Low Sympathetic Tone and Obese Phenotype in Oxytocin‐deficient Mice

Oxytocin (Oxt) is secreted both peripherally and centrally and is involved in several functions including parturition, milk let‐down reflex, social behavior, and food intake. Recently, it has been shown that mice deficient in Oxt receptor develop late‐onset obesity. In this study, we characterized a murin model deficient in Oxt peptide (Oxt^?/?) to evaluate food intake and body weight, glucose tolerance and insulin tolerance, leptin and adrenaline levels. We found that Oxt^?/? mice develop late‐onset obesity and hyperleptinemia without any alterations in food intake in addition to having a decreased insulin sensitivity and glucose intolerance. The lack of Oxt in our murin model also results in lower adrenalin levels which led us to hypothesize that the metabolic changes observed are associated with a decreased sympathetic nervous tone. It has been shown that Oxt neurons in the paraventricular nucleus (PVN) are a component of a leptin‐sensitive signaling circuit between the hypothalamus and caudal brain stem for the regulation of food intake and energy homeostasis. Nevertheless, the lack of Oxt in these mice does not have a direct impact on feeding behavior whose regulation is probably dependent on the complex interplay of several factors. The lack of hyperphagia evident in the Oxt^?/? mice may, in part, be attributed to the developmental compensation of other satiety factors such as cholecystokinin or bombesin‐related peptides which merits further investigation. These findings identify Oxt as an important central regulator of energy homeostasis.     

Impaired thermoregulatory ability of oxytocin-deficient mice during cold-exposure

We analyzed temperature homeostasis in oxytocin-deficient (Oxt(-/-)) mice and found that Oxt(-/-) mice exhibited lower body temperatures than wild-type animals when they were exposed to cold. Oxt(-/-) mice also showed slightly more weight gain, but there were no obvious differences in the morphology of white and brown adipose tissues as between wild-type and Oxt(-/-) mice. In cold-exposed conditions, oxytocin neurons containing c-Fos immunoreactivity existed in the paraventricular nucleus of the hypothalamus. These results suggest that the central oxytocin neurons constitute part of the thermoregulatory system involved in maintaining body temperature in cold environments.     

Increased aggression and lack of maternal behavior in Dio3‐deficient mice are associated with abnormalities in oxytocin and vasopressin systems

Thyroid hormones regulate many aspects of brain development and function, and alterations in the levels of thyroid hormone action lead to abnormal anxiety‐ and depression‐like behaviors. A complement of factors in the brain function independently of circulating levels of hormone to strictly controlled local thyroid hormone signaling. A critical factor is the type 3 deiodinase (DIO3), which is located in neurons and protects the brain from excessive thyroid hormone. Here, we examined whether a local increase in brain thyroid hormone action secondary to DIO3 deficiency is of consequence for social behaviors. Although we did not observe alterations in sociability, Dio3?/? mice of both sexes exhibited a significant increase in aggression‐related behaviors and mild deficits in olfactory function. In addition, 85% of Dio3?/? dams manifested no pup‐retrieval behavior and increased aggression toward the newborns. The abnormal social behaviors of Dio3?/? mice were associated with sexually dimorphic alterations in the physiology of oxytocin (OXT) and arginine vasopressin (AVP), 2 neuropeptides with important roles in determining social interactions. These alterations included low adult serum levels of OXT and AVP, and an abnormal expression of Oxt, Avp and their receptors in the neonatal and adult hypothalamus. Our results demonstrate that DIO3 is essential for normal aggression and maternal behaviors, and indicate that abnormal local regulation of thyroid hormone action in the brain may contribute to the social deficits associated with neurodevelopmental disorders.     

