Low-grade Chronic Inflammation: A Shared Mechanism for Chronic Diseases.

Inflammation is an important physiological response of the organism to restore homeostasis upon pathogenic or damaging stimuli. However, persistence of the harmful trigger, or a deficient resolution of the process can evolve into a state of low-grade, chronic inflammation. This condition is strongly associated to the development of several increasingly prevalent and serious chronic conditions such as obesity, cancer and cardiovascular diseases, elevating overall morbidity and mortality worldwide. The current pandemic of chronic diseases underscores the need to address chronic inflammation, its pathogenic mechanisms and potential preventive measures to limit its current widespread impact. The present review discusses the current knowledge and research gaps regarding the association between low-grade chronic inflammation and chronic diseases, focusing on obesity, cardiovascular diseases, digestive diseases and cancer. We examine the state-of-the-art in selected aspects of the topic, and propose future directions and approaches for the field.

Early left atrial dysfunction is associated with suboptimal cardiovascular health.

AIMS: Two-dimensional speckle-tracking echocardiography can assess left atrial (LA) function by measuring atrial volumes and deformation parameters (strain, strain rate). This cross-sectional analysis explores the association between ideal CV health (CVH), LA function, and systemic biomarkers in healthy individuals from the Chilean MAUCO Cohort. METHODS: We enrolled 95 MAUCO participants with different levels of CVH (mean age: 51 ± 8 years). We categorized participants into low or high CVH groups: A: 0-2, or B: 3-6 CVH risk factors. 2D echocardiography, glucose, insulin, total cholesterol, triglycerides, proBNP, hsCRP, insulin resistance index (HOMA), and right and left atrial strain (RASs and LASs, respectively) were determined. RESULTS: LASs was lower in Group A, while systolic and diastolic blood pressure (BP), body mass index (BMI), insulin, HOMA, total cholesterol, triglycerides, and LV and RV end-diastolic volume were significantly higher in Group A than Group B (P < .01). Change in LASs was inversely correlated with insulin (P = .040), HOMA (P = .013), total cholesterol (P = .039), glycemia (P = .018), and BMI (P = .0.037). CONCLUSION: LASs during the reservoir phase was diminished in subjects with a lower level of CVH. Higher insulin, HOMA, total cholesterol, glycemia, and BMI values were associated with decreased LA deformation during the reservoir phase. Morphofunctional alterations of the LA were also identified in the group with suboptimal CVH, as well as BP values in the range of hypertension. LA dysfunction in an asymptomatic population, along with metabolic syndrome, could be an early event in the continuum of CV damage.

Increased active phase atrial contraction is related to marathon runner performance.

PURPOSE: Left atrial (LA) contraction is essential for left ventricular (LV) filling during exertion. We sought to evaluate the relationship of LA contraction and exercise capacity in trained athletes. METHODS: Sixteen male marathon runners were recruited and allocated into two groups according to their previous training status (≥ or < 100 km peer week). All subjects underwent a baseline cardiopulmonary test to evaluate maximal aerobic capacity and a transthoracic echocardiography previous and immediate post-marathon. LA contractile function evaluation was accomplished by measuring the negative deformation of the post P wave strain curve (LASa). LASa change was defined as LASa pre-marathon minus LASa immediate post-marathon. RESULTS: Mean age was 39 ± 6 years. LA volume index (39 ± 13 vs. 31 ± 5 mL/m2, p = 0.04), LV mass index (91 ± 21 vs. 73 ± 12 g/m2, p = 0.04), VO2 max (59 ± 3 vs. 50 ± 8 mL/kg/min, p = 0.036) were higher in more intensive trained group and marathon time was lower (185 ± 14 vs. 219 ± 24 min, p = 0.017). An increase in LASa after immediate post-marathon was observed in both groups, which was significantly greater in the highly trained group (18.9 ± 5.8 vs. 6.3 ± 3.5%, p < 0.003). Maximum VO2 measured previous to the marathon was inversely related to marathon time and directly correlated to LASa change (rho = 0.744, p = 0.001, rho = 0.546, p = 0.028, respectively). CONCLUSIONS: Athletes with more intensive training load have larger LV mass and LA size. An increase in LA contraction was seen post-marathon, which was significantly greater in the highly trained group. This increase in the LA contraction was related to the maximum VO2 measured previous to the marathon and to performance in a highly demanding test.

