Further studies on cortical tangential migration in wild type and Pax-6 mutant mice

In this study we present new data concerning the tangential migration from the medial and lateral ganglionic eminences (MGE and LGE) to the cerebral cortex during development. We have used Calbindin as a useful marker to follow the itinerary of tangential migratory cells during early developmental stages in wild-type and Pax-6 homozygous mutant mice. In the wild-type mice, at early developmental stages, migrating cells advance through the intermediate zone (IZ) and preplate (PP). At more advanced stages, migrating cells were present in the subplate (SP) and cortical plate (CP) to reach the entire developing cerebral cortex. We found that, in the homozygous mutant mice (Pax-6 ^Sey-Neu/Pax-6 ^Sey-Neu), this tangential migration is severely affected at early developmental stages: migrating cells were absent in the IZ, which were only found some days later, suggesting that in the mutant mice, there is a temporal delay in tangential migration. We have also defined some possible mechanisms to explain certain migratory routes from the basal telencephalon to the cerebral cortex. We describe the existence of two factors, which we consider to be essential for the normal migration; the first one is the cell adhesion molecule PSA-NCAM, whose role in other migratory systems is well known. The second factor is Robo-2, whose expression delimits a channel for the passage of migratory cells from the basal telencephalon to the cerebral cortex.     

Mutations in the Paxillin-binding Site of Integrin-linked Kinase (ILK) Destabilize the Pseudokinase Domain and Cause Embryonic Lethality in Mice

Integrin-linked kinase (ILK) localizes to focal adhesions (FAs) where it regulates cell spreading, migration, and growth factor receptor signaling. Previous reports showed that overexpressed ILK in which Val³⁸⁶ and Thr³⁸⁷ were substituted with glycine residues (ILK-VT/GG) could neither interact with paxillin nor localize to FA in cells expressing endogenous wild-type ILK, implying that paxillin binding to ILK is required for its localization to FAs. Here, we show that introducing this mutation into the germ line of mice (ILK-VT/GG) caused vasculogenesis defects, resulting in a general developmental delay and death at around embryonic day 12.5. Fibroblasts isolated from ILK-VT/GG mice contained mutant ILK in FAs, showed normal adhesion to and spreading on extracellular matrix substrates but displayed impaired migration. Biochemical analysis revealed that VT/GG substitutions decreased ILK protein stability leading to decreased ILK levels and reduced binding to paxillin and α-parvin. Because paxillin depletion did not affect ILK localization to FAs, the embryonic lethality and the in vitro migration defects are likely due to the reduced levels of ILK-VT/GG and diminished binding to parvins.     

Helicobacter pylori Colonization Ameliorates Glucose Homeostasis in Mice through a PPAR γ-Dependent Mechanism

Background

There is an inverse secular trend between the incidence of obesity and gastric colonization with Helicobacter pylori, a bacterium that can affect the secretion of gastric hormones that relate to energy homeostasis. H. pylori strains that carry the cag pathogenicity island (PAI) interact more intimately with gastric epithelial cells and trigger more extensive host responses than cag⁻ strains. We hypothesized that gastric colonization with H. pylori strains differing in cag PAI status exert distinct effects on metabolic and inflammatory phenotypes.

Methodology/Principal Findings

To test this hypothesis, we examined metabolic and inflammatory markers in db/db mice and mice with diet-induced obesity experimentally infected with isogenic forms of H. pylori strain 26695: the cag PAI wild-type and its cag PAI mutant strain 99–305. H. pylori colonization decreased fasting blood glucose levels, increased levels of leptin, improved glucose tolerance, and suppressed weight gain. A response found in both wild-type and mutant H. pylori strain-infected mice included decreased white adipose tissue macrophages (ATM) and increased adipose tissue regulatory T cells (Treg) cells. Gene expression analyses demonstrated upregulation of gastric PPAR γ-responsive genes (i.e., CD36 and FABP4) in H. pylori-infected mice. The loss of PPAR γ in immune and epithelial cells in mice impaired the ability of H. pylori to favorably modulate glucose homeostasis and ATM infiltration during high fat feeding.

