorexigenic hormone signaling through this receptor, normalized feeding and BW. Flx and other SSRIs also inhibited CREB and STAT3 phosphorylation in a human neuronal cell line, suggesting that these noncanonical effects could also occur in individuals treated long term with SSRIs. By defining the molecular basis of long-term SSRI–associated weight gain, we propose a therapeutic strategy to counter this effect.     

Estrogen receptor–α in medial amygdala neurons regulates body weight

Estrogen receptor–α (ERα) activity in the brain prevents obesity in both males and females. However, the ERα-expressing neural populations that regulate body weight remain to be fully elucidated. Here we showed that single-minded–1 (SIM1) neurons in the medial amygdala (MeA) express abundant levels of ERα. Specific deletion of the gene encoding ERα (Esr1) from SIM1 neurons, which are mostly within the MeA, caused hypoactivity and obesity in both male and female mice fed with regular chow, increased susceptibility to diet-induced obesity (DIO) in males but not in females, and blunted the body weight–lowering effects of a glucagon-like peptide-1–estrogen (GLP-1–estrogen) conjugate. Furthermore, selective adeno-associated virus-mediated deletion of Esr1 in the MeA of adult male mice produced a rapid body weight gain that was associated with remarkable reductions in physical activity but did not alter food intake. Conversely, overexpression of ERα in the MeA markedly reduced the severity of DIO in male mice. Finally, an ERα agonist depolarized MeA SIM1 neurons and increased their firing rate, and designer receptors exclusively activated by designer drug–mediated (DREADD-mediated) activation of these neurons increased physical activity in mice. Collectively, our results support a model where ERα signals activate MeA neurons to stimulate physical activity, which in turn prevents body weight gain.     

Infant Body Composition and Adipokine Concentrations in Relation to Maternal Gestational Weight Gain

OBJECTIVE

To investigate associations of maternal gestational weight gain and body composition and their impact on offspring body composition and adipocytokine, glucose, and insulin concentrations at age 4 months.

RESEARCH DESIGN AND METHODS

This was a prospective study including 31 mother-infant pairs (N = 62). Maternal body composition was assessed using doubly labeled water. Infant body composition was assessed at 4 months using air displacement plethysmography, and venous blood was assayed for glucose, insulin, adiponectin, interleukin-6 (IL-6), and leptin concentrations.

RESULTS

Rate of gestational weight gain in midpregnancy was significantly associated with infant fat mass (r = 0.41, P = 0.03); rate of gestational weight in late pregnancy was significantly associated with infant fat-free mass (r = 0.37, P = 0.04). Infant birth weight was also strongly correlated with infant fat-free mass at 4 months (r = 0.63, P = 0.0002). Maternal BMI and maternal fat mass were strongly inversely associated with infant IL-6 concentrations (r = −0.60, P = 0.002 and r = −0.52, P = 0.01, respectively). Infant fat-free mass was inversely related to infant adiponectin concentrations (r = −0.48, P = 0.008) and positively correlated with infant blood glucose adjusted for insulin concentrations (r = 0.42, P = 0.04). No significant associations for leptin were observed.

CONCLUSIONS

Timing of maternal weight gain differentially impacts body composition of the 4-month-old infant, which in turn appears to affect the infant’s glucose and adipokine concentrations.     

Impaired kisspeptin signaling decreases metabolism and promotes glucose intolerance and obesity

The neuropeptide kisspeptin regulates reproduction by stimulating gonadotropin-releasing hormone (GnRH) neurons via the kisspeptin receptor KISS1R. In addition to GnRH neurons, KISS1R is expressed in other brain areas and peripheral tissues, which suggests that kisspeptin has additional functions beyond reproduction. Here, we studied the energetic and metabolic phenotype in mice lacking kisspeptin signaling (Kiss1r KO mice). Compared with WT littermates, adult Kiss1r KO females displayed dramatically higher BW, leptin levels, and adiposity, along with strikingly impaired glucose tolerance. Conversely, male Kiss1r KO mice had normal BW and glucose regulation. Surprisingly, despite their obesity, Kiss1r KO females ate less than WT females; however, Kiss1r KO females displayed markedly reduced locomotor activity, respiratory rate, and energy expenditure, which were not due to impaired thyroid hormone secretion. The BW and metabolic phenotype in Kiss1r KO females was not solely reflective of absent gonadal estrogen, as chronically ovariectomized Kiss1r KO females developed obesity, hyperleptinemia, reduced metabolism, and glucose intolerance compared with ovariectomized WT females. Our findings demonstrate that in addition to reproduction, kisspeptin signaling influences BW, energy expenditure, and glucose homeostasis in a sexually dimorphic and partially sex steroid–independent manner; therefore, alterations in kisspeptin signaling might contribute, directly or indirectly, to some facets of human obesity, diabetes, or metabolic dysfunction.     