[Cardiotoxicity of anticancer therapies. Towards the implementation of cardio-oncology units]. / Cardiotoxicidad inducida por tratamientos oncológicos. Fundamentos para la implementación de equipos de Cardio-Oncología.

Recently, we have witnessed major improvements in cancer treatment. Early diagnosis and development of new therapies have reduced cancer-related mortality. However, these new therapies, along with greater patient survival, are associated with an increase in untoward effects, particularly in the cardiovascular system. Although cardiotoxicity induced by oncologic treatments affects predominantly the myocardium, it can also involve other structures of the cardiovascular system, becoming one of the main causes of morbidity and mortality in those who survive cancer. The main objective of cardio-oncology is to achieve the maximum benefits of oncologic treatments while minimizing their deleterious cardiovascular effects. It harbors the stratification of patients at risk of cardiotoxicity, the implementation of diagnostic tools (imaging techniques and biomarkers) for early diagnosis, preventive strategies and early treatment options for the complications. Herein, we discuss the basic knowledge for the implementation of cardio-oncology units and their role in the management of cancer patients, the diagnostic tools available to detect cardiotoxicity and the present therapeutic options.

Inhibition of mitochondrial fission prevents hypoxia-induced metabolic shift and cellular proliferation of pulmonary arterial smooth muscle cells.

Chronic hypoxia exacerbates proliferation of pulmonary arterial smooth muscle cells (PASMC), thereby reducing the lumen of pulmonary arteries. This leads to poor blood oxygenation and cardiac work overload, which are the basis of diseases such as pulmonary artery hypertension (PAH). Recent studies revealed an emerging role of mitochondria in PAH pathogenesis, as key regulators of cell survival and metabolism. In this work, we assessed whether hypoxia-induced mitochondrial fragmentation contributes to the alterations of both PASMC death and proliferation. In previous work in cardiac myocytes, we showed that trimetazidine (TMZ), a partial inhibitor of lipid oxidation, stimulates mitochondrial fusion and preserves mitochondrial function. Thus, here we evaluated whether TMZ-induced mitochondrial fusion can prevent human PASMC proliferation in an in vitro hypoxic model. Using confocal fluorescence microscopy, we showed that prolonged hypoxia (48h) induces mitochondrial fragmentation along with higher levels of the mitochondrial fission protein DRP1. Concomitantly, both mitochondrial potential and respiratory rates decreased, indicative of mitochondrial dysfunction. In accordance with a metabolic shift towards non-mitochondrial ATP generation, mRNA levels of glycolytic markers HK2, PFKFB2 and GLUT1 increased during hypoxia. Incubation of PASMC with TMZ, prior to hypoxia, prevented all these changes and precluded the increase in PASMC proliferation. These findings were also observed using Mdivi-1 (a pharmacological DRP1 inhibitor) or a dominant negative DRP1 K38A as pre-treatments. Altogether, our data indicate that TMZ exerts a protective role against hypoxia-induced PASMC proliferation, by preserving mitochondrial function, thus highlighting DRP1-dependent morphology as a novel therapeutic approach for diseases such as PAH.

Acute effect of iloprost inhalation on right atrial function and ventricular dyssynchrony in patients with pulmonary artery hypertension.

BACKGROUND: Right atrium function and ventricular function have significant prognostic value in pulmonary arterial hypertension patients. Acute changes in right ventricular synchrony and right atrium function postiloprost inhalation have not been evaluated. METHODS: Cross-sectional study. Consecutive pulmonary arterial hypertension patients (group I from Nice classification) were included. Echocardiographic right atrium and right ventricular function pre- and postiloprost inhalation, including a right ventricular dyssynchrony index and right atrium function using speckle tracking, were performed in all patients. RESULTS: Twenty pulmonary arterial hypertension patients, 44±7 years and 90% females, were included. After iloprost inhalation, we observed a significant increment in right ventricular fractional area change and a significant decrease in right ventricular dyssynchrony index (21.4±5.6% vs 26.1±4.0 %, P=.007 and 79±44 vs 32±22 mseconds, P<.01, respectively), also an improvement in right atrium reservoir function (8.6±3.1% vs 11.7±3.5 %, P=.002). CONCLUSIONS: Iloprost inhalation induces acute changes in right ventricular function, dyssynchrony, and right atrium performance that may add relevant clinical information in the management and risk stratification of pulmonary arterial hypertension patients.