Conclusions/Significance

Gastric infection with some commensal strains of H. pylori ameliorates glucose homeostasis in mice through a PPAR γ-dependent mechanism and modulates macrophage and Treg cell infiltration into the abdominal white adipose tissue.     

Defective adipose tissue development associated with hepatomegaly in cathepsin E-deficient mice fed a high-fat diet

Cathepsin E is an intracellular aspartic proteinase, which is predominantly distributed in immune-related and epithelial cells. However, the role of the enzyme in adipose tissues remains unknown. In this study, we investigated the characteristics of cathepsin E-deficient (CatE^−/−) mice fed a high-fat diet (HFD), as a mouse model of obesity. HFD-fed CatE^−/− mice displayed reduced body weight gain and defective development of white adipose tissue (WAT) and brown adipose tissue (BAT), compared with HFD-fed wild-type mice. Moreover, fat-induced CatE^−/− mice showed abnormal lipid accumulation in non-adipose tissues characterized by hepatomegaly, which is probably due to defective adipose tissue development. Detailed pathological and biochemical analyses showed that hepatomegaly was accompanied by hepatic steatosis and hypercholesterolemia in HFD-induced CatE^−/− mice. In fat-induced CatE^−/− mice, the number of macrophages infiltrating into WAT was significantly lower than in fat-induced wild-type mice. Thus, the impaired adipose tissue development in HFD-induced CatE^−/− mice was probably due to reduced infiltration of macrophages and may lead to hepatomegaly accompanied by hepatic steatosis and hypercholesterolemia.     

Mutations of the mitochondrial-tRNA modifier MTO1 cause hypertrophic cardiomyopathy and lactic acidosis

Dysfunction of mitochondrial respiration is an increasingly recognized cause of isolated hypertrophic cardiomyopathy. To gain insight into the genetic origin of this condition, we used next-generation exome sequencing to identify mutations in MTO1, which encodes mitochondrial translation optimization 1. Two affected siblings carried a maternal c.1858dup (p.Arg620Lysfs^∗8) frameshift and a paternal c.1282G>A (p.Ala428Thr) missense mutation. A third unrelated individual was homozygous for the latter change. In both humans and yeast, MTO1 increases the accuracy and efficiency of mtDNA translation by catalyzing the 5-carboxymethylaminomethylation of the wobble uridine base in three mitochondrial tRNAs (mt-tRNAs). Accordingly, mutant muscle and fibroblasts showed variably combined reduction in mtDNA-dependent respiratory chain activities. Reduced respiration in mutant cells was corrected by expressing a wild-type MTO1 cDNA. Conversely, defective respiration of a yeast mto1Δ strain failed to be corrected by an Mto1^Pro622∗ variant, equivalent to human MTO1^{Arg620Lysfs∗8}, whereas incomplete correction was achieved by an Mto1^Ala431Thr variant, corresponding to human MTO1^Ala428Thr. The respiratory yeast phenotype was dramatically worsened in stress conditions and in the presence of a paromomycin-resistant (P^R) mitochondrial rRNA mutation. Lastly, in vivo mtDNA translation was impaired in the mutant yeast strains.     

