GR-KLF15 pathway controls hepatic lipogenesis during fasting

During periods of fasting, the body undergoes a metabolic shift from carbohydrate utilization to the use of fats and ketones as an energy source, as well as the inhibition of de novo lipogenesis and the initiation of gluconeogenesis in the liver. The transcription factor sterol regulatory element-binding protein-1 (SREBP-1), which plays a critical role in the regulation of lipogenesis, is suppressed during fasting, resulting in the suppression of hepatic lipogenesis. We previously demonstrated that the interaction of fasting-induced Kruppel-like factor 15 (KLF15) with liver X receptor serves as the essential mechanism for the nutritional regulation of SREBP-1 expression. However, the underlying mechanisms of KLF15 induction during fasting remain unclear. In this study, we show that the glucocorticoid receptor (GR) regulates the hepatic expression of KLF15 and, subsequently, lipogenesis through the KLF15-SREBP-1 pathway during fasting. KLF15 is necessary for the suppression of SREBP-1 by GR, as demonstrated through experiments using KLF15 knockout mice. Additionally, we show that GR is involved in the fasting response, with heightened binding to the KLF15 enhancer. It has been widely known that the hypothalamic-pituitary-adrenal (HPA) axis regulates the secretion of glucocorticoids and plays a significant role in the metabolic response to undernutrition. These findings demonstrate the importance of the HPA-axis-regulated GR-KLF15 pathway in the regulation of lipid metabolism in the liver during fasting.

Deterioration in right ventricular structure and function over time in patients with heart failure and preserved ejection fraction

AIMS

Prevalent right ventricular (RV) dysfunction (RVD) is associated with increased mortality in patients with heart failure with preserved ejection fraction (HFpEF), but no study has characterized long-term changes in RV structure and function within the same patient.

METHODS AND RESULTS

Patients with unequivocal HFpEF defined by either invasive haemodynamics or hospitalization for pulmonary oedema (n = 271) underwent serial echocardiographic evaluations >6 months apart. Clinical, structural, functional, and haemodynamic characteristics were examined. Over a median of 4.0 years (interquartile range 2.1-6.1), there was a 10% decline in RV fractional area change and 21% increase in RV diastolic area (both P < 0.0001). These changes greatly exceeded corresponding changes in the left ventricle. The prevalence of tricuspid regurgitation increased by 45%. Of 238 patients with normal RV function at Exam 1, 55 (23%) developed RVD during follow-up. Development of RVD was associated with both prevalent and incident atrial fibrillation (AF), higher body weight, coronary disease, higher pulmonary artery and left ventricular filling pressures, and RV dilation. Patients with HFpEF developing incident RVD had nearly two-fold increased risk of death (adjusted hazard ratio 1.89, 95% confidence interval 1.01-3.44; P = 0.04).

CONCLUSION

While previous attention has centred on the left ventricle in HFpEF, these data show that right ventricular structure and function deteriorate to greater extent over time when compared with changes in the left ventricle. Further study is required to evaluate whether interventions targeting modifiable risk factors identified for incident RVD, including abnormal haemodynamics, AF, coronary disease, and obesity, can prevent RVD and thus improve outcomes.

Zinc transporter ZIP13 suppresses beige adipocyte biogenesis and energy expenditure by regulating C/EBP-β expression

Given the relevance of beige adipocytes in adult humans, a better understanding of the molecular circuits involved in beige adipocyte biogenesis has provided new insight into human brown adipocyte biology. Genetic mutations in SLC39A13/ZIP13, a member of zinc transporter family, are known to reduce adipose tissue mass in humans; however, the underlying mechanisms remains unknown. Here, we demonstrate that the Zip13-deficient mouse shows enhanced beige adipocyte biogenesis and energy expenditure, and shows ameliorated diet-induced obesity and insulin resistance. Both gain- and loss-of-function studies showed that an accumulation of the CCAAT/enhancer binding protein-β (C/EBP-β) protein, which cooperates with dominant transcriptional co-regulator PR domain containing 16 (PRDM16) to determine brown/beige adipocyte lineage, is essential for the enhanced adipocyte browning caused by the loss of ZIP13. Furthermore, ZIP13-mediated zinc transport is a prerequisite for degrading the C/EBP-β protein to inhibit adipocyte browning. Thus, our data reveal an unexpected association between zinc homeostasis and beige adipocyte biogenesis, which may contribute significantly to the development of new therapies for obesity and metabolic syndrome.