PTP1B and SHP2 in POMC neurons reciprocally regulate energy balance in mice

Protein tyrosine phosphatase 1B (PTP1B) and SH2 domain–containing protein tyrosine phosphatase–2 (SHP2) have been shown in mice to regulate metabolism via the central nervous system, but the specific neurons mediating these effects are unknown. Here, we have shown that proopiomelanocortin (POMC) neuron–specific deficiency in PTP1B or SHP2 in mice results in reciprocal effects on weight gain, adiposity, and energy balance induced by high-fat diet. Mice with POMC neuron–specific deletion of the gene encoding PTP1B (referred to herein as POMC-Ptp1b^–/– mice) had reduced adiposity, improved leptin sensitivity, and increased energy expenditure compared with wild-type mice, whereas mice with POMC neuron–specific deletion of the gene encoding SHP2 (referred to herein as POMC-Shp2^–/– mice) had elevated adiposity, decreased leptin sensitivity, and reduced energy expenditure. POMC-Ptp1b^–/– mice showed substantially improved glucose homeostasis on a high-fat diet, and hyperinsulinemic-euglycemic clamp studies revealed that insulin sensitivity in these mice was improved on a standard chow diet in the absence of any weight difference. In contrast, POMC-Shp2^–/– mice displayed impaired glucose tolerance only secondary to their increased weight gain. Interestingly, hypothalamic Pomc mRNA and α–melanocyte-stimulating hormone (αMSH) peptide levels were markedly reduced in POMC-Shp2^–/– mice. These studies implicate PTP1B and SHP2 as important components of POMC neuron regulation of energy balance and point to what we believe to be a novel role for SHP2 in the normal function of the melanocortin system.     

Progranulin deficiency promotes neuroinflammation and neuron loss following toxin-induced injury

Progranulin (PGRN) is a widely expressed secreted protein that is linked to inflammation. In humans, PGRN haploinsufficiency is a major inherited cause of frontotemporal dementia (FTD), but how PGRN deficiency causes neurodegeneration is unknown. Here we show that loss of PGRN results in increased neuron loss in response to injury in the CNS. When exposed acutely to 1-methyl-4-(2′-methylphenyl)-1,2,3,6-tetrahydrophine (MPTP), mice lacking PGRN (Grn^–/–) showed more neuron loss and increased microgliosis compared with wild-type mice. The exacerbated neuron loss was due not to selective vulnerability of Grn^–/– neurons to MPTP, but rather to an increased microglial inflammatory response. Consistent with this, conditional mutants lacking PGRN in microglia exhibited MPTP-induced phenotypes similar to Grn^–/– mice. Selective depletion of PGRN from microglia in mixed cortical cultures resulted in increased death of wild-type neurons in the absence of injury. Furthermore, Grn^–/– microglia treated with LPS/IFN-γ exhibited an amplified inflammatory response, and conditioned media from these microglia promoted death of cultured neurons. Our results indicate that PGRN deficiency leads to dysregulated microglial activation and thereby contributes to increased neuron loss with injury. These findings suggest that PGRN deficiency may cause increased neuron loss in other forms of CNS injury accompanied by neuroinflammation.     

Ventromedial hypothalamus–specific Ptpn1 deletion exacerbates diet-induced obesity in female mice

Protein-tyrosine phosphatase 1B (PTP1B) regulates food intake (FI) and energy expenditure (EE) by inhibiting leptin signaling in the hypothalamus. In peripheral tissues, PTP1B regulates insulin signaling, but its effects on CNS insulin action are largely unknown. Mice harboring a whole-brain deletion of the gene encoding PTP1B (Ptpn1) are lean, leptin-hypersensitive, and resistant to high fat diet–induced (HFD-induced) obesity. Arcuate proopiomelanocortin (POMC) neuron–specific deletion of Ptpn1 causes a similar, but much milder, phenotype, suggesting that PTP1B also acts in other neurons to regulate metabolism. Steroidogenic factor-1–expressing (SF-1–expressing) neurons in the ventromedial hypothalamus (VMH) play an important role in regulating body weight, FI, and EE. Surprisingly, Ptpn1 deletion in SF-1 neurons caused an age-dependent increase in adiposity in HFD-fed female mice. Although leptin sensitivity was increased and FI was reduced in these mice, they had impaired sympathetic output and decreased EE. Immunohistochemical analysis showed enhanced leptin and insulin signaling in VMH neurons from mice lacking PTP1B in SF-1 neurons. Thus, in the VMH, leptin negatively regulates FI, promoting weight loss, whereas insulin suppresses EE, leading to weight gain. Our results establish a novel role for PTP1B in regulating insulin action in the VMH and suggest that increased insulin responsiveness in SF-1 neurons can overcome leptin hypersensitivity and enhance adiposity.     