Cataracts and Microphthalmia Caused by a Gja8 Mutation in Extracellular Loop 2

The mouse semi-dominant Nm2249 mutation displays variable cataracts in heterozygous mice and smaller lenses with severe cataracts in homozygous mice. This mutation is caused by a Gja8^R205G point mutation in the second extracellular loop of the Cx50 (or α8 connexin) protein. Immunohistological data reveal that Cx50-R205G mutant proteins and endogenous wild-type Cx46 (or α3 connexin) proteins form diffuse tiny spots rather than typical punctate signals of normal gap junctions in the lens. The level of phosphorylated Cx46 proteins is decreased in Gja8^R205G/R205G mutant lenses. Genetic analysis reveals that the Cx50-R205G mutation needs the presence of wild-type Cx46 to disrupt lens peripheral fibers and epithelial cells. Electrophysiological data in Xenopus oocytes reveal that Cx50-R205G mutant proteins block channel function of gap junctions composed of wild-type Cx50, but only affect the gating of wild-type Cx46 channels. Both genetic and electrophysiological results suggest that Cx50-R205G mutant proteins alone are unable to form functional channels. These findings imply that the Gja8^R205G mutation differentially impairs the functions of Cx50 and Cx46 to cause cataracts, small lenses and microphthalmia. The Gja8^R205G mutation occurs at the same conserved residue as the human GJA8^R198W mutation. This work provides molecular insights to understand the cataract and microphthalmia/microcornea phenotype caused by Gja8 mutations in mice and humans.     

Reduction of hydrogen peroxide stress derived from fatty acid beta-oxidation improves fatty acid utilization in Escherichia coli

Fatty acids are a promising raw material for substance production because of their highly reduced and anhydrous nature, which can provide higher fermentation yields than sugars. However, they are insoluble in water and are poorly utilized by microbes in industrial fermentation production. We used fatty acids as raw materials for l-lysine fermentation by emulsification and improved the limited fatty acid-utilization ability of Escherichia coli. We obtained a fatty acid-utilizing mutant strain by laboratory evolution and demonstrated that it expressed lower levels of an oxidative-stress marker than wild type. The intracellular hydrogen peroxide (H₂O₂) concentration of a fatty acid-utilizing wild-type E. coli strain was higher than that of a glucose-utilizing wild-type E. coli strain. The novel mutation rpsA ^D210Y identified in our fatty acid-utilizing mutant strain enabled us to promote cell growth, fatty-acid utilization, and l-lysine production from fatty acid. Introduction of this rpsA ^D210Y mutation into a wild-type strain resulted in lower H₂O₂ concentrations. The overexpression of superoxide dismutase (sodA) increased intracellular H₂O₂ concentrations and inhibited E. coli fatty-acid utilization, whereas overexpression of an oxidative-stress regulator (oxyS) decreased intracellular H₂O₂ concentrations and promoted E. coli fatty acid utilization and l-lysine production. Addition of the reactive oxygen species (ROS) scavenger thiourea promoted l-lysine production from fatty acids and decreased intracellular H₂O₂ concentrations. Among the ROS generated by fatty-acid β-oxidation, H₂O₂ critically affected E. coli growth and l-lysine production. This indicates that the regression of ROS stress promotes fatty acid utilization, which is beneficial for fatty acids used as raw materials in industrial production.     

A unique allosteric insulin receptor monoclonal antibody that prevents hypoglycemia in the SUR-1−/− mouse model of KATP hyperinsulinism

Loss-of-function mutations of the ß-cell ATP-sensitive potassium channels (K_ATP) cause the most common and severe form of congenital hyperinsulinism (K_ATPHI), a disorder of ß-cell function characterized by severe hypoglycemia. Children with K_ATPHI are typically unresponsive to medical therapy and require pancreatectomy for intractable hypoglycemia. We tested the hypothesis that inhibition of insulin receptor signaling may prevent hypoglycemia in K_ATPHI. To test this hypothesis, we examined the effect of an antibody allosteric inhibitor of the insulin receptor, XMetD, on fasting plasma glucose in a mouse model of K_ATPHI (SUR-1^{? / ?} mice). SUR-1^{? / ?} and wild-type mice received twice weekly intraperitoneal injections of either XMetD or control antibody for 8 wks. Treatment with XMetD significantly decreased insulin sensitivity, and increased hepatic glucose output and fasting plasma glucose. These findings support the potential use of insulin receptor antagonists as a therapeutic approach to control the hypoglycemia in congenital hyperinsulinism.     