Inducible brown fat-like cells, named beige adipocytes have recently been a topic of great interest, mainly because they are induced in response to external cues, and are closely associated with adult human brown adipocyte. Therefore, the identification of selective molecular circuits involved in beige adipocyte biogenesis and thermogenesis will enable the selective induction of white adipocyte browning as a therapy for obesity. Here, we show that zinc homeostasis, which is controlled by ZIP13, a protein associated with human disease, is essential for the accurate regulation of beige adipocyte differentiation. Inhibition of ZIP13 function enhances beige adipocyte biogenesis and thermogenesis, highlighting the potential of ZIP13 as a therapeutic target for obesity and metabolic syndrome.

Exploring the molecular mechanisms underlying α- and β-cell dysfunction in diabetes

Pancreatic islet dysfunction, including impaired insulin secretion in β cells and dysregulated glucagon secretion in α cells, is the chief pathology of diabetes. In β cells, oxidative stress, evoked by chronic hyperglycemia, was found to induce dysfunction of a critical transcription factor, PDX1, caused by its nucleocytoplasmic translocation via interactions with the insulin and JNK signaling pathways and another transcription factor, FOXO1. The significance of α-cell insulin signaling in the physiological and pathological regulation of α-cell biology was demonstrated in α-cell-specific insulin receptor knockout mice, which exhibited dysregulated glucagon secretion. Moreover, a high-glucose load directly induced excessive glucagon secretion in a glucagon-secreting cell line and isolated islets, together with impairment of insulin signaling. These findings indicate that disordered insulin signaling is central to the pathophysiology of islet dysfunction in both α and β cells. On the other hand, certain beneficial effects of GLP-1 on dysfunctional α and β cells indicate that it has therapeutic potential for diabetes patients who exhibit insulin resistance in islets. These studies, involving basic medical research approaches, have-at least in part-clarified the molecular mechanisms underlying α- and β-cell dysfunction in diabetes, and offer important clues that should aid the development of future therapeutic approaches to the disease.

Sexual dimorphisms of mRNA and miRNA in human/murine heart disease

BACKGROUND

Sexual dimorphisms are well recognized in various cardiac diseases such as ischemic cardiomyopathy (ICM), hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). Thorough understanding of the underlying genetic programs is crucial to optimize treatment strategies specified for each gender. By performing meta-analysis and microarray analysis, we sought to comprehensively characterize the sexual dimorphisms in the healthy and diseased heart at the level of both mRNA and miRNA transcriptome.

RESULTS

Existing mRNA microarray data of both mouse and human heart were integrated, identifying dozens/ hundreds of sexually dimorphic genes in healthy heart, ICM, HCM, and DCM. These sexually dimorphic genes overrepresented gene ontologies (GOs) important for cardiac homeostasis. Further, microarray of miRNA, isolated from mouse sham left ventricle (LV) (n = 6 & n = 5 for male & female) and chronic MI LV (n = 19 & n = 19) and from human normal LV (n = 6 & n = 6) and ICM LV (n = 4 & n = 5), was conducted. This revealed that 13 mouse miRNAs are sexually dimorphic in MI and 6 in normal heart. In human, 3 miRNAs were sexually dimorphic in ICM and 15 in normal heart. These data revealed miRNA-mRNA networks that operate in a sexually-biased fashion.

CONCLUSIONS

mRNA and miRNA transcriptome of normal and disease heart show significant sex differences, which might impact the cardiac homeostasis. Together this study provides the first comprehensive picture of the genome-wide program underlying the heart sexual dimorphisms, laying the foundation for gender specific treatment strategies.

