g(m1)-ganglioside and Diabetes-Mellitus--Type-2

Growing evidence suggests that diabetes mellitus (DM) is one of the strongest risk factors for developing Alzheimer's disease (AD). However, it remains unclear why DM accelerates AD pathology. In cynomolgus monkeys older than 25 years, senile plaques (SPs) are spontaneously and consistently observed in their brains, and neurofibrillary tangles are present at 32 years of age and older. In laboratory-housed monkeys, obesity is occasionally observed and frequently leads to development of type 2 DM. In the present study, we performed histopathological and biochemical analyses of brain tissue in cynomolgus monkeys with type 2 DM to clarify the relationship between DM and AD pathology. Here, we provide the evidence that DM accelerates Aβ pathology in vivo in nonhuman primates who had not undergone any genetic manipulation. In DM-affected monkey brains, SPs were observed in frontal and temporal lobe cortices, even in monkeys younger than 20 years. Biochemical analyses of brain revealed that the amount of GM1-ganglioside-bound Aβ (GAβ)--the endogenous seed for Aβ fibril formation in the brain--was clearly elevated in DM-affected monkeys. Furthermore, the level of Rab GTPases was also significantly increased in the brains of adult monkeys with DM, almost to the same levels as in aged monkeys. Intraneuronal accumulation of enlarged endosomes was also observed in DM-affected monkeys, suggesting that exacerbated endocytic disturbance may underlie the acceleration of Aβ pathology due to DM.

Topics: Age Factors; Alzheimer Disease; Amyloid beta-Peptides; Amyloidosis; Animals; Brain; Cathepsin D; Cerebral Amyloid Angiopathy; Diabetes Mellitus; Diabetes Mellitus, Type 2; Disease Models, Animal; Endocytosis; Female; G(M1) Ganglioside; Immunohistochemistry; Macaca fascicularis; Phagosomes; Plaque, Amyloid; rab GTP-Binding Proteins

The incretin hormone Glucagon-like peptide 1 (GLP-1) requires delivery by injection for the treatment of Type 2 diabetes mellitus. Here, we test if the properties of glycosphingolipid trafficking in epithelial cells can be applied to convert GLP-1 into a molecule suitable for mucosal absorption. GLP-1 was coupled to the extracellular oligosaccharide domain of GM1 species containing ceramides with different fatty acids and with minimal loss of incretin bioactivity. When applied to apical surfaces of polarized epithelial cells in monolayer culture, only GLP-1 coupled to GM1-ceramides with short- or cis-unsaturated fatty acids trafficked efficiently across the cell to the basolateral membrane by transcytosis. In vivo studies showed mucosal absorption after nasal administration. The results substantiate our recently reported dependence on ceramide structure for trafficking the GM1 across polarized epithelial cells and support the idea that specific glycosphingolipids can be harnessed as molecular vehicles for mucosal delivery of therapeutic peptides.

Topics: Amino Acid Sequence; Animals; Cell Line; Ceramides; Diabetes Mellitus, Type 2; Drug Carriers; G(M1) Ganglioside; Glucagon-Like Peptide 1; HEK293 Cells; Humans; Incretins; Male; Mice; Mice, Inbred C57BL; Models, Molecular; Molecular Sequence Data; Transcytosis

To determine whether cholera toxin B subunit and active peptide from shark liver (CTB-APSL) fusion protein plays a role in treatment of type 2 diabetic mice, the CTB-APSL gene was cloned and expressed in silkworm (Bombyx mori) baculovirus expression vector system (BEVS), then the fusion protein was orally administrated at a dose of 100 mg/kg for five weeks in diabetic mice. The results demonstrated that the oral administration of CTB-APSL fusion protein can effectively reduce the levels of both fasting blood glucose (FBG) and glycosylated hemoglobin (GHb), promote insulin secretion and improve insulin resistance, significantly improve lipid metabolism, reduce triglycerides (TG), total cholesterol (TC) and low density lipoprotein (LDL) levels and increase high density lipoprotein (HDL) levels, as well as effectively improve the inflammatory response of type 2 diabetic mice through the reduction of the levels of inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Histopathology shows that the fusion protein can significantly repair damaged pancreatic tissue in type 2 diabetic mice, significantly improve hepatic steatosis and hepatic cell cloudy swelling, reduce the content of lipid droplets in type 2 diabetic mice, effectively inhibit renal interstitial inflammatory cells invasion and improve renal tubular epithelial cell nucleus pyknosis, thus providing an experimental basis for the development of a new type of oral therapy for type 2 diabetes.

Topics: Animals; Baculoviridae; Blood Glucose; Body Weight; Bombyx; Cholera Toxin; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; DNA, Viral; Escherichia coli; G(M1) Ganglioside; Genetic Vectors; Glycated Hemoglobin; Hypoglycemic Agents; Hypolipidemic Agents; Insulin; Insulin Resistance; Kidney; Lipids; Male; Mice; Mice, Inbred ICR; Sharks; Spleen; Viral Fusion Proteins

Type 2 diabetes mellitus is thought to be a significant risk factor for Alzheimer's disease. Insulin resistance also affects the central nervous system by regulating key processes, such as neuronal survival and longevity, learning and memory. However, the mechanisms underlying these effects remain uncertain. To investigate whether insulin resistance is associated with the assembly of amyloid β-protein (Aβ) at the cell surface of neurons, we inhibited insulin-signalling pathways of primary neurons. The treatments of insulin receptor (IR)-knockdown and a phosphatidylinositol 3-kinase inhibitor (LY294002), but not an extracellular signal-regulated kinase inhibitor, induced an increase in GM1 ganglioside (GM1) levels in detergent-resistant membrane microdomains of the neurons. The aged db/db mouse brain exhibited reduction in IR expression and phosphorylation of Akt, which later induced an increase in the high-density GM1-clusters on synaptosomes. Neurons treated with IR knockdown or LY294002, and synaptosomes of the aged db/db mouse brains markedly accelerated an assembly of Aβs. These results suggest that ageing and peripheral insulin resistance induce brain insulin resistance, which accelerates the assembly of Aβs by increasing and clustering of GM1 in detergent-resistant membrane microdomains of neuronal membranes.

Topics: Aging; Amyloid beta-Peptides; Animals; Blotting, Western; Brain Chemistry; Cell Separation; Cells, Cultured; Cholesterol; Chromones; Diabetes Mellitus, Type 2; Enzyme Inhibitors; Fluorescent Dyes; G(M1) Ganglioside; Insulin Resistance; Mice; Morpholines; Neurofibrils; Neurons; Rats; Rats, Sprague-Dawley; Receptor, Insulin; Receptors, Presynaptic; RNA, Small Interfering; Sphingomyelins; Synaptosomes

Topics: Autoantigens; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Diabetic Neuropathies; Female; G(M1) Ganglioside; Humans; Male; Middle Aged; Motor Neuron Disease