Estrogen-Related Receptor Agonism Reverses Mitochondrial Dysfunction and Inflammation in the Aging Kidney

A gradual decline in renal function occurs even in healthy aging individuals. In addition to aging, per se, concurrent metabolic syndrome and hypertension, which are common in the aging population, can induce mitochondrial dysfunction and inflammation, which collectively contribute to age-related kidney dysfunction and disease. This study examined the role of the nuclear hormone receptors, the estrogen-related receptors (ERRs), in regulation of age-related mitochondrial dysfunction and inflammation. The ERRs were decreased in both aging human and mouse kidneys and were preserved in aging mice with lifelong caloric restriction (CR). A pan-ERR agonist, SLU-PP-332, was used to treat 21-month-old mice for 8 weeks. In addition, 21-month-old mice were treated with a stimulator of interferon genes (STING) inhibitor, C-176, for 3 weeks. Remarkably, similar to CR, an 8-week treatment with a pan-ERR agonist reversed the age-related increases in albuminuria, podocyte loss, mitochondrial dysfunction, and inflammatory cytokines, via the cyclic GMP-AMP synthase-STING and STAT3 signaling pathways. A 3-week treatment of 21-month-old mice with a STING inhibitor reversed the increases in inflammatory cytokines and the senescence marker, p21/cyclin dependent kinase inhibitor 1A (Cdkn1a), but also unexpectedly reversed the age-related decreases in PPARG coactivator (PGC)-1α, ERRα, mitochondrial complexes, and medium chain acyl coenzyme A dehydrogenase (MCAD) expression. These studies identified ERRs as CR mimetics and as important modulators of age-related mitochondrial dysfunction and inflammation. These findings highlight novel druggable pathways that can be further evaluated to prevent progression of age-related kidney disease.

Susceptibility of female rats to cardiac arrhythmias following refeeding after severe food restriction

Background

Many studies have shown malnutrition and inadequate caloric consumption have adverse acute effects on cardiovascular structure and function.

Methods

To determine the adverse long term cardiovascular effects, we studied cardiac morphology and function in female (F) and male (M) severe food restricted rats 3 months after refeeding (sFR-Refed).

Results

Two weeks of a normal chow diet in which calories were reduced by 60% decreased body weight (BW) by approximately 15% in both sexes. Within 2 weeks of refeeding, no differences in BW were detected between CT and sFR-Refed groups. However, male rats gained almost 3 times more BW than the females over the 3-month refeeding period. Sex differences were also observed in cardiac pathology. Hearts from F-sFR-Refed rats exhibited more atrophy and less hypertrophy, while M-sFR-Refed rats predominantly exhibited hypertrophic remodeling. While there were no differences in the frequency of ventricular arrhythmias induced by ischemia/reperfusion (I/R) in the isolated heart between M-CT and M-sFR-Refed rats, I/R induced twice as many arrhythmias in the F-sFR-Refed rats compared to F-CT.

Conclusions

These findings indicate the female heart is more susceptible to the long term adverse cardiovascular effects of sFR months after refeeding. Thus, this study provides a rationale for studying sex differences in cardiovascular risk in individuals who experience sFR for voluntary (e.g., very low-calorie dieting) or involuntary (e.g., poverty) reasons earlier in life.

What are the long-term effects of a 2-week period of severe food restriction (sFR) on cardiac structure and function months after refeeding (sFR-Refed) in male and female rats?

This study shows sex differences exist in cardiac pathology months after refeeding. A majority of cardiomyocytes were atrophied in F-sFR-Refed rats, while in M-sFR-Refed rats, the cardiomyocytes predominantly exhibited hypertrophic remodeling.

While there were no differences in the frequency of ventricular arrhythmias induced by ischemia/reperfusion (I/R) in the isolated heart between M-CT and M-sFR-Refed rats, I/R induced twice as many arrhythmias in the F-sFR-Refed rats compared to the controls.

Our findings have implications for the long-term risk of developing cardiovascular disease in individuals who have voluntarily or involuntarily experienced periods of sFR earlier in their lives, and that woman may be at greater cardiovascular risk than men.

Short-term very low caloric intake causes endothelial dysfunction and increased susceptibility to cardiac arrhythmias and pathology in male rats

New Findings

What is the central question of this study?

What are the effects of a 2 week period of severe food restriction on vascular reactivity of resistance arteries and on cardiac structure and function?

What is the main finding and its importance?

This study showed, for the first time, that a 2 week period of severe food restriction in adult male Fischer rats caused endothelial dysfunction in mesenteric arteries and increased the susceptibility to ischaemia–reperfusion‐induced arrhythmias and cardiac pathology. Our findings might have ramifications for cardiovascular risk in people who experience periods of inadequate caloric intake.

Abstract

Severe food restriction (sFR) is a common dieting strategy for rapid weight loss. Male Fischer rats were maintained on a control (CT) or sFR (40% of CT food intake) diet for 14 days to mimic low‐calorie crash diets. The sFR diet reduced body weight by 16%. Haematocrits were elevated by 10% in the sFR rats, which was consistent with the reduced plasma volume. Mesenteric arteries from sFR rats had increased sensitivity to vasoconstrictors, including angiotensin II [maximum (%): CT, 1.30 ± 0.46 versus sFR, 11.5 ± 1.6; P < 0.0001; n = 7] and phenylephrine [maximum (%): CT, 78.5 ± 2.8 versus sFR, 94.5 ± 1.7; P < 0.001; n = 7] and reduced sensitivity to the vasodilator acetylcholine [EC₅₀ (nm): CT, 49.2 ± 5.2 versus sFR, 71.6 ± 6.8; P < 0.05; n = 7]. Isolated hearts from sFR rats had a 1.7‐fold increase in the rate of cardiac arrhythmias in response to ischaemia–reperfusion and more cardiac pathology, including myofibrillar disarray with contractions and cardiomyocyte lysis, than hearts from CT rats. The sFR dietary regimen is similar to very low‐calorie commercial and self‐help weight‐loss programmes, which provide ∼800–1000 kcal day⁻¹. Therefore, these findings in rats warrant the study of cardiovascular function in individuals who engage in extreme dieting or are subjected to bouts of very low caloric intake for other reasons, such as socioeconomic factors and natural disasters.