ER-to-mitochondria miscommunication and metabolic diseases.

Eukaryotic cells contain a variety of subcellular organelles, each of which performs unique tasks. Thus follows that in order to coordinate these different intracellular functions, a highly dynamic system of communication must exist between the various compartments. Direct endoplasmic reticulum (ER)-mitochondria communication is facilitated by the physical interaction of their membranes in dedicated structural domains known as mitochondria-associated membranes (MAMs), which facilitate calcium (Ca(2+)) and lipid transfer between organelles and also act as platforms for signaling. Numerous studies have demonstrated the importance of MAM in ensuring correct function of both organelles, and recently MAMs have been implicated in the genesis of various human diseases. Here, we review the salient structural features of interorganellar communication via MAM and discuss the most common experimental techniques employed to assess functionality of these domains. Finally, we will highlight the contribution of MAM to a variety of cellular functions and consider the potential role of MAM in the genesis of metabolic diseases. In doing so, the importance for cell functions of maintaining appropriate communication between ER and mitochondria will be emphasized.

Defective insulin signaling and mitochondrial dynamics in diabetic cardiomyopathy.

Diabetic cardiomyopathy (DCM) is a common consequence of longstanding type 2 diabetes mellitus (T2DM) and encompasses structural, morphological, functional, and metabolic abnormalities in the heart. Myocardial energy metabolism depends on mitochondria, which must generate sufficient ATP to meet the high energy demands of the myocardium. Dysfunctional mitochondria are involved in the pathophysiology of diabetic heart disease. A large body of evidence implicates myocardial insulin resistance in the pathogenesis of DCM. Recent studies show that insulin signaling influences myocardial energy metabolism by impacting cardiomyocyte mitochondrial dynamics and function under physiological conditions. However, comprehensive understanding of molecular mechanisms linking insulin signaling and changes in the architecture of the mitochondrial network in diabetic cardiomyopathy is lacking. This review summarizes our current understanding of how defective insulin signaling impacts cardiac function in diabetic cardiomyopathy and discusses the potential role of mitochondrial dynamics.

Study protocol for the Maule Cohort (MAUCO) of chronic diseases, Chile 2014-2024.

BACKGROUND: Maule Cohort (MAUCO), a Chilean cohort study, seeks to analyze the natural history of chronic diseases in the agricultural county of Molina (40,000 inhabitants) in the Maule Region, Chile. Molina´s population is of particular interest because in the last few decades it changed from being undernourished to suffering excess caloric intake, and it currently has the highest national rates of cardiovascular diseases, stomach cancer and gallbladder cancer. Between 2009 and 2011 Molina´s poverty rate dropped from 24.1 % to 13.5 % (national average 20.4 %); in this period the county went from insufficient to almost complete basic sanitation. Despite these advances, chemical pollutants in the food and air are increasing. Thus, in Molina risk factors typical of both under-developed and developed countries coexist, generating a unique profile associated with inflammation, oxidative stress and chronic diseases. METHODS/DESIGN: MAUCO is the core project of the recently established Advanced Center for Chronic Diseases (ACCDiS), Universidad de Chile & Pontificia Universidad Católica de Chile. In this study, we are enrolling and following 10,000 adults aged 38 to 74 years over 10 years. All eligible Molina residents will be enrolled. Participants were identified through a household census. Consenting individuals answer an epidemiological survey exploring risk factors (psycho-social, pesticides, diet, alcohol, and physical activity), medical history and physical and cognitive conditions; provide fasting blood, urine, and saliva samples; receive an electrocardiogram, abdominal ultrasound and bio-impedance test; and take a hand-grip strength test. These subjects will be re-interviewed after 2, 5 and 7 years. Active surveillance of health events is in place throughout the regional healthcare system. The MAUCO Bio-Bank will store 30 to 50 aliquots per subject using an NIH/NCI biorepository system for secure and anonymous linkage of samples with data. DISCUSSION: MAUCO´s results will help design public health interventions tailored to agricultural populations in Latin America.

Atrial Function Assessed by Speckle Tracking Echocardiography Is a Good Predictor of Postoperative Atrial Fibrillation in Elderly Patients.

