No abstract

ObjectivsCytokine-dependent activation of fibroblasts to myofibroblasts, a key event in fibrosis, is accompanied by phenotypic changes with increased secretory and contractile properties dependent on increased energy utilization, yet changes in the energetic profile of these cells are not fully described. We hypothesize that the TGF-β1-mediated transformation of myofibroblasts is associated with an increase in mitochondrial content and function when compared to naive fibroblasts.MethodsCultured NIH/3T3 mouse fibroblasts treated with TGF-β1, a profibrotic cytokine, or vehicle were assessed for transformation to myofibroblasts (appearance of α-smooth muscle actin [α-SMA] stress fibers) and associated changes in mitochondrial content and functions using laser confocal microscopy, Seahorse respirometry, multi-well plate reader and biochemical protocols. Expression of mitochondrial-specific proteins was determined using western blotting, and the mitochondrial DNA quantified using Mitochondrial DNA isolation kit.ResultsTreatment with TGF-β1 (5 ng/mL) induced transformation of naive fibroblasts into myofibroblasts with a threefold increase in the expression of α-SMA (6.85 ± 0.27 RU) compared to cells not treated with TGF-β1 (2.52 ± 0.11 RU). TGF-β1 exposure increased the number of mitochondria in the cells, as monitored by membrane potential sensitive dye tetramethylrhodamine, and expression of mitochondria-specific proteins; voltage-dependent anion channels (0.54 ± 0.05 vs. 0.23 ± 0.05 RU) and adenine nucleotide transporter (0.61 ± 0.11 vs. 0.22 ± 0.05 RU), as well as mitochondrial DNA content (530 ± 12 μg DNA/106 cells vs. 307 ± 9 μg DNA/106 cells in control). TGF-β1 treatment was associated with an increase in mitochondrial function with a twofold increase in baseline oxygen consumption rate (2.25 ± 0.03 vs. 1.13 ± 0.1 nmol O2/min/106 cells) and FCCP-induced mitochondrial respiration (2.87 ± 0.03 vs. 1.46 ± 0.15 nmol O2/min/106 cells).ConclusionsTGF-β1 induced differentiation of fibroblasts is accompanied by energetic remodeling of myofibroblasts with an increase in mitochondrial respiration and mitochondrial content.

Excessive cardiac fibrosis, characterized by increased collagen-rich extracellular matrix (ECM) deposition, is a major predisposing factor for mechanical and electrical dysfunction in heart failure (HF). The human ventricular fibroblast (hVF) remodeling mechanisms that cause excessive collagen deposition in HF are unclear, although reports suggest a role for intracellular free Ca2+ in fibrosis. Therefore, we determined the association of differences in cellular Ca2+ dynamics and collagen secretion/deposition between hVFs from failing and normal (control) hearts. Histology of left ventricle sections (Masson trichrome) confirmed excessive fibrosis in HF versus normal. In vitro, hVFs from HF showed increased secretion/deposition of soluble collagen in 48 h of culture compared with control [85.9±7.4 µg/106 cells vs 58.5±8.8 µg/106 cells, P<0.05; (Sircol™ assay)]. However, collagen gene expressions (COL1A1 and COL1A2; RT-PCR) were not different. Ca2+ imaging (fluo-3) of isolated hVFs showed no difference in the thapsigargin-induced intracellular Ca2+ release capacity (control 16±1.4% vs HF 17±1.1%); however, Ca2+ influx via store-operated Ca2+ entry/Ca2+ release-activated channels (SOCE/CRAC) was significantly (P≤0.05) greater in HF-hVFs (47±3%) compared with non-failing (35±5%). Immunoblotting for ICRAC channel components showed increased ORAI1 expression in HF-hVFs compared with normal without any difference in STIM1 expression. The Pearson's correlation coefficient for co-localization of STIM1/ORAI1 was significantly (P<0.01) greater in HF (0.5±0.01) than control (0.4±0.01) hVFs. The increase in collagen secretion of HF versus control hVFs was eliminated by incubation of hVFs with YM58483 (10 µM), a selective ICRAC inhibitor, for 48 h (66.78±5.87 µg/106 cells vs 55.81±7.09 µg/106 cells, P=0.27). In conclusion, hVFs from HF have increased collagen secretion capacity versus non-failing hearts and this is related to increase in Ca2+ entry via SOCE and enhanced expression of ORAI, the pore-forming subunit. Therapeutic inhibition of SOCE may reduce the progression of cardiac fibrosis/HF.