Choice of atypical antipsychotic therapy for patients with schizophrenia: An analysis of a medicaid population

Background:

In patients treated at Veterans Affairs facilities, demographicand clinical characteristics have been found to influence the choice of atypical antipsychotic drugs. However, little is known about the influences on the choice between olanzapine and risperidone in patients with schizophrenia enrolled in Medicaid.

Objective:

The aim of this study was to determine whether demographicand/or clinical characteristics and/or medical-service utilization before treatment were related to the choice of olanzapine versus risperidone therapy using data from a Medicaid population with schizophrenia.

Methods:

The study sample was identified in the North Carolina (NC)Medicaid claims database. Data were included from patients aged 18 to 64 years who were diagnosed with schizophrenia; had initiated treatment with olanzapine or risperidone between July 1, 1998, and October 31, 2000; had not used atypical antipsychotics during the 6 months before the start of treatment; and were continuously eligible in the NC Medicaid program during the 6 months before the start of treatment. Multivariate logistic regression models were used to estimate the likelihood of the choice of olanzapine or risperidone associated with patients' demographic and clinical characteristics and medical-service utilization during the 6 months before the initiation of treatment.

Results:

A total of 764 patients (383 women, 381 men; mean age, 42.1 years)were included in the analysis: 420 were initially prescribed olanzapine and 344 were prescribed risperidone. Men were more likely than women to be prescribed olanzapine compared with risperidone. Patients who had a hospitalization related to a psychiatric condition during the pretreatment period were more likely to be prescribed olanzapine compared with risperidone (OR = 1.530; P = 0.043). Significant regional variation in the likelihood of prescribing olanzapine or risperidone was found, with patients being prescribed risperidone at a higher rate compared with olanzapine in 2 counties with the largest schizophrenic populations.

Conclusions:

In this study of data from patients with schizophrenia identified in the NC Medicaid claims database, sex, a history of psychiatric-related hospitalization, and geographic residence were found to be correlated with the selection of treatment with olanzapine versus risperidone. These findings need to be confirmed in large, randomized, prospective studies.     

Risperidone in Children and Adolescents with Conduct Disorder: A Single-Center, Open-Label Study

Background: Risperidone is one of the most commonly used atypical antipsychotic drugs in the treatment of children and adolescents. However, the data about its use in children and adolescents with conduct disorder (CD) are limited.Objective: The aim of this study was to investigate the effectiveness and tolerability of risperidone in controlling major symptoms of CD in children and adolescents diagnosed with attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and severe CD.Methods: Children and adolescents were eligible for this single-center, open-label study if they met the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnostic criteria for ADHD and ODD and also were diagnosed with severe CD. The patients were treated with risperidone in an open-label fashion for 8 weeks, starting at a daily dosage of 0.25 mg or 0.5 mg (depending on their body weight) in 2 divided doses.Results: The study population comprised 21 children and adolescents (17 boys, 4 girls) with a mean (SD) age of 10.8 (3.6) years. The mean (SD) dosage of risperidone at the end of 8 weeks of treatment was 1.27 (0.42) mg/d (range, 0.75-2.0 mg/d). On the basis of the global improvement subscale of the Clinical Global Impression scale, 16 of 20 patients (80%) were classified as responders. Significant improvements were observed after risperidone treatment in the inattention, hyperactivity/impulsivity, ODD, and CD subscales of the Turgay DSM-IV-Based Child and Adolescent Behavior Disorders Screening and Rating Scale (parent and teacher forms). No severe adverse events were reported.Conclusions: The results of this study are consistent with previous findings and suggest that risperidone may be an effective and well-tolerated atypical antipsychotic drug for the treatment of children and adolescents with CD. However, further studies, particularly placebo-controlled and double-blinded, are needed to better define the clinical use of risperidone in children and adolescents with CD.     

