👤 Ayako Nagayama

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) confer cardio-renal protection, and recent work implicates enhanced branched-chain amino acid (BCAA) catabolism as a potential mechanism in the heart. Whether SGLT2i also promotes renal BCAA catabolism is largely unknown. We hypothesized that SGLT2i enhances renal BCAA catabolism independently of glycemic effects. We conducted a prospective, single-center, open-label, nonrandomized, controlled clinical study in patients with type 2 diabetes stably treated with insulin, who were assigned to dapagliflozin (5 mg/day with dose-reduced insulin; n=8/9 completed) or insulin dose-up (n=5/8 completed). At 12 weeks, changes in urinary and plasma metabolites and short-chain acylcarnitines related to BCAA catabolism were quantified. To explore mechanisms, 10-week-old db/db mice received luseogliflozin (10 mg/kg/day, p.o.) or insulin glargine (10 U/day, s.c.) for 4 weeks; renal histology, mRNA and protein expression of key enzymes involved in BCAA catabolism, including branched-chain aminotransferase 2 (BCAT2), branched-chain ketoacid dehydrogenase (BCKDH), and BCKD kinase (BCKDK), were assessed. Dapagliflozin treatment induced greater increases in urinary excretion of three BCAA-derived metabolites-3-hydroxypropionic acid, C5-OH carnitine, and 3-hydroxybutyric acid-compared with insulin at comparable glycemic levels. In contrast, C4 carnitine (an earlier metabolite in valine catabolism) rose more with insulin. No corresponding between-group differences were detected in plasma metabolites. In db/db mice, luseogliflozin attenuated glomerular mesangial expansion and tubular epithelial atrophy, and reduced Col1a1 mRNA and TGF-β1 protein, compared with glargine at comparable glycemic levels. Luseogliflozin decreased the phosphorylated (inactive) form of the BCKDH E1α subunit (p-BCKDHA/BCKDHA) and lowered BCKDK protein. mRNA expression of amino acid transporters and BCAT2 expression was unchanged. Across complementary human and mouse studies, SGLT2 inhibition was suggested to enhance renal BCAA catabolism compared with insulin at comparable glycemic levels. In humans, increases in urinary BCAA-derived downstream metabolites without corresponding changes in plasma support a kidney-localized metabolic effect. In mice, SGLT2 inhibitor improved renal histopathology, and reduced phosphorylation-mediated inactivation of BCKDH. These findings provide mechanistic, translational evidence that SGLT2i modulate BCAA flux independently of glucose lowering, suggesting BCAA catabolism as a therapeutic axis in diabetic kidney disease. https://rctportal.mhlw.go.jp/en/detail?trial_id=UMIN000052955, identifier UMIN000052955. Show less

The onset and progression mechanisms of metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH) are being studied. We developed and analyzed a new mouse model of obesity by combining maternal Id-like molecule (Maid) and melanocortin-4 receptor (Mc4r) gene deletions. Four mice, each at 12 and 28 weeks of age, were analyzed for each genotype: Maid gene knockout, Mc4r gene knockout, combined Mc4r and Maid gene knockout, and Mc4r gene knockout with a high-fat diet. Mice with a combined deficiency of Mc4r and Maid gene showed significantly more severe obesity compared to all other genotypes, but no liver fibrosis or a decline in metabolic status were observed. In visceral white adipose tissue, Maid and Mc4r gene knockout mice had fewer CD11c-positive cells and lower mRNA expression of both inflammatory and anti-inflammatory cytokines. Furthermore, Maid and Mc4r gene knockout mice showed lower expression of adipocytokines in visceral white adipose tissue and uncoupling protein-1 in scapular brown adipose tissue. The expression of adipocytokines and uncoupling protein-1 is regulated by sympathetic nerve signaling that contribute severe obesity in Maid and Mc4r gene knockout mice. These mechanisms contribute hyperobesity in Maid and Mc4r gene knockout mice. Show less