Impaired striatal dopamine output of homozygous Wfs1 mutant mice in response to [K<Superscript>+</Superscript>] challenge

Loss of function of the Wfs1 gene causes Wolfram syndrome, a rare multisystem degenerative disorder. Mutant mice with targeted Wfs1 gene disruption (Wfs1 KO) display morphological and behavioral impairments that are not well understood. The present study aimed to investigate the striatal dopamine output of wild-type, heterozygous, and homozygous Wfs1 null-mutant mice using in vivo microdialysis technique. The baseline dopamine output in striatum was similar in all three animal groups. The application of 100 mM [K⁺]-rich modified Ringer solution caused in homozygous Wfs1 mutant mice an increase of dopamine output by 400%, while in wild-type and heterozygous animals, the increase of the dopamine output yielded up to 1,200%. In sum, the homozygous Wfs1 mutant mice (AUC_0–3 = 0.212 nM/μl h) show significantly decreased striatal dopamine output in response to high-concentration [K⁺] challenge as compared with wild-type or heterozygous Wfs1 mutant conspecifics (AUC_0–3 = 0.427 and 0.505 nM/μl h, respectively). This could explain at least some of the behavioral alterations in Wfs1 mutant mice.     

The Polymerase Activity of Mammalian DNA Pol ζ Is Specifically Required for Cell and Embryonic Viability

DNA polymerase ζ (pol ζ) is exceptionally important for maintaining genome stability. Inactivation of the Rev3l gene encoding the polymerase catalytic subunit causes a high frequency of chromosomal breaks, followed by lethality in mouse embryos and in primary cells. Yet it is not known whether the DNA polymerase activity of pol ζ is specifically essential, as the large REV3L protein also serves as a multiprotein scaffold for translesion DNA synthesis via multiple conserved structural domains. We report that Rev3l cDNA rescues the genomic instability and DNA damage sensitivity of Rev3l-null immortalized mouse fibroblast cell lines. A cDNA harboring mutations of conserved catalytic aspartate residues in the polymerase domain of REV3L could not rescue these phenotypes. To investigate the role of REV3L DNA polymerase activity in vivo, a Rev3l knock-in mouse was constructed with this polymerase-inactivating alteration. No homozygous mutant mice were produced, with lethality occurring during embryogenesis. Primary fibroblasts from mutant embryos showed growth defects, elevated DNA double-strand breaks and cisplatin sensitivity similar to Rev3l-null fibroblasts. We tested whether the severe Rev3l^-/- phenotypes could be rescued by deletion of DNA polymerase η, as has been reported with chicken DT40 cells. However, Rev3l^-/- Polh^-/- mice were inviable, and derived primary fibroblasts were as sensitive to DNA damage as Rev3l^-/- Polh^+/+ fibroblasts. Therefore, the functions of REV3L in maintaining cell viability, embryonic viability and genomic stability are directly dependent on its polymerase activity, and cannot be ameliorated by an additional deletion of pol η. These results validate and encourage the approach of targeting the DNA polymerase activity of pol ζ to sensitize tumors to DNA damaging agents.     

A pilot study of direct delivery of hydroxypropyl-beta-cyclodextrin to the lung by the nasal route in a mouse model of Niemann-Pick C1 disease: motor performance is unaltered and lung disease is worsened

We have tested the efficacy of hydroxypropyl-beta-cyclodextrin (HPBCD) delivered by the nasal route in the mouse model of juvenile Niemann-Pick C1 disease (NPC1), as pulmonary disease has not responded to systemic therapy with this drug. Since mice have no gag reflex, coating of the nasal cavity, with possible access to the brain, would be followed by delivery of HPBCD to the lung. While foamy macrophages, containing stored cholesterol, were found in the Npc1 ^nmf164 homozygous mice, a marked inflammatory response was found with inhaled HPBCD, both in mutant and wild-type animals. Slight inflammation also occasionally occurred with saline inhalation. There was no difference between the saline-treated, HPBCD-treated, and untreated Npc1 ^nmf164 homozygous mice for weight, balance beam performance, or coat hanger performance. Interestingly, there was a trend to longer survival in the HPBCD-treated Npc1 ^nmf164 homozygous mice, which, when combined with the survival times of the saline-treated survivals (each of which was not different), became significant.     