TRPV4 is necessary for trigeminal irritant pain and functions as a cellular formalin receptor

Detection of external irritants by head nociceptor neurons has deep evolutionary roots. Irritant-induced aversive behavior is a popular pain model in laboratory animals. It is used widely in the formalin model, where formaldehyde is injected into the rodent paw, eliciting quantifiable nocifensive behavior that has a direct, tissue-injury-evoked phase, and a subsequent tonic phase caused by neural maladaptation. The formalin model has elucidated many antipain compounds and pain-modulating signaling pathways. We have adopted this model to trigeminally innervated territories in mice. In addition, we examined the involvement of TRPV4 channels in formalin-evoked trigeminal pain behavior because TRPV4 is abundantly expressed in trigeminal ganglion (TG) sensory neurons, and because we have recently defined TRPV4’s role in response to airborne irritants and in a model for temporomandibular joint pain. We found TRPV4 to be important for trigeminal nocifensive behavior evoked by formalin whisker pad injections. This conclusion is supported by studies with Trpv4^−/− mice and TRPV4-specific antagonists. Our results imply TRPV4 in MEK-ERK activation in TG sensory neurons. Furthermore, cellular studies in primary TG neurons and in heterologous TRPV4-expressing cells suggest that TRPV4 can be activated directly by formalin to gate Ca²⁺. Using TRPA1-blocker and Trpa1^−/− mice, we found that both TRP channels co-contribute to the formalin trigeminal pain response. These results imply TRPV4 as an important signaling molecule in irritation-evoked trigeminal pain. TRPV4-antagonistic therapies can therefore be envisioned as novel analgesics, possibly for specific targeting of trigeminal pain disorders, such as migraine, headaches, temporomandibular joint, facial, and dental pain, and irritation of trigeminally innervated surface epithelia.     

Symptom burden in head and neck cancer: impact upon oral energy and protein intake

Purpose

This study explored relationships between oral symptom burden (xerostomia, thick secretions, and mucosal sensitivity), energy and protein intake, and weight change over time among head and neck cancer (HNC) patients who have completed concurrent chemoradiation (CCR).

Methods

Symptom burden was assessed utilizing the Vanderbilt Head and Neck Symptom Survey version 2.0. Weight change was measured from diagnosis to treatment completion, and to the early, mid, and late recovery stage. Energy and protein intake were determined utilizing 24-h diet recalls.

Results

Forty-three adult patients treated for HNC enrolled in the study. Mean percentage weight loss from diagnosis to treatment completion was 7.91?±?4.06 %. Within the mid-recovery stage significant inverse relationships were found between oral protein intake and xerostomia and mucosal sensitivity (r?=??0.818, p?=?0.012; r?=??0.726, p?=?0.032, respectively). After controlling for weight change, significant inverse relationships were found within the mid-recovery stage between oral energy intake and xerostomia and mucosal sensitivity (r?=??0.740, p?=?0.046; r?=??0.751, p?=?0.043, respectively). Significant, inverse relationships were also found between oral protein intake and xerostomia and mucosal sensitivity (r?=??0.835, p?=?0.019; r?=??0.726, p?=?0.033, respectively).

Conclusions

Xerostomia and mucosal sensitivity were significantly related to oral energy and protein intake post-CCR in mid-recovery. Weight loss was greatest from diagnosis to treatment completion and continued through the mid-recovery stage. Assessment of oral symptom burden (xerostomia and mucosal sensitivity) and its impact on oral intake and weight post-CCR should be conducted routinely in good patient care.     

Glucocorticoids exacerbate obesity and insulin resistance in neuron-specific proopiomelanocortin-deficient mice

Null mutations of the proopiomelanocortin gene (Pomc) cause obesity in humans and rodents, but the contributions of central versus pituitary POMC deficiency are not fully established. To elucidate these roles, we introduced a POMC transgene (Tg) that selectively restored peripheral melanocortin and corticosterone secretion in Pomc mice. Rather than improving energy balance, the genetic replacement of pituitary POMC in PomcTg mice aggravated their metabolic syndrome with increased caloric intake and feed efficiency, reduced oxygen consumption, increased subcutaneous, visceral, and hepatic fat, and severe insulin resistance. Pair-feeding of PomcTg mice to the daily intake of lean controls normalized their rate of weight gain but did not abolish obesity, indicating that hyperphagia is a major but not sole determinant of the phenotype. Replacement of corticosterone in the drinking water of Pomc mice recapitulated the hyperphagia, excess weight gain and fat accumulation, and hyperleptinemia characteristic of genetically rescued PomcTg mice. These data demonstrate that CNS POMC peptides play a critical role in energy homeostasis that is not substituted by peripheral POMC. Restoration of pituitary POMC expression to create a de facto neuronal POMC deficiency exacerbated the development of obesity, largely via glucocorticoid modulation of appetite, metabolism, and energy partitioning.     

