Amplification of lipotoxic cardiomyopathy in the VDR gene knockout mouse.

Previous studies demonstrated that the liganded vitamin D receptor (VDR) plays an important role in controlling cardiovascular homeostasis. Both the whole animal VDR gene knockout (VDR-/-) and the myocyte-specific VDR gene deletion result in changes in cardiac structure and function. Clinical states associated with cardiac steatosis (obesity and diabetes mellitus) are also associated with low circulating 25 OH vitamin D levels. We, therefore, examined the effects of VDR deficiency (VDR-/- mouse) in a murine model of cardiac steatosis that expresses the terminal enzyme involved in triglyceride synthesis, diacylglycerol acyltransferase 1 (DGAT1), selectively in the cardiac myocyte. These mice display early cardiac dysfunction and late cardiomyopathy and heart failure. In the present study, we demonstrate that mice harboring both genetic modifications (i.e., MHC-DGAT1 Tg and VDR-/-) exhibit an increase in myocyte size, heart weight/body weight ratio and natriuretic peptide gene expression, all markers of cardiac hypertrophy, that exceed that seen in either VDR-/- or the MHC-DGAT1 Tg mice alone. This was accompanied by a dramatic increase in interstitial fibrosis and increased expression of collagen 1a1 and collagen 3a1, as well as the osteopontin and matrix metalloproteinase 2, genes. At a functional level, this resulted in a 37% reduction in ejection fraction and 55% reduction in fractional shortening in the DGAT1; VDR-/- mice relative to the controls. Collectively, these data demonstrate that deficiency in the vitamin D signaling system enhances the pathological phenotype in this experimental cardiomyopathy and suggest an important role for vitamin D in modulating disease severity in common cardiovascular disorders.

Cardiac steatosis potentiates angiotensin II effects in the heart.

Lipid accumulation in the heart is associated with obesity and diabetes and may play an important role in the pathogenesis of heart failure. The renin-angiotensin system is also thought to contribute to cardiovascular morbidity in obese and diabetic patients. We hypothesized that the presence of lipid within the myocyte might potentiate the cardiomyopathic effects of ANG II in the cardiac diacylglycerol acyl transferase 1 (DGAT1) transgenic mouse model of myocyte steatosis. Treatment with ANG II resulted in a similar increase in blood pressure in both nontransgenic and DGAT1 transgenic mice. However, ANG II in DGAT1 transgenic mice resulted in a marked increase in interstitial fibrosis and a reduction in systolic function compared with nontransgenic littermates. Lipidomic analysis revealed that >20% of lipid species were significantly altered between nontransgenic and DGAT1 transgenic animals, whereas 3% were responsive to ANG II administration. ROS were also increased by ANG II in DGAT1 transgenic hearts. ANG II treatment resulted in increased expression of transforming growth factor (TGF)-ß2 and the type I TGF-ß receptor as well as increased phosphorylation of Smad2 in DGAT1 transgenic hearts. Injection of neutralizing antibodies to TGF-ß resulted in a reduction in fibrosis in DGAT1 transgenic hearts treated with ANG II. These results suggest that myocyte steatosis amplifies the fibrotic effects of ANG II through mechanisms that involve activation of TGF-ß signaling and increased production of ROS.

Effect of combining an ACE inhibitor and a VDR activator on glomerulosclerosis, proteinuria, and renal oxidative stress in uremic rats.

Angiotensin-converting enzyme (ACE) inhibitors ameliorate the progression of renal disease. In combination with vitamin D receptor activators, they provide additional benefits. In the present study, uremic (U) rats were treated as follows: U+vehicle (UC), U+enalapril (UE; 25 mg/l in drinking water), U+paricalcitol (UP; 0.8 µg/kg ip, 3 × wk), or U+enalapril+paricalcitol (UEP). Despite hypertension in UP rats, proteinuria decreased by 32% vs. UC rats. Enalapril alone, or in combination with paricalcitol, further decreased proteinuria (≈70%). Glomerulosclerosis and interstitial infiltration increased in UC rats. Paricalcitol and enalapril inhibited this. The increase in cardiac atrial natriuretic peptide (ANP) seen in UC rats was significantly decreased by paricalcitol. Enalapril produced a more dramatic reduction in ANP. Renal oxidative stress plays a critical role in inflammation and progression of sclerosis. The marked increase in p22(phox), a subunit of NADPH oxidase, and decrease in endothelial nitric oxide synthase were inhibited in all treated groups. Cotreatment with both compounds inhibited the uremia-induced increase in proinflammatory inducible nitric oxide synthase (iNOS) and glutathione peroxidase activity better than either compound alone. Glutathione reductase was also increased in UE and UP rats vs. UC. Kidney 4-hydroxynonenal was significantly increased in the UC group compared with the normal group. Combined treatment with both compounds significantly blunted this increase, P < 0.05, while either compound alone had no effect. Additionally, the expression of Mn-SOD was increased and CuZn-SOD decreased by uremia. This was ameliorated in all treatment groups. Cotreatment with enalapril and paricalcitol had an additive effect in increasing CuZn-SOD expression. In conclusion, like enalapril, paricalcitol alone can improve proteinuria, glomerulosclerosis, and interstitial infiltration and reduce renal oxidative stress. The effects of paricalcitol may be amplified when an ACE inhibitor is added since cotreatment with both compounds seems to have an additive effect on ameliorating uremia-induced changes in iNOS and CuZn-SOD expression, peroxidase activity, and renal histomorphometry.