OBJECTIVE: Advanced age is an independent predictor of postoperative atrial fibrillation (POAF) in patients undergoing coronary artery bypass surgery. We evaluated whether left atrial (LA) dysfunction assessed by strain contributes to identifying elderly patients prone to POAF. METHODS: Case-control study of 70 subjects undergoing coronary artery bypass surgery. Clinical and laboratory characteristics were recorded at baseline and 72 hours after surgery. Echocardiography was performed during the preoperative period; LA dimensions and deformation by strain (systolic wave [LASs]) as well as strain rate (systolic wave [LASRs] and atrial contraction wave [LASRa]) were assessed. RESULTS: Postoperative atrial fibrillation occurred in 38.5% of patients within the first 72 hours after surgery (28.5% of the younger vs. 48.6% of the older group). Baseline and postoperative inflammatory markers as well as total surgical and aortic clamp time were similar between groups. LA function was markedly impaired in subjects with POAF. Age correlated with LASs, LASRs, and LASRa. These associations remained consistent when subjects 75 years or older were considered separately. Both LASs and LASRa for patients with or without POAF, respectively, were significantly impaired in elderly subjects with POAF. Multivariate analysis provided further evidence that both LASs and age are independent predictors for POAF. CONCLUSION: Age-related changes in atrial function preceding atrial dilation are evident only upon LA strain analysis. LA strain impairment is an independent predictor of POAF irrespective of age and may serve as a surrogate marker for biological processes involved in establishing the substrate for POAF.

Socioeconomic Inequalities in Heart Failure.

Prevalence and incidence of chronic heart failure (CHF) has increased during the past decades. Beyond its impact on mortality rates, CHF severely impairs quality of life, particularly with the elderly and vulnerable population. Several studies have shown that CHF takes its toll mostly on the uneducated, low-income population, who exhibit impaired access to health care systems, less knowledge regarding its pathology and poorer self-care behaviors. This review summarizes the available evidence linking socioeconomic inequalities and CHF, focusing on the modifiable factors that may explain the impaired health outcomes in socioeconomically deprived populations.

Heart Failure in Rural Communities.

Patients with chronic heart failure (CHF) living in rural areas face an increased risk of adverse cardiovascular events. Even in countries with universal access to health care, rural areas are characteristically underserved, with reduced health care providers supply, greater distance to health care centers, decreased physician density with higher reliance on generalists, and high health care staff turnover. On the other hand, patient-related characteristics vary widely among published data. This review describes the epidemiology of CHF in rural or remote settings, organizational and patient-related factors involved in cardiovascular outcomes, and the role of interventions to improve rural health care.

Effects of trimetazidine in nonischemic heart failure: a randomized study.

OBJECTIVES: Heart failure (HF) is associated with changes in myocardial metabolism that lead to impairment of contractile function. Trimetazidine (TMZ) modulates cardiac energetic efficiency and improves outcomes in ischemic heart disease. We evaluated the effects of TMZ on left ventricular ejection fraction (LVEF), cardiac metabolism, exercise capacity, O2 uptake, and quality of life in patients with nonischemic HF. METHODS AND RESULTS: Sixty patients with stable nonischemic HF under optimal medical therapy were included in this randomized double-blind study. Patients were randomized to TMZ (35 mg orally twice a day) or placebo for 6 months. LVEF, 6-minute walk test (6MWT), maximum O2 uptake in cardiopulmonary exercise test, different markers of metabolism, oxidative stress, and endothelial function, and quality of life were assessed at baseline and after TMZ treatment. Left ventricular peak glucose uptake was evaluated with the use of the maximum standardized uptake value (SUV) by 18-fluorodeoxyglucose positron emission tomography ((18)FDG-PET). Etiology was idiopathic in 85% and hypertensive in 15%. Both groups were similar in age, functional class, LVEF, and levels of N-terminal pro-B-type natriuretic peptide at baseline. After 6 months of TMZ treatment, no changes were observed in LVEF (31 ± 10% vs 34 ± 8%; P = .8), 6MWT (443 ± 25 m vs 506 ± 79 m; P = .03), maximum O2 uptake (19.1 ± 5.0 mL kg(-1) min(-1) vs 23.0 ± 7.2 mL kg(-1) min(-1); P = .11), functional class (percentages of patients in functional classes I/II/III/IV 10/3753/0 vs 7/40/50/3; P = .14), or quality of life (32 ± 26 points vs 24 ± 18 points; P = .25) in TMZ versus placebo, respectively. In the subgroup of patients evaluated with (18)FDG-PET, no significant differences were observed in SUV between both groups (7.0 ± 3.6 vs 8.2 ± 3.4 respectively; P = .47). CONCLUSIONS: In patients with nonischemic HF, the addition of TMZ to optimal medical treatment does not result in significant changes of LVEF, exercise capacity, O2 uptake, or quality of life.