Reduction in Tcf7l2 expression decreases diabetic susceptibility in mice

Objective: The WNT signaling pathway effector gene TCF7L2 has been associated with an increased risk of type 2 diabetes. However, it remains unclear how this gene affects diabetic pathogenesis. The goal of this study was to investigate the effects of Tcf7l2 haploinsufficiency on metabolic phenotypes in mice.Experimental Design: Tcf7l2 knockout (Tcf7l^-/-) mice were generated. Because of the early mortality of Tcf7l2^-/- mice, we characterized the metabolic phenotypes of heterozygous Tcf7l2^+/- mice in comparison to the wild-type controls. The mice were fed a normal chow diet or a high fat diet (HFD) for 9 weeks.Results: The Tcf7l2^+/- mice showed significant differences from the wild-type mice with regards to body weight, fasting glucose and insulin levels. Tcf7l2^+/- mice displayed improved glucose tolerance. In the liver of Tcf7l2^+/- mice fed on the HFD, reduced lipogenesis and hepatic triglyceride levels were observed when compared with those of wild-type mice. Furthermore, the Tcf7l2^+/- mice fed on the HFD exhibited decreased peripheral fat deposition. Immunohistochemistry in mouse pancreatic islets showed that endogenous expression of Tcf7l2 was upregulated in the wild-type mice, but not in the Tcf7l2^+/- mice, after feeding with the HFD. However, the haploinsufficiency of Tcf7l2 in mouse pancreatic islets resulted in little changes in glucose-stimulated insulin secretion.Conclusion: These results suggest that decreased expression of Tcf7l2 confers reduction of diabetic susceptibility in mice via regulation on the metabolism of glucose and lipid.     

NIAM-Deficient Mice Are Predisposed to the Development of Proliferative Lesions including B-Cell Lymphomas

Nuclear Interactor of ARF and Mdm2 (NIAM, gene designation Tbrg1) is a largely unstudied inhibitor of cell proliferation that helps maintain chromosomal stability. It is a novel activator of the ARF-Mdm2-Tip60-p53 tumor suppressor pathway as well as other undefined pathways important for genome maintenance. To examine its predicted role as a tumor suppressor, we generated NIAM mutant (NIAM^m/m) mice homozygous for a β-galactosidase expressing gene-trap cassette in the endogenous gene. The mutant mice expressed significantly lower levels of NIAM protein in tissues compared to wild-type animals. Fifty percent of aged NIAM deficient mice (14 to 21 months) developed proliferative lesions, including a uterine hemangioma, pulmonary papillary adenoma, and a Harderian gland adenoma. No age-matched wild-type or NIAM^+/m heterozygous animals developed lesions. In the spleen, NIAM^m/m mice had prominent white pulp expansion which correlated with enhanced increased reactive lymphoid hyperplasia and evidence of systemic inflammation. Notably, 17% of NIAM mutant mice had splenic white pulp features indicating early B-cell lymphoma. This correlated with selective expansion of marginal zone B cells in the spleens of younger, tumor-free NIAM-deficient mice. Unexpectedly, basal p53 expression and activity was largely unaffected by NIAM loss in isolated splenic B cells. In sum, NIAM down-regulation in vivo results in a significant predisposition to developing benign tumors or early stage cancers. These mice represent an outstanding platform for dissecting NIAM''s role in tumorigenesis and various anti-cancer pathways, including p53 signaling.     

