Peripheral Neuropathy Presents Similar Symptoms and Pathological Changes in Both High-Fat Diet and Pharmacologically Induced Pre- and Diabetic Mouse Models

The objective of the study was to compare the effects of experimentally induced type 1 or type 2 diabetes (T1D or T2D) on the functional, structural and biochemical properties of mouse peripheral nerves. Eight-week-old C57BL/6 mice were randomly assigned into three groups, including the control (CTRL, chow-fed), STZ (streptozotocin (STZ)-injected), and HFD (high-fat diet (HFD)-fed) group. After 18-weeks of experimental treatment, HFD mice had higher body weights and elevated levels of plasma lipids, while STZ mice developed hyperglycemia. STZ-treated mice, after an extended period of untreated diabetes, developed motor and sensory nerve conduction-velocity deficits. Moreover, relative to control fibers, pre- and diabetic axons were lower in number and irregular in shape. Animals from both treatment groups manifested a pronounced overexpression of nNOS and a reduced expression of SOD1 proteins in the sciatic nerve, indicating oxidative–nitrosative stress and ineffective antioxidant protection in the peripheral nervous system of these mice. Collectively, STZ- and HFD-treated mice revealed similar characteristics of peripheral nerve damage, including a number of morphological and electrophysiological pathologies in the sciatic nerve. While hyperglycemia is a large component of diabetic neuropathy pathogenesis, the non-hyperglycemic effects of diabetes, including dyslipidemia, may also be of importance in the development of this condition

Isolation and identification of endogenous RFamide-related peptides 1 and 3 in the mouse hypothalamus.

Although the RFamide-related peptide (RFRP) preproprotein sequence is known in mice, until now, the molecular structure of the mature, functional peptides processed from the target precursor molecule has not been determined. In the present study, we purified endogenous RFRP1 and RFRP3 peptides from mouse hypothalamic tissue extracts using an immunoaffinity column conjugated with specific antibodies against the mouse C-terminus of RFRP-1 and RFRP-3. Employing liquid chromatography coupled with mass spectrometry, we demonstrated that RFRP1 consists of 15 amino acid residues and RFRP3 consists of 10 amino acid residues (ANKVPHSAANLPLRF-NH2 and SHFPSLPQRF-NH2, respectively). To investigate the distribution of RFRPs in the mouse central nervous system, we performed immunohistochemical staining of the brain sections collected from wild-type and Rfrp knockout animals. These data, together with gene expression in multiple tissues, provide strong confidence that RFRP-immunoreactive neuronal cells are localised in the dorsomedial hypothalamic nucleus (DMH) and between the DMH and the ventromedial hypothalamic nuclei. The identification of RFRP1 and RFRP3 peptides and immunohistochemical visualisation of targeting RFRPs neurones in the mice brain provide the basis for further investigations of the functional biology of RFRPs

Npvf: Hypothalamic Biomarker of Ambient Temperature Independent of Nutritional Status

<div><p>The mechanism by which mice, exposed to the cold, mobilize endogenous or exogenous fuel sources for heat production is unknown. To address this issue we carried out experiments using 3 models of obesity in mice: C57BL/6J+/+ (wild-type B6) mice with variable susceptibility to obesity in response to being fed a high-fat diet (HFD), B6. <i>Ucp1-/-</i> mice with variable diet-induced obesity (DIO) and a deficiency in brown fat thermogenesis and B6. <i>Lep-/-</i> with defects in thermogenesis, fat mobilization and hyperphagia. Mice were exposed to the cold and monitored for changes in food intake and body composition to determine their energy balance phenotype. Upon cold exposure wild-type B6 and <i>Ucp1-/-</i> mice with diet-induced obesity burned endogenous fat in direct proportion to their fat reserves and changes in food intake were inversely related to fat mass, whereas leptin-deficient and lean wild-type B6 mice fed a chow diet depended on increased food intake to fuel thermogenesis. Analysis of gene expression in the hypothalamus to uncover a central regulatory mechanism revealed suppression of the <i>Npvf</i> gene in a manner that depends on the reduced ambient temperature and degree of exposure to the cold, but not on adiposity, leptin levels, food intake or functional brown fat.</p></div

Changes in endogenous substrate utilization and food intake associated with cold-induced thermogenesis in mice with variable levels of DIO.

<p>Diet-induced increase in body weight (A). Reduction in body weight during cold exposure (B). Changes in body weight (C), fat mass (D), and fat free mass (E) before and after 4 days at 4°C. Daily changes in food intake during 4 consecutive days at 4°C (F). Comparison of energy utilization from endogenous reserves and food intake in greater obese and lesser obese B6 mice (G). Correlations between daily increase in food consumed and internal body reserves mobilized per day during 4 days in the cold (H). Data are expressed as mean ± SEM. *, significant differences (<i>t</i> test, *, <i>P</i> < 0.05; **, <i>P</i> < 0.01; ***, <i>P</i> < 0.005; ****, <i>P</i> < 0.001). FI, food intake; FM, fat mass; FFM, fat free mass.</p

Insulin and leptin resistance in wild-type B6 DIO mice.

<p>Changes in plasma free fatty acids (A) and insulin (B) before and after 4 and 7 days at 4°C in greater and lesser obese B6 mice. Correlation between fat mass and plasma leptin levels in DIO mice (C). Changes in plasma leptin (D) before and after 4 and 7 days at 4°C in DIO mice. Changes in food intake and body weight and composition (E) in mice administered with leptin at 24 and 4°C. Data are expressed as mean ± SEM. *, significant differences (<i>t</i> test, *, <i>P</i> < 0.05; **, <i>P</i> < 0.01; ***, <i>P</i> < 0.005).</p

Changes in endogenous substrate utilization and food intake in cold-exposed <i>Ucp1-/-</i> and <i>Ucp1+/</i>? mice with DIO.

<p>Changes in body weight (A), fat mass (B), fat free mass (C), and food intake (D) measured at normal ambient temperature (24°C) and during the cold adaptation protocol. Comparison of energy utilization from endogenous reserves and food intake in <i>Ucp1-/-</i> and <i>Ucp1+/</i>? controls (E). Data are expressed as mean ± SEM. *, significant differences between mice (<i>t</i> test, *, <i>P</i> < 0.05; **, <i>P</i> < 0.01; ***, <i>P</i> < 0.005; ****, <i>P</i> < 0.001). FI, food intake; FM, fat mass; FFM, fat free mass.</p

<i>Npvf</i> gene is a hypothalamic biomarker of cold-activated thermogenesis.

<p>List of the genes that were similarly regulated upon cold exposure in <i>Lep-/-</i> and wild-type <i>Lep+/+</i> mice (A). Verification of microarray data using qRT-PCR in <i>Lep-/-</i> and wild-type <i>Lep+/+</i> mice (B). Data are expressed as mean ± SEM. *, significant differences between mice (<i>t</i> test, *, <i>P</i> < 0.05; **, <i>P</i> < 0.01; ***, <i>P</i> < 0.005; ****, <i>P</i> < 0.001). Fold change (FC) was calculated based on normalized signal values.</p