MECP2 disorders: from the clinic to mice and back

Two severe, progressive neurological disorders characterized by intellectual disability, autism, and developmental regression, Rett syndrome and MECP2 duplication syndrome, result from loss and gain of function, respectively, of the same critical gene, methyl-CpG–binding protein 2 (MECP2). Neurons acutely require the appropriate dose of MECP2 to function properly but do not die in its absence or overexpression. Instead, neuronal dysfunction can be reversed in a Rett syndrome mouse model if MeCP2 function is restored. Thus, MECP2 disorders provide a unique window into the delicate balance of neuronal health, the power of mouse models, and the importance of chromatin regulation in mature neurons. In this Review, we will discuss the clinical profiles of MECP2 disorders, the knowledge acquired from mouse models of the syndromes, and how that knowledge is informing current and future clinical studies.     

Effect of Corncob Bedding on Feed Conversion Efficiency in a High-Fat Diet-Induced Prediabetic Model in C57Bl/6J Mice

Laboratory facilities use many varieties of contact bedding, including wood chips, paper products, and corncob, each with its own advantages and disadvantages. Corncob bedding, for example, is often used because of its high absorbency, ability to minimize detectable ammonia, and low cost. However, observations that mice eat the corncob lead to concerns that its use can interfere with dietary studies. We evaluated the effect of corncob bedding on feed conversion (change in body weight relative to the apparent number of kcal consumed over 7 d) in mice. Four groups of mice (6 to 12 per group) were housed in an individually ventilated caging system: (1) low-fat diet housed on recycled paper bedding, (2) low-fat diet housed on corncob bedding, (3) high-fat diet housed on recycled paper bedding, and (4) high-fat diet housed on corncob bedding. After 4 wk of the high-fat diet, feed conversion and percentage body weight change both were lower in corncob-bedded mice compared with paper-bedded mice. Low-fat–fed mice on corncob bedding versus paper bedding did not show statistically significant differences in feed conversion or change in percentage body weight. Average apparent daily feed consumption did not differ among the 4 groups. In conclusion, these data suggest that corncob bedding reduces the efficiency of feed conversion in mice fed a high-fat diet and that other bedding choices should be favored in these models.Abbreviations: CC, corncob bedding; HF, high-fat diet; LF, low-fat diet; P, paper beddingThe Guide to the Care and Use of Laboratory Animals (the Guide) is used as a reference for the standard of care for many laboratory animals. Under rodent housing, the Guide suggests the use of contact bedding on solid-bottom caging for all rodents for both enrichment of environment and to absorb urine and minimize ammonia buildup.² Many beddings that have been tested for absorbency, comfort, cost, biodegradability, toxicity, and effects on research are available for rodent housing.^9,11 Corncob bedding is a common choice for rodent bedding because of its biodegradability, ability to decrease the amount of detectable ammonia,⁷ high absorbency per unit volume,¹ and cost.An active area of animal research involves modeling the weight gain that is seen in the average human diet in Western societies and that induces insulin resistance and prediabetes. Unintentional effects of housing conditions, including the potential effects of corncob bedding on metabolic parameters, need to be avoided in these models. In addition to uncontrolled dietary intake, corncob bedding has been associated with decreased time spent in slow-wave sleep, presumably because of decreased comfort⁴ in rats. These findings prompt the concern that corncob bedding might also alter activity status, a parameter affects intended weight gain.Here, we conducted a retrospective analysis of weight gain, apparent feed consumption, and feed efficiency of mice housed on corncob bedding compared with recycled paper bedding and fed either low-fat or high-fat diet. This study resulted from a noticeable reduction in expected weight gain in an established high-fat–fed mouse model of obesity and prediabetes after animals were moved from one building within a facility that routinely uses recycled paper bedding to another building that uses corncob bedding. This decrease in weight gain continued for weeks past the expected acclimation to transportation and the new facility. We hypothesized that this suppression in weight gain was associated with the use of corncob bedding.     

Human SH2B1 mutations are associated with maladaptive behaviors and obesity

Src homology 2 B adapter protein 1 (SH2B1) modulates signaling by a variety of ligands that bind to receptor tyrosine kinases or JAK-associated cytokine receptors, including leptin, insulin, growth hormone (GH), and nerve growth factor (NGF). Targeted deletion of Sh2b1 in mice results in increased food intake, obesity, and insulin resistance, with an intermediate phenotype seen in heterozygous null mice on a high-fat diet. We identified SH2B1 loss-of-function mutations in a large cohort of patients with severe early-onset obesity. Mutation carriers exhibited hyperphagia, childhood-onset obesity, disproportionate insulin resistance, and reduced final height as adults. Unexpectedly, mutation carriers exhibited a spectrum of behavioral abnormalities that were not reported in controls, including social isolation and aggression. We conclude that SH2B1 plays a critical role in the control of human food intake and body weight and is implicated in maladaptive human behavior.