Pioglitazone Inhibits Diabetes-Induced Atrial Mitochondrial Oxidative Stress and Improves Mitochondrial Biogenesis, Dynamics, and Function Through the PPAR-γ/PGC-1α Signaling Pathway.

Zhiwei Zhang,Gary Tse,Yungang Zhao,Mengqi Gong,Xinghua Wang,Tong Liu,Lei Meng,Jian Li,Yajuan Yang,Ya Suo,Ning Jiang,Jiuchun Qiu,Wen Shi,Xue Liang,Guangping Li,Xiaowei Zhang,Jianping Zhao

doi:10.3389/fphar.2021.658362

Abstract

Background: Oxidative stress contributes to adverse atrial remodeling in diabetes mellitus. This remodeling can be prevented by the PPAR-γ agonist pioglitazone via its antioxidant and anti-inflammatory effects. In this study, we examined the molecular mechanisms underlying the protective effects of pioglitazone on atrial remodeling in a rabbit model of diabetes. Methods: Rabbits were randomly divided into control, diabetic, and pioglitazone-treated diabetic groups. Echocardiographic, hemodynamic, and electrophysiological parameters were measured. Serum PPAR-γ levels, serum and tissue oxidative stress and inflammatory markers, mitochondrial morphology, reactive oxygen species (ROS) production rate, respiratory function, and mitochondrial membrane potential (MMP) levels were measured. Protein expression of the pro-fibrotic marker TGF-β1, the PPAR-γ coactivator-1α (PGC-1α), and the mitochondrial proteins (biogenesis-, fusion-, and fission-related proteins) was measured. HL-1 cells were transfected with PGC-1α small interfering RNA (siRNA) to determine the underlying mechanisms of pioglitazone improvement of mitochondrial function under oxidative stress. Results: The diabetic group demonstrated a larger left atrial diameter and fibrosis area than the controls, which were associated with a higher incidence of inducible atrial fibrillation (AF). The lower serum PPAR-γ level was associated with lower PGC-1α and higher NF-κB and TGF-β1 expression. Lower mitochondrial biogenesis (PGC-1α, NRF1, and TFAM)-, fusion (Opa1 and Mfn1)-, and fission (Drp1)-related proteins were detected. Mitochondrial swelling, higher mitochondrial ROS, lower respiratory control rate, and lower MMP were observed. The pioglitazone group showed a reversal of structural remodeling and a lower incidence of inducible AF, which were associated with higher PPAR-γ and PGC-1α. The pioglitazone group had lower NF-κB and TGF-β1 expression levels, whereas biogenesis-, fusion-, and fission-related protein expression was higher. Further, mitochondrial structure and function were improved. In HL-1 cells, PGC-1α siRNA transfection blunted the effect of pioglitazone on Mn-SOD protein expression and MMP collapse in H2O2-treated cells. Conclusion: Diabetes mellitus induces adverse atrial structural, electrophysiological remodeling, and mitochondrial damage and dysfunction. Pioglitazone prevented these abnormalities through the PPAR-γ/PGC-1α pathway.

Highlights

Atrial fibrillation (AF) is the most prevalent sustained cardiac arrhythmia observed in clinical practice, and its prevalence increases with increasing age and is associated with increased morbidity and mortality (Chugh et al, 2014)
Values are mean ± SEM; HR, heart rate; SBP, systolic blood pressure; DBP, diastolic blood pressure; MBP, mean blood pressure; LV enddiastolic pressure (LVEDP), left ventricular end diastolic presssure; + dp/ dtmax, maximal increasing rate of left intraventricular pressure; - dp/dtmax, maximal decreasing rate of left intraventricular pressure; LA diameter (LAD), left atrial diameter; IVS, interventricular septa; LV posterior wall (LVPW), left ventricular posterior wall; LVEDD, left ventricular end-diastolic dimension; LVESD, left ventricular end-systolic dimension; LV ejection fraction (LVEF), left ventricular ejection fraction. *Compared with the C group, p < 0.05; **compared with the C group, p < 0.01; #compared with the Diabetic group, p < 0.05
The main findings of the present study are 1) pioglitazone protected against diabetes-induced atrial structural and electrophysiological remodeling; 2) these proactive effects were associated with decreased transforming growth factor β1 (TGF-β1) protein expression, higher SOD activity, reduced atrial mitochondrial reactive oxygen species (ROS) production, and suppressed oxidative and inflammatory marker expression in serum (8-OHdG and hs-CRP) and LA (NF-κB) in diabetic rabbits; 3) pioglitazone ameliorated diabetes-induced atrial mitochondrial swelling, prevented mitochondrial respiratory dysfunction, and preserved MMP and alterations in biogenesis (PGC-1α, nuclear respiratory factor 1 (NRF1), and TFAM), fusion (Opa1 and mitofusin 1 (Mfn1)), and fission (Drp1)-related protein expression; and 4) pioglitazone mediates these beneficial effects through the peroxisome proliferatoractivated receptor γ (PPAR-γ)/PGC-1α signaling pathway (Figure 6E)

Summary

Introduction

Atrial fibrillation (AF) is the most prevalent sustained cardiac arrhythmia observed in clinical practice, and its prevalence increases with increasing age and is associated with increased morbidity and mortality (Chugh et al, 2014). Oxidative stress is mainly related to excessive production of reactive oxygen species (ROS). ROS can react with multiple cellular components (i.e., lipids, proteins, and DNA) and is associated with DNA damage, apoptosis, and cardiac hypertrophy and fibrosis (Finkel and Holbrook, 2000). Excessive ROS production damages mitochondrial proteins and DNA, leading to the disruption of ATP production and other essential functions in the mitochondria (Bhatti et al, 2017). Oxidative stress contributes to adverse atrial remodeling in diabetes mellitus. This remodeling can be prevented by the PPAR-γ agonist pioglitazone via its antioxidant and anti-inflammatory effects. We examined the molecular mechanisms underlying the protective effects of pioglitazone on atrial remodeling in a rabbit model of diabetes

Methods

Results

Discussion

Conclusion