The Dual-Specificity Phosphatase 2 (DUSP2) Does Not Regulate Obesity-Associated Inflammation or Insulin Resistance in Mice

Alterations in the immune cell profile and the induction of inflammation within adipose tissue are a hallmark of obesity in mice and humans. Dual-specificity phosphatase 2 (DUSP2) is widely expressed within the immune system and plays a key role promoting immune and inflammatory responses dependent on mitogen-activated protein kinase (MAPK) activity. We hypothesised that the absence of DUSP2 would protect mice against obesity-associated inflammation and insulin resistance. Accordingly, male and female littermate mice that are either wild-type (wt) or homozygous for a germ-line null mutation of the dusp2 gene (dusp2^−/−) were fed either a standard chow diet (SCD) or high fat diet (HFD) for 12 weeks prior to metabolic phenotyping. Compared with mice fed the SCD, all mice consuming the HFD became obese, developed glucose intolerance and insulin resistance, and displayed increased macrophage recruitment and markers of inflammation in epididymal white adipose tissue. The absence of DUSP2, however, had no effect on the development of obesity or adipose tissue inflammation. Whole body insulin sensitivity in male mice was unaffected by an absence of DUSP2 in response to either the SCD or HFD; however, HFD-induced insulin resistance was slightly, but significantly, reduced in female dusp2^−/− mice. In conclusion, DUSP2 plays no role in regulating obesity-associated inflammation and only a minor role in controlling insulin sensitivity following HFD in female, but not male, mice. These data indicate that rather than DUSP2 being a pan regulator of MAPK dependent immune cell mediated inflammation, it appears to differentially regulate inflammatory responses that have a MAPK component.     

A method for studying tissue specificity of maternally affected Drosophila melanogaster mutants: mosaic analysis of cinnamon.

Mosaic analysis is introduced to study tissue specificity of the maternal effect which characterizes the wild-type allele of cinnamon (=cin). The methodology presented is applicable to studies of other maternal effect mutations, as well as to female or male sterility mutations. One hundred and forty-three pal-induced fertile cin-mosaic females were obtained, and the degree to which they were capable of maternally affecting their homozygous cin daughters was correlated to their cuticular and germinal genetic constitution. From this analysis the following conclusions are drawn: (1) The presence of a wild-type (cin⁺) allele in maternal germ cells constitutes a sufficient condition for the full expression of the cin⁺ characteristic maternal effect: All cin offspring derived from such cells have normal viability and eye color. (2) This effect is confined to the descendants of a particular germ cell and does not extend to the descendants of other non-cin⁺ germ cells in the same or in a neighboring ovary. (3) A wild-type allele in a germ cell constitutes a necessary condition for the eye color maternal effect. (4) When a maternal germ line is wholly mutant, nonmutant constitution of an additional focus may result in rescue of more than half of the homozygous cin offspring (all with mutant eye color). Mosaic analysis suggests that this somatic viability focus originates from the posterior region of the blastoderm. These conclusions were tested and confirmed by transplanting heterozygous cin ovaries, wild-type Malphigian tubes, and wild-type fat body into homozygous cin hosts. In addition, transplantations of homozygous cin ovaries into wild-type hosts suggest that the posterior maternal viability focus corresponds to the mesodermal components of the ovaries.     

A Cytochrome cbb3 (Cytochrome c) Terminal Oxidase in Azospirillum brasilense Sp7 Supports Microaerobic Growth

