LRRK2 Inhibition Ameliorates Dexamethasone-Induced Glucose Intolerance via Prevents Impairment in GLUT4 Membrane Translocation in Adipocytes

Targeting Glucose Metabolism: A Novel Therapeutic Approach for Parkinson's Disease

Glucose metabolism is essential for the maintenance and function of the central nervous system. Although the brain constitutes only 2% of the body weight, it consumes approximately 20% of the body's total energy, predominantly derived from glucose. This high energy demand of the brain underscores its reliance on glucose to fuel various functions, including neuronal activity, synaptic transmission, and the maintenance of ion gradients necessary for nerve impulse transmission. Increasing evidence shows that many neurodegenerative diseases, including Parkinson's disease (PD), are associated with abnormalities in glucose metabolism. PD is characterized by the progressive loss of dopaminergic neurons in the substantia nigra, accompanied by the accumulation of α-synuclein protein aggregates. These pathological features are exacerbated by mitochondrial dysfunction, oxidative stress, and neuroinflammation, all of which are influenced by glucose metabolism disruptions. Emerging evidence suggests that targeting glucose metabolism could offer therapeutic benefits for PD. Several antidiabetic drugs have shown promise in animal models and clinical trials for mitigating the symptoms and progression of PD. This review explores the current understanding of the association between PD and glucose metabolism, emphasizing the potential of antidiabetic medications as a novel therapeutic approach. By improving glucose uptake and utilization, enhancing mitochondrial function, and reducing neuroinflammation, these drugs could address key pathophysiological mechanisms in PD, offering hope for more effective management of this debilitating disease.

SARS-CoV-2 propagation to the TPH2-positive neurons in the ventral tegmental area induces cell death via GSK3β-dependent accumulation of phosphorylated tau

COVID-19, an infectious disease caused by SARS-CoV-2, was declared a pandemic by the WHO in 2020. Psychiatric symptoms including sleep disturbance, memory impairment, and depression are associated with SARS-CoV-2 infection. These symptoms are causes long-term mental and physical distress in recovering patients; however, the underlying mechanism is unclear. In this study, we determined the effects of SARS-CoV-2 infection on brain tissue using k18hACE2 mice. Using brain tissue from 18hACE2 mice infected with SARS-CoV-2 through intranasal administration, SARS-CoV-2 spike protein and RNA were analyzed by immunohistochemical staining and in-situ hybridization. Immunohistochemical analysis revealed that Tryptophan hydroxylase 2 (TPH2)-positive cells and SARS-CoV-2 spike protein were co-localized in the ventral tegmental area of SARS-CoV-2-infected mice. We observed decreased TPH2 expression and increased accumulation of phosphorylated tau protein and Phospho-Histone H2A.X (γH2AX) expression in the ventral tegmental region. In addition, activation of glycogen synthase kinase 3β (GSK3β) was induced by SARS-CoV-2 infection. Overall, our results suggest that SARS-CoV-2 infection of TPH2-positive cells in the ventral tegmental area induces neuronal cell death through increased accumulation of phosphorylated tau. Attenuation of the GSK3β pathway and decreased serotonin synthesis through suppression of TPH2 expression may contribute to the development of neurological symptoms.

Exercise training and cold exposure trigger distinct molecular adaptations to inguinal white adipose tissue

Exercise training and cold exposure both improve systemic metabolism, but the mechanisms are not well established. Here, we tested the hypothesis that inguinal white adipose tissue (iWAT) adaptations are critical for these beneficial effects and determined the impact of exercise-trained and cold-exposed iWAT on systemic glucose metabolism and the iWAT proteome and secretome. Transplanting trained iWAT into sedentary mice improves glucose tolerance, while cold-exposed iWAT transplantation shows no such benefit. Compared to training, cold leads to more pronounced alterations in the iWAT proteome and secretome, downregulating >2,000 proteins but also boosting the thermogenic capacity of iWAT. In contrast, only training increases extracellular space and vesicle transport proteins, and only training upregulates proteins that correlate with favorable fasting glucose, suggesting fundamental changes in trained iWAT that mediate tissue-to-tissue communication. This study defines the unique exercise training- and cold exposure-induced iWAT proteomes, revealing distinct mechanisms for the beneficial effects of these interventions on metabolic health.