Sleep apnea is regarded as an important risk factor in the pathogenesis of Alzheimer disease (AD). Chronic intermittent hypoxia treatment (IHT) given during the sleep period of the circadian cycle in experimental animals is a well-established sleep apnea model. Here we report that transient IHT for 4 days on AD model mice causes Aβ overproduction 2 months after IHT presumably via upregulation of synaptic BACE1, side-by-side with tau hyperphosphorylation. These results suggest that even transient IHT may be sufficient to cause long-lasting changes in the molecules measured as AD biomarkers in the brain. Show less

Cardio-ankle vascular index (CAVI) is an arterial stiffness index that correlates inversely with body mass index (BMI) and subcutaneous fat area. Lipoprotein lipase (LPL) that catalyzes the hydrolysis of serum triglycerides is produced mainly in adipocytes. Serum LPL mass reflects LPL expression in adipose tissue, and its changes correlate inversely with changes in CAVI. We hypothesized that LPL derived from subcutaneous adipose tissue (SAT) suppresses the progression of arteriosclerosis and examined the relationship of LPL gene expression in different adipose tissues and serum LPL mass with CAVI in Japanese patients with severe obesity undergoing laparoscopic sleeve gastrectomy (LSG). This study was a single-center retrospective database analysis. Fifty Japanese patients who underwent LSG and had 1-year postoperative follow-up data were enrolled (mean age 47.5 years, baseline BMI 46.6 kg/m2, baseline HbA1c 6.7%). SAT and visceral adipose tissue (VAT) samples were obtained during LSG surgery. LPL gene expression was analyzed by real-time PCR. Serum LPL mass was measured by ELISA using a specific monoclonal antibody against LPL. At baseline, LPL mRNA expression in SAT correlated positively with serum LPL mass, but LPL mRNA expression in VAT did not. LPL mRNA expression in SAT was correlated, and serum LPL mass tended to correlate inversely with the number of metabolic syndrome symptoms, but LPL mRNA expression in VAT did not. LPL mRNA expression in SAT and CAVI tended to correlate inversely in the group with visceral-to-subcutaneous fat ratio of 0.4 or higher, which is considered metabolically severe. Serum LPL mass increased 1 year after LSG. Change in serum LPL mass at 1 year after LSG tended to be an independent factor inversely associated with change in CAVI. Serum LPL mass reflected LPL mRNA expression in SAT in Japanese patients with severe obesity, and LPL mRNA expression in SAT was associated with CAVI in patients with visceral obesity. The change in serum LPL mass after LSG tended to independently contribute inversely to the change in CAVI. This study suggests that LPL derived from SAT may suppress the progression of arteriosclerosis. Show less

Serotonin (5-HT) is one of the key bioamines of nonalcoholic fatty liver disease (NAFLD). Its mechanism of action in autonomic neural signal pathways remains unexplained; hence, we evaluated the involvement of 5-HT and related signaling pathways via autonomic nerves in NAFLD. Diet-induced NAFLD animal models were developed using wild-type and melanocortin 4 receptor (MC4R) knockout (MC4RKO) mice, and the effects of the autonomic neural axis on NAFLD physiology, 5-HT and its receptors (HTRs), and lipid metabolism-related genes were assessed by applying hepatic nerve blockade. Hepatic neural blockade retarded the progression of NAFLD by reducing 5-HT in the small intestine, hepatic HTR2A and hepatic lipogenic gene expression, and treatment with an HTR2A antagonist reproduced these effects. The effects were milder in MC4RKO mice, and brain 5-HT and HTR2C expression did not correlate with peripheral neural blockade. Our study demonstrates that the autonomic liver-gut neural axis is involved in the etiology of diet-induced NAFLD and that 5-HT and HTR2A are key factors, implying that the modulation of the axis and use of HTR2A antagonists are potentially novel therapeutic strategies for NAFLD treatment. This article has an associated First Person interview with the first author of the paper. Show less

