Evidence for altered insulin signaling in the brains of Genetic Absence Epilepsy Rats from Strasbourg

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Molecular mechanisms regulating the assembly and secretion of apolipoprotein B in hamster liver and its overproduction in insulin resistant states

grantor: University of TorontoInsulin-resistant states are commonly associated with lipoprotein abnormalities that are risk factors for coronary heart disease. Hepatic overproduction of apolipoprotein B (apoB)-containing lipoproteins is the hallmark of metabolic dyslipidemia in insulin resistance. We used Syrian golden hamsters to study the mechanisms of hepatic overproduction of apoB-containing lipoproteins, as their lipoprotein metabolism closely resembles that of humans. Our studies revealed that hamster hepatocytes efficiently assemble and secrete apoB-containing very low density lipoprotein (VLDL) particles. We induced an insulin resistant state in the hamster by fructose feeding and studied the effects of insulin resistance on apoB biogenesis. Cellular stability of apoB was significantly increased in insulin resistant hepatocytes, possibly linked to marked suppression of ER-60, an apoB-associated ER cysteine protease. Furthermore, hepatic mRNA levels, protein mass, and activity of microsomal triglyceride transfer protein (MTP), a key enzyme in assembly of apoB-containing lipoproteins were dramatically increased. Overall, VLDL-apoB overproduction in fructose-fed hamsters appeared to result from enhanced post-translational stability of nascent apoB and an enhanced expression of MTP, leading to facilitated assembly and secretion of VLDL. We also investigated hepatic insulin signaling in the fructose-fed hamster model to examine the potential contribution of attenuated insulin signaling to the observed VLDL overproduction. Reduced tyrosine phosphorylation of insulin receptor (IR), and its substrates, reduced PI 3-kinase activity, and attenuated serine/threonine phosphorylation of Akt/PKB confirmed induction of hepatic insulin resistance. Elevation of protein mass and activity of protein tyrosine phosphatase (PTP)-1B appeared to be partly responsible for induction of hepatic insulin resistance. Chronic exposure of control hepatocytes to high insulin attenuated IR phosphorylation and increased PTP-1B levels, coinciding with marked suppression of ER-60 and apoB oversecretion. Improvements in phosphorylation status of the IR, in vitro by treatment with sodium orthovanadate, or in vivo by rosiglitazone treatment, attenuated secretion of apoB from fructose-fed hamster hepatocytes. In summary, induction of whole body and hepatic insulin resistance in the hamster by fructose-feeding is accompanied by a marked hepatic overproduction of VLDL-apoB. The VLDL-apoB overproduction may arise from interplay between hepatic insulin resistance and changes in several key components of the VLDL assembly and secretion process including MTP and ER-60.Ph.D

Cellular Prion Protein (PrPc): Putative Interacting Partners and Consequences of the Interaction

Cellular prion protein (PrPc) is a small glycosylphosphatidylinositol (GPI) anchored protein most abundantly found in the outer leaflet of the plasma membrane (PM) in the central nervous system (CNS). PrPc misfolding causes neurodegenerative prion diseases in the CNS. PrPc interacts with a wide range of protein partners because of the intrinsically disordered nature of the protein’s N-terminus. Numerous studies have attempted to decipher the physiological role of the prion protein by searching for proteins which interact with PrPc. Biochemical characteristics and biological functions both appear to be affected by interacting protein partners. The key challenge in identifying a potential interacting partner is to demonstrate that binding to a specific ligand is necessary for cellular physiological function or malfunction. In this review, we have summarized the intracellular and extracellular interacting partners of PrPc and potential consequences of their binding. We also briefly describe prion disease-related mutations at the end of this review

Plasma soluble prion protein, a potential biomarker for sport-related concussions: a pilot study.