Deletion of the Kv2.1 delayed rectifier potassium channel leads to neuronal and behavioral hyperexcitability

The Kv2.1 delayed rectifier potassium channel exhibits high‐level expression in both principal and inhibitory neurons throughout the central nervous system, including prominent expression in hippocampal neurons. Studies of in vitro preparations suggest that Kv2.1 is a key yet conditional regulator of intrinsic neuronal excitability, mediated by changes in Kv2.1 expression, localization and function via activity‐dependent regulation of Kv2.1 phosphorylation. Here we identify neurological and behavioral deficits in mutant (Kv2.1^?/?) mice lacking this channel. Kv2.1^?/? mice have grossly normal characteristics. No impairment in vision or motor coordination was apparent, although Kv2.1^?/? mice exhibit reduced body weight. The anatomic structure and expression of related Kv channels in the brains of Kv2.1^?/? mice appear unchanged. Delayed rectifier potassium current is diminished in hippocampal neurons cultured from Kv2.1^?/? animals. Field recordings from hippocampal slices of Kv2.1^?/? mice reveal hyperexcitability in response to the convulsant bicuculline, and epileptiform activity in response to stimulation. In Kv2.1^?/? mice, long‐term potentiation at the Schaffer collateral – CA1 synapse is decreased. Kv2.1^?/? mice are strikingly hyperactive, and exhibit defects in spatial learning, failing to improve performance in a Morris Water Maze task. Kv2.1^?/? mice are hypersensitive to the effects of the convulsants flurothyl and pilocarpine, consistent with a role for Kv2.1 as a conditional suppressor of neuronal activity. Although not prone to spontaneous seizures, Kv2.1^?/? mice exhibit accelerated seizure progression. Together, these findings suggest homeostatic suppression of elevated neuronal activity by Kv2.1 plays a central role in regulating neuronal network function .     

The Adipose Tissue Phenotype of Hormone‐Sensitive Lipase Deficiency in Mice

Objective: To directly ascertain the physiological roles in adipocytes of hormone‐sensitive lipase (HSL; E.C. 3.1.1.3), a multifunctional hydrolase that can mediate triacylglycerol cleavage in adipocytes. Research Methods and Procedures: We performed constitutive gene targeting of the mouse HSL gene (Lipe), subsequently studied the adipose tissue phenotype clinically and histologically, and measured lipolysis in isolated adipocytes. Results: Homozygous HSL^?/? mice have no detectable HSL peptide or cholesteryl esterase activity in adipose tissue, and heterozygous mice have intermediate levels with respect to wild‐type and deficient littermates. HSL‐deficient mice have normal body weight but reduced abdominal fat mass compared with normal littermates. Histologically, both white and brown adipose tissues in HSL^?/? mice show marked heterogeneity in cell size, with markedly enlarged adipocytes juxtaposed to cells of normal morphology. In isolated HSL^?/? adipocytes, lipolysis is not significantly increased by β₃‐adrenergic stimulation, but under basal conditions in the absence of added catecholamines, the lipolytic rate of isolated HSL^?/? adipocytes is at least as high as that of cells from normal controls. Cold tolerance during a 48‐hour period at 4 °C was similar in HSL^?/? mice and controls. Overnight fasting was well‐tolerated clinically by HSL^?/? mice, but after fasting, liver triglyceride content was significantly lower in HSL^?/? mice compared with wild‐type controls. Conclusions: In isolated fat cells, the lipolytic rate after β‐adrenergic stimulation is mainly dependent on HSL. However, the observation of a normal rate of lipolysis in unstimulated HSL^?/? adipocytes suggests that HSL‐independent lipolytic pathway(s) exist in fat. Physiologically, HSL deficiency in mice has a modest effect under normal fed conditions and is compatible with normal maintenance of core body temperature during cold stress. However, the lipolytic response to overnight fasting is subnormal.     