Abstract-Interleukin (IL)-6 induced vascular smooth muscle cell (VSMC) motility in a dose-dependent manner. In addition, IL-6 stimulated tyrosine phosphorylation of gp130, resulting in the recruitment and activation of STAT-3. IL-6 -induced VSMC motility was found to be dependent on activation of gp130/STAT-3 signaling. IL-6 also induced cyclin D1 expression in a time-and gp130/STAT-3-dependent manner in VSMCs. Suppression of cyclin D1 levels via the use of its small interfering RNA molecules inhibited IL-6 -induced VSMC motility. Furthermore, balloon injury induced IL-6 expression both at mRNA and protein levels in rat carotid artery. Balloon injury also caused increased STAT-3 phosphorylation and cyclin D1 expression, leading to smooth muscle cell migration from the media to the intimal region. Blockade of gp130/STAT-3 signaling via adenovirus-mediated expression of dngp130 or dnSTAT-3 attenuated balloon injury-induced STAT-3 phosphorylation and cyclin D1 induction, resulting in reduced smooth muscle cell migration from media to intima and decreased neointima formation. Together, these observations for the first time suggest that IL-6/gp130/STAT-3 signaling plays an important role in vascular wall remodeling particularly in the settings of postangioplasty and thereby in neointima formation. (Circ Res. 2007;100:807-816.)

Selective downregulation of mitochondrial electron transport chain activity and increased oxidative stress in human atrial fibrillation. Am J Physiol Heart Circ Physiol 311: H54 -H63, 2016. First published May 6, 2016 doi:10.1152/ajpheart.00699.2015Mitochondria are critical for maintaining normal cardiac function, and a deficit in mitochondrial energetics can lead to the development of the substrate that promotes atrial fibrillation (AF) and its progression. However, the link between mitochondrial dysfunction and AF in humans is still not fully defined. The aim of this study was to elucidate differences in the functional activity of mitochondrial oxidative phosphorylation (OXPHOS) complexes and oxidative stress in right atrial tissue from patients without (non-AF) and with AF (AF) who were undergoing open-heart surgery and were not significantly different for age, sex, major comorbidities, and medications. The overall functional activity of the electron transport chain (ETC), NADH:O2 oxidoreductase activity, was reduced by 30% in atrial tissue from AF compared with non-AF patients. This was predominantly due to a selective reduction in complex I (0.06 Ϯ 0.007 vs. 0.09 Ϯ 0.006 nmol·min Ϫ1 ·citrate synthase activity Ϫ1 , P ϭ 0.02) and II (0.11 Ϯ 0.012 vs. 0.16 Ϯ 0.012 nmol·min Ϫ1 ·citrate synthase activity Ϫ1 , P ϭ 0.003) functional activity in AF patients. Conversely, complex V activity was significantly increased in AF patients (0.21 Ϯ 0.027 vs. 0.12 Ϯ 0.01 nmol·min Ϫ1 ·citrate synthase activity Ϫ1 , P ϭ 0.005). In addition, AF patients exhibited a higher oxidative stress with increased production of mitochondrial superoxide (73 Ϯ 17 vs. 11 Ϯ 2 arbitrary units, P ϭ 0.03) and 4-hydroxynonenal level (77.64 Ϯ 30.2 vs. 9.83 Ϯ 2.83 ng·mg Ϫ1 protein, P ϭ 0.048). Our findings suggest that AF is associated with selective downregulation of ETC activity and increased oxidative stress that can contribute to the progression of the substrate for AF. atrial fibrillation; humans; mitochondria; electron transport chain complexes; oxidative phosphorylation; oxidative stress; superoxide; 4-hydroxynonenal protein adducts NEW & NOTEWORTHYThe study provides evidence of a selective downregulation of mitochondrial electron transport chain functional activity predominantly affecting complexes I and II and associated increase ATRIAL FIBRILLATION (AF), a rapid irregular rhythm of the atria, is associated with electrical, functional, and structural changes in the atria that promote the substrate for its recurrence and progression (36, 53, 60). The incidence and prevalence of AF increase with advancing age and aging-associated diseases such as hypertension, ischemic heart disease, and heart failure (2, 40) and contribute to increased morbidity, particularly an increased risk for stroke, heart failure, and death (25,52). Although the pathophysiology of AF has been well characterized, the underlying mechanisms that contribute to the progression of AF in human atria have not been fully defined (33,35,57,58,60). Mitochondria, occupying 30% ...

