Loss of hepatic PPARα in mice causes hypertension and cardiovascular disease

Abstract

The leading cause of death in patients with non-alcoholic fatty liver disease (NAFLD) is cardiovascular disease (CVD). However, the mechanisms are unknown. Mice deficient in hepatocyte PPARα ( PparaHepKO) exhibit hepatic steatosis on a regular diet, making them prone to manifesting NAFLD. We hypothesized that the PparaHepKO mice might be predisposed to poorer cardiovascular phenotypes due to increased liver fat content. We use PparaHepKO and littermate control mice fed a regular chow diet to avoid complications with a high-fat diet, such as insulin resistance and increased adiposity. After 30 weeks on a standard diet, male PparaHepKO mice exhibited elevated hepatic fat content compared to littermates as measured by Echo MRI (11.95 ± 1.4 vs. 3.74 ± 1.4%, p<0.05), hepatic triglycerides (1.4 ± 0.10 vs. 0.3 ± 0.01mM, p<0.05), and Oil Red O staining, despite no changes in body weight, fasting blood glucose, and insulin. The PparaHepKO mice also displayed elevated mean arterial blood pressure (121 ± 4 vs. 108 ± 2 mmHg, p<0.05), impaired diastolic function, cardiac remodeling, and enhanced vascular stiffness. To determine mechanisms controlling the increase in stiffness in the aorta, we used state-of-the-art PamGene technology to measure kinase activity. Our data suggest that the loss of hepatic PPARα induces alterations in the aortas that reduce the kinase activity of tropomyosin receptor kinases (TRKs) and p70S6K kinase, which might contribute to the pathogenesis of NAFLD-induced CVD. These data indicate that hepatic PPARα protects the cardiovascular system through some as-of-yet undefined mechanism.

Cardiac lipotoxicity and fibrosis underlie impaired contractility in a mouse model of metabolic dysfunction‐associated steatotic liver disease

“…These mice exhibit hepatic steatosis in the absence of obesity, insulin resistance, and alterations in plasma triglycerides and lipids. 13 We observed that the Ppara HepKO mice are also hypertensive, and exhibit left ventricular remodeling with altered cardiac function and vascular stiffness. 13 Thus, this mouse model provides an opportunity to examine the impact of MASLD on the cardiovascular system, including the heart, in the absence of confounding effects of obesity and obesity‐associated metabolic abnormalities.…”

“… 13 We observed that the Ppara HepKO mice are also hypertensive, and exhibit left ventricular remodeling with altered cardiac function and vascular stiffness. 13 Thus, this mouse model provides an opportunity to examine the impact of MASLD on the cardiovascular system, including the heart, in the absence of confounding effects of obesity and obesity‐associated metabolic abnormalities. The present study was designed to determine the mechanisms responsible for the alterations in cardiac function in Ppara HepKO mice.…”

“…Ppara HepKO and hepatocyte‐specific peroxisome proliferator‐activated receptor alpha flox/flox ( Ppara fl/fl ) mice were bred in our colony at the University of Mississippi Medical Center as previously described. 13 , 14 The standard mouse chow consisted of 17% fat (Teklad diet, #8604, Harland Laboratories, Inc., Indianapolis, IN). Studies were performed on 30‐week‐old male mice.…”

“…Western blots were performed on cardiac and liver samples (30 μg) as we previously described. 13 , 14 , 18 Membranes were incubated overnight at 4°C with the following antibodies: ANP (1:1000, Abcam, ab180649), BNP (1:1000, Santa Cruz Biotechnology, sc‐271185), cleaved anti‐caspase‐3 (1:1000, Cell Signaling Technology, #9661), Pro‐caspase‐3 (1:1000, NovusBio, B‐6), B‐cell lymphoma protein 2 (BCl‐2) (1:1000, Santa Cruz Biotechnology, sc‐7382), B‐cell lymphoma protein 2‐associated X (BAX) (1:1000, Invitrogen, YB3837921), D‐β‐hydroxybutyrate dehydrogenase I (BDH1) (1:2000,15417, Thermofisher), and heat shock protein 90 (1:5000, Santa Cruz Biotechnology, sc‐13119). After three washes in TBS + 0.1% Tween 20, the membrane was incubated with an infrared donkey anti‐goat (IRDye 800LI‐COR Biosciences, 926‐32214) or donkey anti‐rabbit (IRDye 800LI‐COR Biosciences, 926‐32214) or goat anti‐mouse (IRDye 680, LI‐COR Biosciences, 926‐68020) secondary antibody (LI‐COR Biosciences) (1:2,000 dilution in TBS) for 2 hrs at 4°C.…”

“… 10 , 12 Notably, emerging findings have revealed that cardiac lipotoxicity is a vital risk factor for development of heart failure with preserved ejection fraction often observed in patients with MASLD. 13 …”