Developmental role of the cell adhesion molecule Contactin-6 in the cerebral cortex and hippocampus

The gene encoding the neural cell adhesion molecule Contactin-6 (Cntn6 a.k.a. NB-3) has been implicated as an autism risk gene, suggesting that its mutation is deleterious to brain development. Due to its GPI-anchor at Cntn6 may exert cell adhesion/receptor functions in complex with other membrane proteins, or serve as a ligand. We aimed to uncover novel phenotypes related to Cntn6 functions during development in the cerebral cortex of adult Cntn6^?/? mice. We first determined Cntn6 protein and mRNA expression in the cortex, thalamic nuclei and the hippocampus at P14, which decreased specifically in the cortex at adult stages. Neuroanatomical analysis demonstrated a significant decrease of Cux1+ projection neurons in layers II-IV and an increase of FoxP2+ projection neurons in layer VI in the visual cortex of adult Cntn6^?/? mice compared to wild-type controls. Furthermore, the number of parvalbumin+ (PV) interneurons was decreased in Cntn6^?/? mice, while the amount of NPY+ interneurons remained unchanged. In the hippocampus the delineation and outgrowth of mossy fibers remained largely unchanged, except for the observation of a larger suprapyramidal bundle. The observed abnormalities in the cerebral cortex and hippocampus of Cntn6^?/? mice suggests that Cntn6 serves developmental functions involving cell survival, migration and fasciculation. Furthermore, these data suggest that Cntn6 engages in both trans- and cis-interactions and may be involved in larger protein interaction networks.     

The F box protein S phase kinase-associated protein 2 regulates adipose mass and adipocyte number in vivo

Objective: The etiology of some obesity may involve adipocyte hyperplasia. However, the role of adipocyte number in establishing adipose mass is unclear. Cyclin‐dependent kinase inhibitor p27 regulates activity of cyclin/cyclin‐dependent kinase complexes responsible for cell cycle progression. This protein is critical for establishing adult adipocyte number, and p27 knockout increases adult adipocyte number. The SCF (for Skp1‐Cullin‐F‐box protein) complex targets proteins such as p27 for ubiquitin‐proteosome degradation; the F box protein S phase kinase‐associated protein 2 (Skp2), a component of the SCF complex, specifically recognizes p27 for degradation. We used Skp2 knockout (Skp2^?/?) mice to test whether Skp2 loss decreased adipose mass and adipocyte number. Research Methods and Procedures: We measured body weight, adipose mass, adipocyte diameter and number, and glucose tolerance in wild‐type (WT), Skp2^?/?, and p27^?/?Skp2^?/? mice. Mouse embryo fibroblasts (MEFs) from WT and Skp2^?/? fetuses were differentiated to determine whether Skp2 directly affected adipogenesis. Results: Skp2^?/? mice had a 50% decrease in both subcutaneous and visceral fat pad mass and adipocyte number; these decreases exceeded those in body weight, kidney, or muscle. To test the hypothesis that Skp2 effects on adipocyte number involved p27 accumulation, we used p27^?/?Skp2^?/? double knockout mice. The Skp2^?/? decrements in adipocyte number and fat pad mass were totally reversed in p27^?/?Skp2^?/? mice. Adipogenesis was inhibited in MEFs from Skp2^?/? vs. WT mice, and this inhibition was absent in MEFs from p27^?/?Skp2^?/? mice. Discussion: Our results indicate that Skp2 regulates adipogenesis and ultimate adipocyte number in vivo; thus, Skp2 may contribute to obesity involving adipocyte hyperplasia.     

NOX1 deficiency in apolipoprotein E-knockout mice is associated with elevated plasma lipids and enhanced atherosclerosis