Spectral analysis indicated the presence of a cytochrome cbb₃ oxidase under microaerobic conditions in Azospirillum brasilense Sp7 cells. The corresponding genes (cytNOQP) were isolated by using PCR. These genes are organized in an operon, preceded by a putative anaerobox. The phenotype of an A. brasilense cytN mutant was analyzed. Under aerobic conditions, the specific growth rate during exponential phase (μ_e) of the A. brasilense cytN mutant was comparable to the wild-type specific growth rate (μ_e of approximately 0.2 h⁻¹). In microaerobic NH₄⁺-supplemented conditions, the low respiration of the A. brasilense cytN mutant affected its specific growth rate (μ_e of approximately 0.02 h⁻¹) compared to the wild-type specific growth rate (μ_e of approximately 0.2 h⁻¹). Under nitrogen-fixing conditions, both the growth rates and respiration of the wild type were significantly diminished in comparison to those under NH₄⁺-supplemented conditions. Differences in growth rates and respiration between the wild type and the A. brasilense cytN mutant were less pronounced under these nitrogen-fixing conditions (μ_e of approximately 0.03 h⁻¹ for the wild type and 0.02 h⁻¹ for the A. brasilense cytN mutant). The nitrogen-fixing capacity of the A. brasilense cytN mutant was still approximately 80% of that determined for the wild-type strain. This leads to the conclusion that the A. brasilense cytochrome cbb₃ oxidase is required under microaerobic conditions, when a high respiration rate is needed, but that under nitrogen-fixing conditions the respiration rate does not seem to be a growth-limiting factor.     

Development of a novel pink-eyed dilution mouse model showing progressive darkening of the eyes and coat hair with aging

Oca2^p-cas (oculocutaneous albinism II; pink-eyed dilution castaneus) is a coat color mutant gene on mouse chromosome 7 that arose spontaneously in wild Mus musculus castaneus mice. Mice homozygous for Oca2^p-cas usually exhibit pink eyes and gray coat hair on the non-agouti genetic background, and this ordinary phenotype remains unchanged throughout life. During breeding of a mixed strain carrying this gene on the C57BL/6J background, we discovered a novel spontaneous mutation that causes darkening of the eyes and coat hair with aging. In this study, we developed a novel mouse model showing this unique phenotype. Gross observations revealed that the pink eyes and gray coat hair of the novel mutant young mice became progressively darker in color by approximately 3 months after birth. Light and transmission-electron microscopic observations revealed a marked increase in melanin pigmentation of coat hair shafts and choroid of the eye in the novel mice compared to that in the ordinary mice. Sequence analysis of Oca2^p-cas revealed a 4.1-kb deletion involving exons 15 and 16 of its wild-type gene. However, there was no sequence difference between the two types of mutant mice. Mating experiments suggested that the novel mutant phenotype was not inherited in a simple fashion, due to incomplete penetrance. The novel spontaneous mutant mouse is the first example of progressive hair darkening animals and is an essential animal model for understanding of the regulation mechanisms of melanin biosynthesis with aging.     

Insufficient glucose supply is linked to hypothermia upon cold exposure in high-fat diet-fed mice lacking PEMT

Mice that lack phosphatidylethanolamine N-methyltransferase (Pemt^−/− mice) are protected from high-fat (HF) diet-induced obesity. HF-fed Pemt^−/− mice show higher oxygen consumption and heat production, indicating that more energy might be utilized for thermogenesis and might account for the resistance to diet-induced weight gain. To test this hypothesis, HF-fed Pemt^−/− and Pemt^+/+ mice were challenged with acute cold exposure at 4°C. Unexpectedly, HF-fed Pemt^−/− mice developed hypothermia within 3 h of cold exposure. In contrast, chow-fed Pemt^−/− mice, possessing similar body mass, maintained body temperature. Lack of PEMT did not impair the capacity for thermogenesis in skeletal muscle or brown adipose tissue. Plasma catecholamines were not altered by Pemt genotype, and stimulation of lipolysis was intact in brown and white adipose tissue of Pemt^−/− mice. HF-fed Pemt^−/− mice also developed higher systolic blood pressure, accompanied by reduced cardiac output. Choline supplementation reversed the cold-induced hypothermia in HF-fed Pemt^−/− mice with no effect on blood pressure. Plasma glucose levels were ∼50% lower in HF-fed Pemt^−/− mice compared with Pemt^+/+ mice. Choline supplementation normalized plasma hypoglycemia and the expression of proteins involved in gluconeogenesis. We propose that cold-induced hypothermia in HF-fed Pemt^−/− mice is linked to plasma hypoglycemia due to compromised hepatic glucose production.