SGLT2 inhibition leads to a restoration of hepatic and circulating metabolites involved in the folate cycle and pyrimidine biosynthesis.

Inhibition of sodium-glucose cotransporter 2 (SGLT2) by empagliflozin (EMPA) and other "flozins" can improve glycemic control under conditions of diabetes and kidney disease. Though they act on the kidney, they also offer cardiovascular and liver protection. Previously, we found that EMPA decreased circulating triglycerides and hepatic lipid and cholesterol esters in male TallyHo mice fed a high-milk-fat diet (HMFD). The goal of this study was to determine whether the liver protection is associated with a change in metabolic function by characterizing the hepatic and circulating metabolic and lipidomic profiles using targeted LC-MS. In both male and female mice, HMFD feeding significantly altered the circulating and hepatic metabolome compared with low-fat diet (LFD). Addition of EMPA resulted in the restoration of circulating orotate (intermediate in pyrimidine biosynthesis) and hepatic dihydrofolate (intermediate in the folate and methionine cycles) levels in males and acylcarnitines in females. These changes were partially explained by altered expression of rate-limiting enzymes in these pathways. This metabolic signature was not detected when EMPA was incorporated into an LFD, suggesting that the restoration requires the metabolic shift that accompanies the HMFD. Notably, the HMFD increased expression of 18 of 20 circulating amino acids in males and 11 of 20 in females, and this pattern was reversed by EMPA. Finally, we confirmed that SGLT2 inhibition upregulates ketone bodies including ß-hydroxybutyrate. Collectively, this study highlights the metabolic changes that occur with EMPA treatment, and sheds light on the possible mechanisms by which this drug offers liver and systemic protection.NEW & NOTEWORTHY Sodium-glucose cotransporter 2 (SGLT2) inhibitors, including empagliflozin, have emerged as a new treatment option for individuals with type 2 diabetes that have positive impacts on kidney and cardiovascular disease. However, less is known about their impact on other tissues, including the liver. Here, we report that empagliflozin reduces hepatic steatosis that is associated with restoring metabolic intermediates in the folate and pyrimidine biosynthesis pathways. These changes may lead to new approaches to treat nonalcoholic fatty liver disease.

Tachol1 QTL on mouse chromosome 1 is responsible for hypercholesterolemia and diet-induced obesity.

Hypercholesterolemia raises the risk for cardiovascular complications and overall health. Hypercholesterolemia is common, affecting 10% of the general population of the US, and heritable. Most individuals with hypercholesterolemia have a polygenic predisposition to the condition. Previously we identified a quantitative trait locus, Tachol1, linked to hypercholesterolemia on mouse chromosome 1 (Chr1) in a cross between C57BL/6J (B6) and TALLYHO/JngJ (TH) mice, a polygenic model for human obesity, type 2 diabetes and hyperlipidemia. Subsequently, using congenic mice that carry a TH-derived genomic segment of Chr1 on a B6 background, we demonstrated that the distal segment of Chr1, where Tachol1 maps, is necessary to cause hypercholesterolemia, as well as diet-induced obesity. In this study, we generated overlapping subcongenic lines to the distal segment of congenic region and characterized subcongenic mice carrying the smallest TH region of Tachol1, ~ 16.2 Mb in size (B6.TH-Chr1-16.2 Mb). Both male and female B6.TH-Chr1-16.2 Mb mice showed a significantly increased plasma total cholesterol levels compared to B6 on both chow and high fat (HF) diet. B6.TH-Chr1-16.2 Mb mice also had greater fat mass than B6 on HF diet, without increasing food intake. The gene and protein expression levels of absent in melanoma 2 (Aim2) gene were significantly upregulated in B6.TH-Chr1-16.2 Mb mice compared to B6. In summary, we confirmed the effect of Tachol1 on hypercholesterolemia and diet-induced obesity using subcongenic analysis.

High Glucose Levels Promote Switch to Synthetic Vascular Smooth Muscle Cells via Lactate/GPR81.

Hyperglycemia, lipotoxicity, and insulin resistance are known to increase the secretion of extracellular matrix from cardiac fibroblasts as well as the activation of paracrine signaling from cardiomyocytes, immune cells, and vascular cells, which release fibroblast-activating mediators. However, their influences on vascular smooth muscle cells (vSMCs) have not been well examined. This study aimed to investigate whether contractile vascular vSMCs could develop a more synthetic phenotype in response to hyperglycemia. The results showed that contractile and synthetic vSMCs consumed high glucose in different ways. Lactate/GPR81 promotes the synthetic phenotype in vSMCs in response to high glucose levels. The stimulation of high glucose was associated with a significant increase in fibroblast-like features: synthetic vSMC marker expression, collagen 1 production, proliferation, and migration. GPR81 expression is higher in blood vessels in diabetic patients and in the high-glucose, high-lipid diet mouse. The results demonstrate that vSMCs assume a more synthetic phenotype when cultured in the presence of high glucose and, consequently, that the high glucose could trigger a vSMC-dependent cardiovascular disease mechanism in diabetes via lactate/GPR81.

Utility and Limitations of TALLYHO/JngJ as a Model for Type 2 Diabetes-Induced Bone Disease.

Type 2 diabetes mellitus (T2DM) increases risk of fractures due to bone microstructural and material deficits, though the mechanisms remain unclear. Preclinical models mimicking diabetic bone disease are required to further understand its pathogenesis. The TALLYHO/JngJ (TH) mouse is a polygenic model recapitulating adolescent-onset T2DM in humans. Due to incomplete penetrance of the phenotype ~25% of male TH mice never develop hyperglycemia, providing a strain-matched nondiabetic control. We performed a comprehensive characterization of the metabolic and skeletal phenotype of diabetic TH mice and compared them to either their nondiabetic TH controls or the recommended SWR/J controls to evaluate their suitability to study diabetic bone disease in humans. Compared to both controls, male TH mice with T2DM exhibited higher blood glucose levels, weight along with impaired glucose tolerance and insulin sensitivity. TH mice with/without T2DM displayed higher cortical bone parameters and lower trabecular bone parameters in the femurs and vertebrae compared to SWR/J. The mechanical properties remained unchanged for all three groups except for a low-energy failure in TH mice with T2DM only compared to SWR/J. Histomorphometry analyses only revealed higher number of osteoclasts and osteocytes for SWR/J compared to both groups of TH. Bone turnover markers procollagen type 1 N-terminal propeptide (P1NP) and tartrate-resistant acid phosphatase (TRAP) were low for both groups of TH mice compared to SWR/J. Silver nitrate staining of the femurs revealed low number of osteocyte lacunar and dendrites in TH mice with T2DM. Three-dimensional assessment showed reduced lacunar parameters in trabecular and cortical bone. Notably, osteocyte morphology changed in TH mice with T2DM compared to SWR/J. In summary, our study highlights the utility of the TH mouse to study T2DM, but not necessarily T2DM-induced bone disease, as there were no differences in bone strength and bone cell parameters between diabetic and non-diabetic TH mice. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.