Abstract

Nicotinamide adenine dinucleotide phosphate oxidases (NOX) are enzymes that generate reactive oxygen species (ROS). NOX2 activity in the vascular wall is elevated in hypercholesterolemia, and contributes to oxidative stress and atherogenesis. Here we examined the role of another NOX isoform, NOX1, in atherogenesis in apolipoprotein E-knockout (APOE^?/?) mice fed a Western diet for 14 weeks. Although NOX1 mRNA expression was unchanged in aortas from APOE^?/? versus wild-type mice, expression of the NOX1-specific organizer, NOXO1, was diminished, consistent with an overall reduction in NOX1 activity in APOE^?/? mice. To examine the impact of a further reduction in NOX1 activity, APOE^?/? mice were crossed with NOX1^?/y mice to generate NOX1^?/y/APOE^?/? double-knockouts. NOX1 deficiency in APOE^?/? mice was associated with 30–50% higher plasma very-low-density lipoprotein (VLDL)/LDL and triglyceride levels (P < 0.01). Vascular ROS levels were also elevated by twofold in NOX1^?/y/APOE^?/? versus APOE^?/? mice (P < 0.05), despite no changes in expression of other NOX subunits. Although en face analysis of the descending aorta revealed no differences in plaque area between NOX1^?/y/APOE^?/? and APOE^?/? mice, intimal thickening in the aortic sinus was increased by 40% (P < 0.05) in the double-knockouts. Moreover, NOX1 deficiency was associated with a less stable plaque phenotype; aortic sinus lesions contained 60% less collagen (P < 0.01), 40% less smooth muscle (P < 0.01), and 2.5-fold higher levels of matrix metalloproteinase-9 (P < 0.001) than lesions in APOE^?/? mice. Thus, these data, which suggest a protective role for NOX1 against hyperlipidemia and atherosclerosis in APOE^?/? mice, highlight the complex and contrasting roles of different NOX isoforms (e.g., NOX2 versus NOX1) in vascular pathology.     

DNA repair modulates the vulnerability of the developing brain to alkylating agents

Neurons of the developing brain are especially vulnerable to environmental agents that damage DNA (i.e., genotoxicants), but the mechanism is poorly understood. The focus of the present study is to demonstrate that DNA damage plays a key role in disrupting neurodevelopment. To examine this hypothesis, we compared the cytotoxic and DNA damaging properties of the methylating agents methylazoxymethanol (MAM) and dimethyl sulfate (DMS) and the mono- and bifunctional alkylating agents chloroethylamine (CEA) and nitrogen mustard (HN2), in granule cell neurons derived from the cerebellum of neonatal wild type mice and three transgenic DNA repair strains. Wild type cerebellar neurons were significantly more sensitive to the alkylating agents DMS and HN2 than neuronal cultures treated with MAM or the half-mustard CEA. Parallel studies with neuronal cultures from mice deficient in alkylguanine DNA glycosylase (Aag^?/?) or O⁶-methylguanine methyltransferase (Mgmt^?/?), revealed significant differences in the sensitivity of neurons to all four genotoxicants. Mgmt^?/? neurons were more sensitive to MAM and HN2 than the other genotoxicants and wild type neurons treated with either alkylating agent. In contrast, Aag^?/? neurons were for the most part significantly less sensitive than wild type or Mgmt^?/? neurons to MAM and HN2. Aag^?/? neurons were also significantly less sensitive than wild type neurons treated with either DMS or CEA. Granule cell development and motor function were also more severely disturbed by MAM and HN2 in Mgmt^?/? mice than in comparably treated wild type mice. In contrast, cerebellar development and motor function were well preserved in MAM-treated Aag^?/? or MGMT-overexpressing (Mgmt^Tg+) mice, even as compared with wild type mice suggesting that AAG protein increases MAM toxicity, whereas MGMT protein decreases toxicity. Surprisingly, neuronal development and motor function were severely disturbed in Mgmt^Tg+ mice treated with HN2. Collectively, these in vitro and in vivo studies demonstrate that the type of DNA lesion and the efficiency of DNA repair are two important factors that determine the vulnerability of the developing brain to long-term injury by a genotoxicant.     

