Hepatocyte-derived DPP4 regulates portal GLP-1 bioactivity, modulates glucose production, and when absent influences NAFLD progression

Elevated circulating dipeptidyl peptidase-4 (DPP4) is a biomarker for liver disease, but its involvement in gluconeogenesis and metabolic associated fatty liver disease progression remains unclear. Here, we identified that DPP4 in hepatocytes but not TEK receptor tyrosine kinase-positive endothelial cells regulates the local bioactivity of incretin hormones and gluconeogenesis. However, the complete absence of DPP4 (Dpp4-/-) in aged mice with metabolic syndrome accelerates liver fibrosis without altering dyslipidemia and steatosis. Analysis of transcripts from the livers of Dpp4-/- mice displayed enrichment for inflammasome, p53, and senescence programs compared with littermate controls. High-fat, high-cholesterol feeding decreased Dpp4 expression in F4/80+ cells, with only minor changes in immune signaling. Moreover, in a lean mouse model of severe nonalcoholic fatty liver disease, phosphatidylethanolamine N-methyltransferase mice, we observed a 4-fold increase in circulating DPP4, in contrast with previous findings connecting DPP4 release and obesity. Last, we evaluated DPP4 levels in patients with hepatitis C infection with dysglycemia (Homeostatic Model Assessment of Insulin Resistance > 2) who underwent direct antiviral treatment (with/without ribavirin). DPP4 protein levels decreased with viral clearance; DPP4 activity levels were reduced at long-term follow-up in ribavirin-treated patients; but metabolic factors did not improve. These data suggest elevations in DPP4 during hepatitis C infection are not primarily regulated by metabolic disturbances.

Abstract 531: Sex Differences In The Metabolic Switch From Fasting To Refeeding In The Murine Jejunum

Introduction: The small intestine receives hormonal and neuronal stimuli to ensure sufficient nutrient absorption to fuel the body. Insulin resistance promotes aberrant dietary fat delivery into circulation, increasing the risk of cardiovascular disease. The mechanisms underlying the loss of controlled dietary fat delivery during metabolic disease are unclear. We aimed to characterize the metabolic pathways engaged in the small intestine in the transition from fasting to refeeding states in both male and female mice.

Methods: Eight- to twelve-week-old male and female mice fasted for 24 hours. Half of the mice were euthanized in the fasted state, and the remaining half were euthanized after a 4-hour refeeding period (Teklad Global 19% Protein Extruded Diet). Gene expression and pathway analyses in jejunal samples were determined using Nanostring.

Results: In male and female mice, refeeding significantly upregulated pathways in amino acid synthesis, mitochondrial respiration, and proto-oncogene Myc signalling compared to fasting. Refeeding significantly downregulated glycolysis, and both mitogen-activated MAPK and PI3K signalling pathways compared to fasting. Interestingly, in males refeeding significantly upregulated AMPK, mTOR, and autophagy, whereas conversely in female mice, refeeding downregulated these pathways. Surprisingly, fatty acid synthesis and fatty acid oxidation pathways were unchanged by the nutritional state in males, but in females, both pathways were significantly downregulated with refeeding compared to fasting. In female mice, refeeding significantly reduced small intestinal length compared to fasting, whereas intestinal length was unchanged in male mice.

Conclusions: Metabolic pathways well-characterized in the liver are often mechanistically extrapolated to the gut. We have begun to uncover the jejunal gene expression changes regulated by nutrient availability in male and female mice. Identifying how high-fat feeding dysregulates these pathways will help further elucidate the mechanism underlying the over-production of intestinally-derived lipoproteins in metabolic disease.

Quantification of murine myocardial infarct size using 2-D and 4-D high-frequency ultrasound

Ischemic heart disease is the leading cause of death in the United States, Canada, and worldwide. Severe disease is characterized by coronary artery occlusion, loss of blood flow to the myocardium, and necrosis of tissue, with subsequent remodeling of the heart wall, including fibrotic scarring. The current study aims to demonstrate the efficacy of quantitating infarct size via two-dimensional (2-D) echocardiographic akinetic length and four-dimensional (4-D) echocardiographic infarct volume and surface area as in vivo analysis techniques. We further describe and evaluate a new surface area strain analysis technique for estimating myocardial infarction (MI) size after ischemic injury. Experimental MI was induced in mice via left coronary artery ligation. Ejection fraction and infarct size were measured through 2-D and 4-D echocardiography. Infarct size established via histology was compared with ultrasound-based metrics via linear regression analysis. Two-dimensional echocardiographic akinetic length (r = 0.76, P = 0.03), 4-D echocardiographic infarct volume (r = 0.85, P = 0.008), and surface area (r = 0.90, P = 0.002) correlate well with histology. Although both 2-D and 4-D echocardiography were reliable measurement techniques to assess infarct, 4-D analysis is superior in assessing asymmetry of the left ventricle and the infarct. Strain analysis performed on 4-D data also provides additional infarct sizing techniques, which correlate with histology (surface strain: r = 0.94, P < 0.001, transmural thickness: r = 0.76, P = 0.001). Two-dimensional echocardiographic akinetic length, 4-D echocardiography ultrasound, and strain provide effective in vivo methods for measuring fibrotic scarring after MI.NEW & NOTEWORTHY Our study supports that both 2-D and 4-D echocardiographic analysis techniques are reliable in quantifying infarct size though 4-D ultrasound provides a more holistic image of LV function and structure, especially after myocardial infarction. Furthermore, 4-D strain analysis correctly identifies infarct size and regional LV dysfunction after MI. Therefore, these techniques can improve functional insight into the impact of pharmacological interventions on the pathophysiology of cardiac disease.