Involvement of Band3 in the efflux of sphingosine 1-phosphate from erythrocytes

Sphingosine 1-phosphate (S1P) is a bioactive lipid mediator that is thought to be involved in various diseases. Although the main source of S1P in the plasma is erythrocytes, how S1P is exported from erythrocytes has not been elucidated. When we differentiated K562 cells into erythroblast-like cells with sodium butyrate, we observed that the efflux of S1P was increased without increased expression of previously proposed S1P transporters, while the expression levels of Band3 were increased. Therefore, in this study, we investigated the involvement of Band 3, the most characteristic membranous transporter for erythrocytes, in S1P efflux, using 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid, disodium salt (H2DIDS), which is an inhibitor of Band3. First, we treated human washed erythrocytes with H₂DIDS and found that H₂DIDS decreased the S1P levels in the supernatant, while it increased the cellular S1P contents. Next, when we injected H₂DIDS into mice, the plasma S1P level was significantly decreased. Finally, when we overexpressed or suppressed Band3 in K562 cells, S1P efflux was enhanced or decreased, respectively, while the overexpression of Band3 in HEK293 cells did not modulate S1P efflux. These results suggested the possible involvement of Band3 in the transport of S1P, a multi-functional bioactive phospholipid, from erythrocytes.

Obesity-induced DNA released from adipocytes stimulates chronic adipose tissue inflammation and insulin resistance

Obesity stimulates chronic inflammation in adipose tissue, which is associated with insulin resistance, although the underlying mechanism remains largely unknown. Here we showed that obesity-related adipocyte degeneration causes release of cell-free DNA (cfDNA), which promotes macrophage accumulation in adipose tissue via Toll-like receptor 9 (TLR9), originally known as a sensor of exogenous DNA fragments. Fat-fed obese wild-type mice showed increased release of cfDNA, as determined by the concentrations of single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) in plasma. cfDNA released from degenerated adipocytes promoted monocyte chemoattractant protein-1 (MCP-1) expression in wild-type macrophages, but not in TLR9-deficient (Tlr9 (-/-) ) macrophages. Fat-fed Tlr9 (-/-) mice demonstrated reduced macrophage accumulation and inflammation in adipose tissue and better insulin sensitivity compared with wild-type mice, whereas bone marrow reconstitution with wild-type bone marrow restored the attenuation of insulin resistance observed in fat-fed Tlr9 (-/-) mice. Administration of a TLR9 inhibitory oligonucleotide to fat-fed wild-type mice reduced the accumulation of macrophages in adipose tissue and improved insulin resistance. Furthermore, in humans, plasma ssDNA level was significantly higher in patients with computed tomography-determined visceral obesity and was associated with homeostasis model assessment of insulin resistance (HOMA-IR), which is the index of insulin resistance. Our study may provide a novel mechanism for the development of sterile inflammation in adipose tissue and a potential therapeutic target for insulin resistance.

Autophagy: A Novel Therapeutic Target for Diabetic Nephropathy

Diabetic nephropathy is a leading cause of end stage renal disease and its occurance is increasing worldwide. The most effective treatment strategy for the condition is intensive treatment to strictly control glycemia and blood pressure using renin-angiotensin system inhibitors. However, a fraction of patients still go on to reach end stage renal disease even under such intensive care. New therapeutic targets for diabetic nephropathy are, therefore, urgently needed. Autophagy is a major catabolic pathway by which mammalian cells degrade macromolecules and organelles to maintain intracellular homeostasis. The accumulation of damaged proteins and organelles is associated with the pathogenesis of diabetic nephropathy. Autophagy in the kidney is activated under some stress conditions, such as oxidative stress and hypoxia in proximal tubular cells, and occurs even under normal conditions in podocytes. These and other accumulating findings have led to a hypothesis that autophagy is involved in the pathogenesis of diabetic nephropathy. Here, we review recent findings underpinning this hypothesis and discuss the advantages of targeting autophagy for the treatment of diabetic nephropathy.