HPC‐1/syntaxin 1A and syntaxin 1B play distinct roles in neuronal survival

Two types of syntaxin 1 isoforms, HPC‐1/syntaxin 1A (STX1A) and syntaxin 1B (STX1B), are thought to have similar functions in exocytosis of synaptic vesicles. STX1A^?/? mice which we generated previously develop normally, possibly because of compensation by STX1B. We produced STX1B^?/? mice using targeted gene disruption and investigated their phenotypes. STX1B^?/? mice were born alive, but died before postnatal day 14, unlike STX1A^?/? mice. Morphologically, brain development in STX1B^?/? mice was impaired. In hippocampal neuronal culture, the cell viability of STX1B^?/? neurons was lower than that of WT or STX1A^?/? neurons after 9 days. Interestingly, STX1B^?/? neurons survived on WT or STX1A^?/? glial feeder layers as well as WT neurons. However, STX1B^?/? glial feeder layers were less effective at promoting survival of STX1B^?/? neurons. Conditioned medium from WT or STX1A^?/? glial cells had a similar effect on survival, but that from STX1B^?/? did not promote survival. Furthermore, brain‐derived neurotrophic factor (BDNF) or neurotrophin‐3 supported survival of STX1B^?/? neurons. BDNF localization in STX1B^?/? glial cells was disrupted, and BDNF secretion from STX1B^?/? glial cells was impaired. These results suggest that STX1A and STX1B may play distinct roles in supporting neuronal survival by glia.

     

Lingual deficits in neurotrophin double knockout mice

Brain-derived neurotrophic factor (BDNF) and Neurotrophin 3 (NT-3) are members of the neurotrophin family and are expressed in the developing and adult tongue papillae. BDNF null-mutated mice exhibit specific impairments related to innervation and development of the gustatory system while NT-3 null mice have deficits in their lingual somatosensory innervation. To further evaluate the functional specificity of these neurotrophins in the peripheral gustatory system, we generated double BDNF/NT-3 knockout mice and compared the phenotype to BDNF^?/? and wild-type mice. Taste papillae morphology was severely distorted in BDNF^?/?xNT-3^?/? mice compared to single BDNF^?/? and wild-type mice. The deficits were found throughout the tongue and all gustatory papillae. There was a significant loss of fungiform papillae and the papillae were smaller in size compared to BDNF^?/? and wild-type mice. Circumvallate papillae in the double knockouts were smaller and did not contain any intraepithelial nerve fibers. BDNF^?/?xNT-3^?/? mice exhibited additive losses in both somatosensory and gustatory innervation indicating that BDNF and NT-3 exert specific roles in the innervation of the tongue. However, the additional loss of fungiform papillae and taste buds in BDNF^?/?xNT-3^?/? mice compared to single BDNF knockout mice indicate a synergistic functional role for both BDNF-dependent gustatory and NT-3-dependent somatosensory innervations in taste bud and taste papillae innervation and development.     

Masking Responses to Light in Period Mutant Mice

Masking is an acute effect of an external signal on an overt rhythm and is distinct from the process of entrainment. In the current study, we investigated the phase dependence and molecular mechanisms regulating masking effects of light pulses on spontaneous locomotor activity in mice. The circadian genes, Period1 (Per1) and Per2, are necessary components of the timekeeping machinery and entrainment by light appears to involve the induction of the expression of Per1 and Per2 mRNAs in the suprachiasmatic nuclei (SCN). We assessed the roles of the Per genes in regulating masking by assessing the effects of light pulses on nocturnal locomotor activity in C57BL/6J Per mutant mice. We found that Per1^?/? and Per2^?/? mice had robust negative masking responses to light. In addition, the locomotor activity of Per1^?/?/Per2^?/? mice appeared to be rhythmic in the light-dark (LD) cycle, and the phase of activity onset was advanced (but varied among individual mice) relative to lights off. This rhythm persisted for 1 to 2 days in constant darkness in some Per1^?/?/Per2^?/? mice. Furthermore, Per1^?/?/Per2^?/? mice exhibited robust negative masking responses to light. Negative masking was phase dependent in wild-type mice such that maximal suppression was induced by light pulses at zeitgeber time 14 (ZT14) and gradually weaker suppression occurred during light pulses at ZT16 and ZT18. By measuring the phase shifts induced by the masking protocol (light pulses were administered to mice maintained in the LD cycle), we found that the phase responsiveness of Per mutant mice was altered compared to wild-types. Together, our data suggest that negative masking responses to light are robust in Per mutant mice and that the Per1^?/?/Per2^?/? SCN may be a light-driven, weak/damping oscillator. (Author correspondence: shin.yamazaki@vanderbilt.edu)     