Sport-related mild traumatic brain injury (mTBI) or concussion is a significant health concern to athletes with potential long-term consequences. The diagnosis of sport concussion and return to sport decision making is one of the greatest challenges facing health care clinicians working in sports. Blood biomarkers have recently demonstrated their potential in assisting the detection of brain injury particularly, in those cases with no obvious physical injury. We have recently discovered plasma soluble cellular prion protein (PrP(C)) as a potential reliable biomarker for blast induced TBI (bTBI) in a rodent animal model. In order to explore the application of this novel TBI biomarker to sport-related concussion, we conducted a pilot study at the University of Saskatchewan (U of S) by recruiting athlete and non-athlete 18 to 30 year-old students. Using a modified quantitative ELISA method, we first established normal values for the plasma soluble PrP(C) in male and female students. The measured plasma soluble PrP(C) in confirmed concussion cases demonstrated a significant elevation of this analyte in post-concussion samples. Data collected from our pilot study indicates that the plasma soluble PrP(C) is a potential biomarker for sport-related concussion, which may be further developed into a clinical diagnostic tool to assist clinicians in the assessment of sport concussion and return-to-play decision making

Low-Field Magnetic Stimulation Alleviates MPTP-Induced Alterations in Motor Function and Dopaminergic Neurons in Male Mice

Recent studies show that repetitive transcranial magnetic stimulation (rTMS) improves cognitive and motor functions in patients with Parkinson’s Disease (PD). Gamma rhythm low-field magnetic stimulation (LFMS) is a new non-invasive rTMS technique that generates diffused and low-intensity magnetic stimulation to the deep cortical and subcortical areas. To investigate the potential therapeutic effects of LFMS in PD, we subjected an experimental mouse model to LFMS (as an early treatment). We examined the LFMS effect on motor functions as well as neuronal and glial activities in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated male C57BL/6J mice. Mice received MPTP injection (30 mg/kg, i.p., once daily for 5 days) followed by LFMS treatment, 20 min each day for 7 days. LFMS treatment improved motor functions compared with the sham-treated MPTP mice. Further, LFMS significantly improved tyrosine hydroxylase (TH) and decreased glial fibrillary acidic protein (GFAP) levels in substantia nigra pars compacta (SNpc) and non-significantly in striatal (ST) regions. LFMS treatment improved neuronal nuclei (NeuN) levels in SNpc. Our findings suggest that early LFMS treatment improves neuronal survival and, in turn, motor functions in MPTP-treated mice. Further investigation is required to clearly define the molecular mechanisms by which LFMS improves motor and cognitive function in PD patients

Cannabinoid receptors distribution in mouse cortical plasma membrane compartments

Abstract The type 1 and type 2 cannabinoid receptors (CB1 and CB2 receptors) are class A G protein-coupled receptors (GPCRs) that are activated by endogenous lipids called endocannabinoids to modulate neuronal excitability and synaptic transmission in neurons throughout the central nervous system (CNS), and inflammatory processes throughout the body. CB1 receptor is one of the most abundant GPCRs in the CNS and is involved in many physiological and pathophysiological processes, including mood, appetite, and nociception. CB2 receptor is primarily found on immunomodulatory cells of both the CNS and the peripheral immune system. In this study, we isolated lipid raft and non-lipid raft fractions of plasma membrane (PM) from mouse cortical tissue by using cold non-ionic detergent and sucrose gradient centrifugation to study the localization of CB1 receptor and CB2 receptor. Lipid raft and non-lipid raft fractions were confirmed by flotillin-1, caveolin-1 and transferrin receptor as their protein biomarkers. Both CB1 receptor and CB2 receptor were found in non-raft compartments that is inconsistent with previous findings in cultured cell lines. This study demonstrates compartmentalization of both CB1 receptor and CB2 receptor in cortical tissue and warrants further investigation of CB1 receptor and CB2 receptor compartmental distribution in various brain regions and cell types

Study participants’ description.

<p>Study participants’ description.</p

Comparison between Normal and Post-Concussion.

<p><b>A)</b> Two-tailed unpaired student’s t-test shows post-TBI PrP^C concentrations (n = 6; 2.96 ng/mL <b>±</b> 0.37 SEM) are significantly elevated compared with either offseason athlete baseline concentration (n = 76’ 1.59 ng/mL <b>±</b> 0.07 SEM)(<i>p< 0</i>.<i>0001</i>), or both athletes and non-athletes combined (n = 103; 1.70 ng/mL <b>±</b> 0.07 SEM)(<i>p<0</i>.<i>0001</i>). <b>B)</b> Two-tailed paired t-test shows there was no significant difference between three sets of pre- and post-TBI PrP^C values (<i>p = 0</i>.<i>1666</i>).</p

Evidence for altered insulin signalling in the brains of genetic absence epilepsy rats from Strasbourg

Peer Reviewe