LRRK2 negatively regulates glucose tolerance via regulation of membrane translocation of GLUT4 in adipocytes

Epidemiological studies have shown that abnormalities of glucose metabolism are involved in leucine-rich repeat kinase 2 (LRRK2)-associated Parkinson's disease (PD). However, the physiological significance of this association is unclear. In the present study, we investigated the effect of LRRK2 on high-fat diet (HFD)-induced glucose intolerance using Lrrk2-knockout (KO) mice. We found for the first time that HFD-fed KO mice display improved glucose tolerance compared with their wild-type (WT) counterparts. In addition, high serum insulin and leptin, as well as low serum adiponectin resulting from HFD in WT mice were improved in KO mice. Using western blotting, we found that Lrrk2 is highly expressed in adipose tissues compared with other insulin-related tissues that are thought to be important in glucose tolerance, including skeletal muscle, liver, and pancreas. Lrrk2 expression and phosphorylation of its kinase substrates Rab8a and Rab10 were significantly elevated after HFD treatment in WT mice. In cell culture experiments, treatment with a LRRK2 kinase inhibitor stimulated insulin-dependent membrane translocation of glucose transporter 4 (Glut4) and glucose uptake in mouse 3T3-L1 adipocytes. We conclude that increased LRRK2 kinase activity in adipose tissue exacerbates glucose tolerance by suppressing Rab8- and Rab10-mediated GLUT4 membrane translocation.

Exercise Training and Cold Exposure Trigger Distinct Molecular Adaptations to Inguinal White Adipose Tissue

Exercise training and cold exposure both improve systemic metabolism, but the mechanisms are not well-established. We tested the hypothesis that adaptations to inguinal white adipose tissue (iWAT) are critical for these beneficial effects by determining the impact of exercise-trained and cold-exposed iWAT on systemic glucose metabolism and the iWAT proteome and secretome. Transplanting trained iWAT into sedentary mice improved glucose tolerance, while cold-exposed iWAT transplantation showed no such benefit. Compared to training, cold led to more pronounced alterations in the iWAT proteome and secretome, downregulating >2,000 proteins but also boosting iWAT's thermogenic capacity. In contrast, only training increased extracellular space and vesicle transport proteins, and only training upregulated proteins that correlate with favorable fasting glucose, suggesting fundamental changes in trained iWAT that mediate tissue-to-tissue communication. This study defines the unique exercise training- and cold exposure-induced iWAT proteomes, revealing distinct mechanisms for the beneficial effects of these interventions on metabolic health.

Undaria pinnatifida (Wakame) Intake Ameliorates High-Fat Diet-Induced Glucose Intolerance via Promoting GLUT4 Expression and Membrane Translocation in Muscle

Type 2 diabetes mellitus (T2DM), a lifestyle-related disease, is developed due to eating habits and decreased physical activity. Diabetes also increases the risk of cancer and major neurodegenerative diseases; controlling the onset of diabetes helps prevent various illnesses. Eating seaweed, such as Undaria pinnatifida (wakame), is a part of the Asian food culture. Therefore, we analyzed the antidiabetic effect of wakame intake using the high-fat diet-induced diabetes mouse model. Furthermore, we analyzed the effect of wakame extract on the cell membrane translocation of glucose transporter-4 (GLUT4) and activation of insulin signal molecules, such as AKT and AMPK, in insulin-sensitive tissues. Differentiated C2C12 cells were incubated with wakame components. The membrane translocation of GLUT4 and phosphorylation of AKT and AMPK were investigated with immunofluorescence staining and Western blotting, respectively. Also, male C57BL/6J mice were fed the normal diet (ND), high-fat diet (HFD), ND with 1% wakame powder (ND + W), or HFD with 1% wakame powder (HFD + W). We evaluated the effect of wakame intake on high-fat diet-induced glucose intolerance using an oral glucose tolerance test. Moreover, we analyzed insulin signaling molecules, such as GLUT4, AKT, and AMPK, in muscle using Western blotting. GLUT4 membrane translocation was promoted by wakame components. Also, GLUT4 levels and AKT and AMPK phosphorylation were significantly elevated by wakame components in C2C12 cells. In addition, the area under the curve (AUC) of the HFD + W group was significantly smaller than that of the HFD group. Furthermore, the level of GLUT4 in the muscle was increased in the wakame intake group. This study revealed that various wakame components exerted antidiabetic effects on the mice on a high-fat diet by promoting glucose uptake in the skeletal muscle, enhancing GLUT4 levels, and activating AKT and AMPK.