Loss of mitochondrial protease ClpP protects mice from diet‐induced obesity and insulin resistance

Caseinolytic peptidase P (ClpP) is a mammalian quality control protease that is proposed to play an important role in the initiation of the mitochondrial unfolded protein response (UPR^mt), a retrograde signaling response that helps to maintain mitochondrial protein homeostasis. Mitochondrial dysfunction is associated with the development of metabolic disorders, and to understand the effect of a defective UPR^mt on metabolism, ClpP knockout (ClpP^?/?) mice were analyzed. ClpP^?/? mice fed ad libitum have reduced adiposity and paradoxically improved insulin sensitivity. Absence of ClpP increased whole‐body energy expenditure and markers of mitochondrial biogenesis are selectively up‐regulated in the white adipose tissue (WAT) of ClpP^?/? mice. When challenged with a metabolic stress such as high‐fat diet, despite similar caloric intake, ClpP^?/? mice are protected from diet‐induced obesity, glucose intolerance, insulin resistance, and hepatic steatosis. Our results show that absence of ClpP triggers compensatory responses in mice and suggest that ClpP might be dispensable for mammalian UPR^mt initiation. Thus, we made an unexpected finding that deficiency of ClpP in mice is metabolically beneficial.     

Different attentional dysfunctions in eEF2K−/−, IL1RAPL1−/− and SHANK3Δ11−/− mice

A common feature of several psychiatric disorders is the attentional impairment. eEF2K ^?/?, IL1RAPL1 ^?/? and SHANK3Δ11 ^?/? mice were used as animal models consistently linked to changes in synaptic plasticity, learning and memory. All knockout (KO) mice and their corresponding littermates were submitted to the novel object recognition (NOR) and visual object recognition (VOR) tasks. In the NOR, eEF2K^?/? mice exhibited a normal performance in terms of mean discrimination index, while SHANK3Δ11^?/? and IL1RAPL1 ^?/? mice were impaired when a delay of 2 and 24 hours was introduced. Surprisingly, when submitted to VOR, where the two objects were replaced with two shapes delivered from two iPods, all the mutant mice performed worse than those in the NOR. In VOR, the application of motion to different shapes, to increase attention, improved performance in eEF2K ^?/? and IL1RAPL1 ^?/? but not in SHANK3Δ11 ^?/? mice. In SHANK3Δ11 ^?/? mice, attentional deficit was also present even if different motions were applied to the same shapes or when these mice were repeatedly exposed for 5 days to the context. Behavioral analysis showed that eEF2K^?/? and IL1RAPL1 ^?/? mice had a good flexibility tested in the T‐maze. eEF2K^?/? showed normal self‐grooming. On the basis of previous literature data indicating that SHANK3Δ11 ^?/? showed impaired flexibility and reduced sociability, we identified in this genotype the most exhaustive model showing all the core symptoms of autism spectrum disorder including a heavy visual attention deficit. These findings show the importance of VOR to identify mouse models of autism.     

