Hiroki Yoshida

Atrial fibrillation (AF) is a common cardiac arrhythmia resulting in increased risk of stroke. Despite highly heritable etiology, our understanding of the genetic architecture of AF remains incomplete. Here we performed a genome-wide association study in the Japanese population comprising 9,826 cases among 150,272 individuals and identified East Asian-specific rare variants associated with AF. A cross-ancestry meta-analysis of >1 million individuals, including 77,690 cases, identified 35 new susceptibility loci. Transcriptome-wide association analysis identified IL6R as a putative causal gene, suggesting the involvement of immune responses. Integrative analysis with ChIP-seq data and functional assessment using human induced pluripotent stem cell-derived cardiomyocytes demonstrated ERRg as having a key role in the transcriptional regulation of AF-associated genes. A polygenic risk score derived from the cross-ancestry meta-analysis predicted increased risks of cardiovascular and stroke mortalities and segregated individuals with cardioembolic stroke in undiagnosed AF patients. Our results provide new biological and clinical insights into AF genetics and suggest their potential for clinical applications.

Chorea-acanthocytosis (CHAC) is a hereditary neurodegenerative disorder with autosomal recessive transmission, in which selective degeneration of striatum has been reported in brain pathology. Clinically, CHAC shows Huntington's disease-like neuropsychiatric symptoms and red blood cell acanthocytosis. Recently, we identified the gene, CHAC, encoding a novel protein, chorein, in which a deletion mutation was found in Japanese families with CHAC. In the present study, we have identified the mouse CHAC cDNA sequence and the exon-intron structures of the gene and produced a CHAC model mouse introducing no. 60-61 exon deletion corresponding to a human disease mutation by a gene-targeting technique. The mice began to show acanthocytosis and motor disturbance in old age. In behavioral observations, locomotor activity was significantly decreased and the contact time at social interaction test was decreased significantly in the model mice. In the brain pathology, many apoptotic cells were observed in the striatum of the mutant mice. In neurochemical determinations, the dopamine metabolite, homovanillic acid, concentration decreased significantly in the portion including the midbrain of the mutant mice. These findings are consistent with the human results reported elsewhere and indicate that the CHAC model mice showed a mild phenotype with late adult onset. The CHAC model mouse therefore provides a good model system to study the human disease.

Novel atherosclerotic lesions were induced in the Microminipig (MMP, registered with the Japanese Ministry of Agriculture, Forestry and Fisheries as a novel variety of swine), the smallest pig available for experimental use, by feeding a high fat (12%) and high cholesterol (5%) diet (HFCD) with sodium cholate (SC, 0.7%) (HFCD/SC) for three months. Three MMPs were used: a male fed with normal diet (M-ND), and a male and an ovariectomized female fed with HFCD/SC (M-HFCD/SC and Fx-HFCD/SC). HFCD/SC induced hypercholesterolemia accompanied by an increase in serum total cholesterol (T-Cho), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and cholesterol ester (CE) from the first week. Serum levels of T-Cho, LDL-C and CE reached a maximum in two to three weeks, and HDL-C gradually increased during the experimental period (duration). Serum lipoprotein analysis showed a dominant LDL-C fraction, as seen in humans, in all three MMPs. Body weight gain in the MMPs fed with HFCD/SC was greater than in the animal fed with M-ND. At the end of the experiment, computed tomography scans of conscious animals showed increases in subcutaneous and abdominal fat in those fed with HFCD/SC, suggesting the induction of obesity. Atherosclerotic lesions in systemic arteries (including external and internal iliac arteries, abdominal aorta, coronary artery, cerebral arterial circle), fatty changes, and foamy cell infiltration in the liver and spleen were histopathologically observed in the MMPs fed with HFCD/SC. Atherosclerosis and the pathological findings induced by HFCD/SC in MMPs were similar to the pathological changes associated with human atherosclerosis, suggesting that the MMP has the potential to be a suitable animal model for human atherosclerosis.

Scope Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common chronic liver disease worldwide, defined by hepatic over‐accumulation of lipids without significant ethanol consumption. Pharmacological or bioactive food ingredients that suppress hepatic lipid accumulation through AMP‐activated protein kinase (AMPK) signaling, which plays a critical role in the regulation of lipid metabolism, are searched. Methods and results It is found that tomatidine, the aglycone of α‐tomatine abundant in green tomatoes, significantly inhibits palmitate‐provoked lipid accumulation and stimulates phosphorylation of AMPK and acetyl‐CoA carboxylase 1 (ACC1) in human HepG2 hepatocytes. The results also indicate that tomatidine can enhance triglyceride turnover and decline in lipogenesis by upregulating adipose triglyceride lipase (ATGL) and downregulating fatty acid synthase (FAS) via the AMPK signaling‐dependent regulation of transcription factors, element‐binding protein‐1c (SREBP‐1c) and forkhead box protein O1 (FoxO1). Furthermore, mechanistic studies demonstrate that tomatidine‐stimulated AMPK phosphorylation is due to CaMKKβ activation in response to an increase in intracellular Ca 2+ concentration. Finally, it is discovered that tomatidine functions as an agonist for vitamin D receptor to elicit AMPK‐dependent suppression of lipid accumulation. Conclusion The in vitro study suggests the potential efficacy of tomatidine as a preventive and therapeutic treatment in obesity‐related fatty liver diseases.