Statins have been reported to increase the plasma concentration of arachidonic acid (AA), an omega-6 long chain polyunsaturated fatty acid (LCPUFA) in several clinical studies indicating that statins affect the endogenous synthesis of LCUFAs. In the present study, we investigated the roles of the intrinsic mevalonate cascade and Rho-dependent pathway in LCPUFA synthesis, especially focusing on fatty acid desaturases (Fads) 2, using the human hepatocellular carcinoma cell line HepG2. Cell number and the activity of caspase-3 and 7 (caspase-3/7) was measured using a commercial kit. Gene expression was analyzed by quantitative real-time PCR. Protein expression was detected by Western blot analysis. Atorvastatin decreased cell viability and increased caspase-3/7 activity in a dose-dependent manner. At lower concentrations, atorvastatin stimulated both mRNA and protein expression of Fads2, and increased mRNA expression of FADS1 and ELVOL5. Both mevalonate and geranylgeranyl-pyrophosphate (GGPP), but not cholesterol, fully reversed atorvastatin-induced upregulation of Fads2, and mevalonate-effected reversal was inhibited by treatment with the Rho-associated protein kinase inhibitor Y-27632. These data clearly demonstrated that in human HepG2 cells, statins affect the endogenous synthesis of LCPUFAs by regulation of not only Fads2, but also Fads1 and Elovl5, through the GGPP-dependent Rho kinase pathway. Show less

Numerous clinical studies have reported that statins increase the plasma concentration of arachidonic acid, which is an ω-6 long-chain polyunsaturated fatty acid (LCPUFA), and decrease the concentrations of eicosapentaenoic acid and docosahexaenoic acid, which are ω‑3 LCPUFAs. These findings indicate that statins may affect the endogenous synthesis of LCPUFAs, which is regulated by fatty acid desaturases (FADSs) and elongation of very long‑chain fatty acids proteins (ELOVLs). The present study aimed to investigate the roles of the intrinsic mevalonate cascade and Rho‑dependent pathway in statin‑induced regulation of these desaturases and elongases, as well as cell viability using mouse 3T3‑L1 cells. mRNA expression was analyzed by quantitative polymerase chain reaction. Treatment with atorvastatin decreased cell viability and increased the mRNA expression levels of Fads1, Fads2 and ELOVL fatty acid elongase 5 (Elovl5) in a dose‑dependent manner. Mevalonate and geranylgeranyl pyrophosphate (GGPP), but not cholesterol, fully reversed the atorvastatin‑induced downregulation of cell viability and upregulation of gene expression; however, mevalonate itself did not affect cell viability and gene expression. The Rho‑associated protein kinase inhibitor Y‑27632 inhibited the mevalonate‑ and GGPP‑mediated reversal of atorvastatin‑induced upregulation of Fads1, Fads2 and Elovl5. These findings indicated that statins may affect the endogenous synthesis of LCPUFAs by regulating Fads1, Fads2 and Elovl5 gene expression via the GGPP‑dependent Rho kinase pathway in mouse 3T3-L1 cells. Show less

Multiple exostoses is a hereditary disease characterized by multiple osteocartilagenous tumors, of which the histological structures are similar to those of normal epiphyses. Genetic linkage has identified three different loci for this disease: EXT1 on 8q, EXT2 on 11p, and EXT3 on 19p. The EXT1 and EXT2 genes were recently isolated and mutation analyses have been performed in a number of patients with different ethnic backgrounds. The data indicate that mutations of these genes occurred in broad regions of each gene, and the loss-of-function mutations were predominant, although there were some missense mutations that may create functionally defective protein. Tumor cells were shown to be homozygous for the mutant allele, which is consistent with the concept of these genes as tumor suppressor genes. Recent progress for the functional analyses has disclosed that these genes encode the protein with glycosyltransferase activity and regulate the diffusion of Hedgehog protein, which is the key molecule for the skeletal development. Further analyses of these genes may provide us with the knowledge for the development of epiphyses, and may open the new research field for the regeneration of epiphyses. Show less