Dual Benefit of Reduced Cx43 on Atherosclerosis in LDL Receptor-Deficient Mice

Paracrine cell-to-cell interactions are crucial events during atherogenesis, however, little is known on the role of gap junctional communication during this process. We recently demonstrated increased expression of Cx43 in intimal smooth muscle cells and in a subset of endothelial cells covering the shoulder of atherosclerotic plaques. The purpose of this study was to examine the role of Cx43 in the development of atherosclerosis in vivo. Atherosclerosis-susceptible LDL receptor-deficient (LDLR^?/?) mice were intercrossed with mice heterozygous for Cx43 (Cx43^+/?mice). Male mice with normal (Cx43^+/+LDLR^?/?) or reduced (Cx43^+/?LDLR^?/?) Cx43 level of 10 weeks old were fed a cholesterol-rich diet (1.25%) for 14 weeks. Both groups of mice showed similar increases in serum lipids and body weight. Interestingly, the progression of atherosclerosis was reduced by 50% (P < 0.01) in the thoraco-abdominal aorta and in the aortic roots of Cx43^+/?LDLR^?/?mice compared with Cx43^+/+LDLR^?/?littermate controls. In addition, atheroma in Cx43^+/?LDLR^?/?mice contained fewer inflammatory cells and exhibited thicker fibrous caps with more collagen and smooth muscle cells, important features associated, in human, with stable atherosclerotic lesions. Thus, reducing Cx43 expression in mice provides beneficial effects on both the progression and composition of the atherosclerotic lesions.     

Aquaporin-4 Mitigates Retrograde Degeneration of Rubrospinal Neurons by Facilitating Edema Clearance and Glial Scar Formation After Spinal Cord Injury in Mice

Atrophy of upper motor neurons hampers axonal regeneration and functional recovery following spinal cord injury (SCI). Apart from the severity of primary injury, a series of secondary pathological damages including spinal cord edema and glial scar formation affect the fate of injured upper motor neurons. The aquaporin-4 (AQP4) water channel plays a critical role in water homeostasis and migration of astrocytes in the central nervous system, probably offering a new therapeutic target for protecting against upper motor neuron degeneration after SCI. To test this hypothesis, we examined the effect of AQP4 deficiency on atrophy of rubrospinal neurons after unilateral rubrospinal tract transection at the fourth cervical level in mice. AQP4 gene knockout (AQP4^?/?) mice exhibited high extent of spinal cord edema at 72 h after lesion compared with wild-type littermates. AQP4^?/? mice showed impairments in astrocyte migration toward the transected site with a greater lesion volume at 1 week after surgery and glial scar formation with a larger cyst volume at 6 weeks. More severe atrophy and loss of axotomized rubrospinal neurons as well as axonal degeneration in the rubrospinal tract rostral to the lesion were observed in AQP4^?/? mice at 6 weeks after SCI. AQP4 expression was downregulated at the lesioned spinal segment at 3 days and 1 week after injury, but upregulated at 6 weeks. These results demonstrated that AQP4 not only mitigates spinal cord damage but also ameliorates retrograde degeneration of rubrospinal neurons by promoting edema clearance and glial scar formation after laceration SCI. This finding supports the notion that AQP4 may be a promising therapeutic target for SCI.     

Sexually dimorphic metabolic responses mediated by CRF<Subscript>2</Subscript> receptor during nutritional stress in mice

Background

Chronic stress is a major contributor in the development of metabolic syndrome and associated diseases, such as diabetes. High-fat diet (HFD) and sex are known modifiers of metabolic parameters. Peptide hormones corticotropin-releasing factor (CRF) and urocortins (UCN) mediate stress responses via activation and feedback to the hypothalamic-pituitary-adrenal (HPA) axis. UCN3 is a marker of pancreatic β-cell differentiation, and UCN2 is known to ameliorate glucose levels in mice rendered diabetic with HFD. CRF receptor 2 (CRF₂) is the only known cognate receptor for UCN2/3. Here, we ascertained the role of CRF₂ in glucose clearance, insulin sensitivity, and other parameters associated with metabolic syndrome in a mouse model of nutritional stress.

Methods

Wild-type (WT) and Crhr2^?/? (null) mice of both sexes were fed either normal chow diet or HFD. After 8 weeks, blood glucose levels in response to glucose and insulin challenge were determined. Change in body and fat mass, plasma insulin, and lipid profile were assessed. Histological evaluation of liver sections was performed.