AimsFibroblast to myofibroblast trans‐differentiation with altered bioenergetics precedes cardiac fibrosis (CF). Either prevention of differentiation or promotion of de‐differentiation could mitigate CF‐related pathologies. We determined whether 3‐hydroxy‐3‐methyl‐glutaryl‐coenzyme A (HMG‐CoA) reductase inhibitors—statins, commonly prescribed to patients at risk of heart failure (HF)—can de‐differentiate myofibroblasts, alter cellular bioenergetics, and impact the human ventricular fibroblasts (hVFs) in HF patients.Methods and resultsEither in vitro statin treatment of differentiated myofibroblasts (n = 3–6) or hVFs, isolated from human HF patients under statin therapy (HF + statin) vs. without statins (HF) were randomly used (n = 4–12). In vitro, hVFs were differentiated by transforming growth factor‐β1 (TGF‐β1) for 72 h (TGF‐72 h). Differentiation status and cellular oxygen consumption rate (OCR) were determined by α‐smooth muscle actin (α‐SMA) expression and Seahorse assay, respectively. Data are mean ± SEM except Seahorse (mean ± SD); P < 0.05, considered significant. In vitro, statins concentration‐dependently de‐differentiated the myofibroblasts. The respective half‐maximal effective concentrations were 729 ± 13 nmol/L (atorvastatin), 3.6 ± 1 μmol/L (rosuvastatin), and 185 ± 13 nmol/L (simvastatin). Mevalonic acid (300 μmol/L), the reduced product of HMG‐CoA, prevented the statin‐induced de‐differentiation (α‐SMA expression: 31.4 ± 10% vs. 58.6 ± 12%). Geranylgeranyl pyrophosphate (GGPP, 20 μmol/L), a cholesterol synthesis‐independent HMG‐CoA reductase pathway intermediate, completely prevented the statin‐induced de‐differentiation (α‐SMA/GAPDH ratios: 0.89 ± 0.05 [TGF‐72 h + 72 h], 0.63 ± 0.02 [TGF‐72 h + simvastatin], and 1.2 ± 0.08 [TGF‐72 h + simvastatin + GGPP]). Cellular metabolism involvement was observed when co‐incubation of simvastatin (200 nmol/L) with glibenclamide (10 μmol/L), a KATP channel inhibitor, attenuated the simvastatin‐induced de‐differentiation (0.84 ± 0.05). Direct inhibition of mitochondrial respiration by oligomycin (1 ng/mL) also produced a de‐differentiation effect (0.33 ± 0.02). OCR (pmol O2/min/μg protein) was significantly decreased in the simvastatin‐treated hVFs, including basal (P = 0.002), ATP‐linked (P = 0.01), proton leak‐linked (P = 0.01), and maximal (P < 0.001). The OCR inhibition was prevented by GGPP (basal OCR [P = 0.02], spare capacity OCR [P = 0.008], and maximal OCR [P = 0.003]). Congruently, hVFs from HF showed an increased population of myofibroblasts while HF + statin group showed significantly reduced cellular respiration (basal OCR [P = 0.021], ATP‐linked OCR [P = 0.047], maximal OCR [P = 0.02], and spare capacity OCR [P = 0.025]) and myofibroblast differentiation (α‐SMA/GAPDH: 1 ± 0.19 vs. 0.23 ± 0.06, P = 0.01).ConclusionsThis study demonstrates the de‐differentiating effect of statins, the underlying GGPP sensitivity, reduced OCR with potential activation of KATP channels, and their impact on the differentiation magnitude of hVFs in HF patients. ...

In addition to their role in many vital cellular functions, arachidonic acid (AA) and its eicosanoid metabolites are involved in the pathogenesis of several diseases, including atherosclerosis and cancer. To understand the potential mechanisms by which these lipid molecules could influence the disease processes, particularly cardiovascular diseases, we studied AA's effects on vascular smooth muscle cell (VSMC) motility and the role of cAMPresponse element binding protein-1 (CREB-1) in this process. AA exerted differential effects on VSMC motility; at lower doses, it stimulated motility, whereas at higher doses, it was inhibitory. AA-induced VSMC motility requires its conversion via the lipoxygenase (LOX) and cyclooxygenase (COX) pathways. AA stimulated the phosphorylation of extracellular signal-regulated kinases (ERKs), Jun N-terminal kinases ( JNKs), and p38 mitogen-activated protein kinase (p38MAPK) in a time-dependent manner, and blockade of these serine/threonine kinases significantly attenuated AAinduced VSMC motility. In addition, AA stimulated CREB-1 phosphorylation and activity in a manner that was also dependent on its metabolic conversion via the LOX and COX pathways and the activation of ERKs and p38MAPK but not JNKs. Furthermore, suppression of CREB-1 activation inhibited AA-induced VSMC motility. 15(S)-Hydroxyeicosatetraenoic acid and prostaglandin F 2a , the 15-LOX and COX metabolites of AA, respectively, that are produced by VSMC at lower doses, were also found to stimulate motility in these cells. Together, these results suggest that AA induces VSMC motility by complex mechanisms involving its metabolism via the LOX and COX pathways as well as the ERK-and p38MAPK-dependent and JNK-independent activation of CREB-1.-Dronadula, N., F. Rizvi, E. Blaskova, Q. Li, and G. N. Rao. Involvement of cAMP-response element binding protein-1 in arachidonic acid-induced vascular smooth muscle cell motility. J. Lipid Res. 2006. 47: 767-777.

No abstract