Results

Here, we show that genotype (Crhr2), sex, and diet were all independent variables in the regulation of blood glucose levels, body and fat mass gain/redistribution, and insulin resistance. Surprisingly, CRF₂-deficient mice (Crhr2^?/?) male mice showed similarly impaired glucose clearance on HFD and chow. HFD-fed female Crhr2^?/? mice redistributed their fat depots that were distinct from wild-type females and male mice on either diet. Blood cholesterol and low-density lipoprotein (LDL) levels were elevated significantly in male Crhr2^?/? mice; female Crhr2^?/? mice were protected. Male, but not female Crhr2^?/? mice developed peripheral insulin resistance. HFD, but not chow-fed wild-type male mice developed hepatic macrovesicular steatosis. In contrast, livers of Crhr2^?/? male mice showed microvesicular steatosis on either diet, whereas livers of female mice on this 8-week HFD regimen did not develop steatosis.

Conclusions

CRF₂ receptor dysregulation is a sexually dimorphic risk factor in development of pre-diabetic and metabolic symptoms.

     

The proximal intestinal Fatty Acid-Binding Proteins liver FABP (LFABP) and intestinal FABP (IFABP) differentially modulate whole body energy homeostasis but are not centrally involved in net dietary lipid absorption: Studies of the LFABP/IFABP double knockout mouse

Proximal intestinal enterocytes expresses both intestinal-fatty acid binding protein (IFABP; FABP2) and liver-FABP (LFABP; FABP1). These FABPs are thought to be important in the net uptake of dietary lipid from the intestinal lumen, however their specific and potentially unique functions in the enterocyte remain incompletely understood. We previously showed markedly divergent phenotypes in LFABP^?/? vs. IFABP^?/? mice fed high-fat diets, with the former becoming obese and the latter remaining lean relative to wild-type (WT) mice, supporting different functional roles for each protein. Interestingly, neither mouse model displayed increased fecal lipid concentration, raising the question of whether the presence of one FABP was sufficient to compensate for absence of the other. Here, we generated an LFABP and IFABP double knockout mouse (DKO) to determine whether simultaneous ablation would lead to fat malabsorption, and to further interrogate the individual vs. overlapping functions of these proteins. Male WT, IFABP^?/?, LFABP^?/?, and DKO mice were fed a low-fat (10 % kcal) or high-fat (45 % kcal) diet for 12 weeks. The body weights and fat mass of the DKO mice integrated those of the LFABP^?/? and IFABP^?/? single knockouts, supporting the notion that IFABP and LFABP have distinct functions in intestinal lipid assimilation that result in downstream alterations in systemic energy metabolism. Remarkably, no differences in fecal fat concentrations were found in the DKO compared to WT, revealing that the FABPs are not required for net intestinal uptake of dietary lipid.     

Heteromeric channels formed by TRPC1, TRPC4 and TRPC5 define hippocampal synaptic transmission and working memory

Canonical transient receptor potential (TRPC) channels influence various neuronal functions. Using quantitative high‐resolution mass spectrometry, we demonstrate that TRPC1, TRPC4, and TRPC5 assemble into heteromultimers with each other, but not with other TRP family members in the mouse brain and hippocampus. In hippocampal neurons from Trpc1/Trpc4/Trpc5‐triple‐knockout (Trpc1/4/5^?/?) mice, lacking any TRPC1‐, TRPC4‐, or TRPC5‐containing channels, action potential‐triggered excitatory postsynaptic currents (EPSCs) were significantly reduced, whereas frequency, amplitude, and kinetics of quantal miniature EPSC signaling remained unchanged. Likewise, evoked postsynaptic responses in hippocampal slice recordings and transient potentiation after tetanic stimulation were decreased. In vivo, Trpc1/4/5^?/? mice displayed impaired cross‐frequency coupling in hippocampal networks and deficits in spatial working memory, while spatial reference memory was unaltered. Trpc1/4/5^?/? animals also exhibited deficiencies in adapting to a new challenge in a relearning task. Our results indicate the contribution of heteromultimeric channels from TRPC1, TRPC4, and TRPC5 subunits to the regulation of mechanisms underlying spatial working memory and flexible relearning by facilitating proper synaptic transmission in hippocampal neurons.