Effects of Trimetazidine on Right Ventricular Function and Ventricular Remodeling in Patients with Pulmonary Artery Hypertension: A Randomised Controlled Trial.

BACKGROUND: Pulmonary artery hypertension (PAH) is a chronic and progressive disease. Although current therapy has improved the disease prognosis, PAH has a poor survival rate. The key feature leading to disease progression and death is right ventricular (RV) failure. METHODS AND RESULTS: We assessed the role of trimetazidine, a fatty acid beta-oxidation (FAO) inhibitor, in right ventricular function, remodeling, and functional class in PAH patients, with a placebo-controlled double-blind, case-crossover trial. Twenty-seven PAH subjects were enrolled, randomized, and assigned to trimetazidine or placebo for three months and then reallocated to the other study arm. The primary endpoint was RV morphology and function change after three months of treatment. Secondary endpoints were the change in exercise capacity assessed by a 6 min walk test after three months of treatment and the change in pro-BNP and Galectin-3 plasma levels after three months. Trimetazidine use was safe and well-tolerated. After three months of treatment, patients in the trimetazidine group showed a small but significant reduction of RV diastolic area, and a substantial increase in the 6 min walk distance (418 vs. 438 mt, p = 0.023), without significant changes in biomarkers. CONCLUSIONS: A short course of trimetazidine is safe and well-tolerated on PAH patients, and it is associated with significant increases in the 6MWT and minor but significant improvement in RV remodeling. The therapeutic potential of this drug should be evaluated in larger clinical trials.

Targeting VCAM-1: a therapeutic opportunity for vascular damage.

INTRODUCTION: The vascular cell adhesion molecule (VCAM-1) is a transmembrane sialoglycoprotein detected in activated endothelial and vascular smooth muscle cells involved in the adhesion and transmigration of inflammatory cells into damaged tissue. Widely used as a pro-inflammatory marker, its potential role as a targeting molecule has not been thoroughly explored. AREAS COVERED: We discuss the current evidence supporting the potential targeting of VCAM-1 in atherosclerosis, diabetes, hypertension and ischemia/reperfusion injury. EXPERT OPINION: There is emerging evidence that VCAM-1 is more than a biomarker and may be a promising therapeutic target for vascular diseases. While there are neutralizing antibodies that allow preclinical research, the development of pharmacological tools to activate or inhibit this protein are required to thoroughly assess its therapeutic potential.

Mitochondria, myocardial remodeling, and cardiovascular disease.

The process of muscle remodeling lies at the core of most cardiovascular diseases. Cardiac adaptation to pressure or volume overload is associated with a complex molecular change in cardiomyocytes which leads to anatomic remodeling of the heart muscle. Although adaptive at its beginnings, the sustained cardiac hypertrophic remodeling almost unavoidably ends in progressive muscle dysfunction, heart failure and ultimately death. One of the features of cardiac remodeling is a progressive impairment in mitochondrial function. The heart has the highest oxygen uptake in the human body and accordingly it has a large number of mitochondria, which form a complex network under constant remodeling in order to sustain the high metabolic rate of cardiac cells and serve as Ca(2+) buffers acting together with the endoplasmic reticulum (ER). However, this high dependence on mitochondrial metabolism has its costs: when oxygen supply is threatened, high leak of electrons from the electron transport chain leads to oxidative stress and mitochondrial failure. These three aspects of mitochondrial function (Reactive oxygen species signaling, Ca(2+) handling and mitochondrial dynamics) are critical for normal muscle homeostasis. In this article, we will review the latest evidence linking mitochondrial morphology and function with the process of myocardial remodeling and cardiovascular disease.

A potential role of autophagy-mediated vascular senescence in the pathophysiology of HFpEF.

Heart failure with preserved ejection fraction (HFpEF) is one of the most complex and most prevalent cardiometabolic diseases in aging population. Age, obesity, diabetes, and hypertension are the main comorbidities of HFpEF. Microvascular dysfunction and vascular remodeling play a major role in its development. Among the many mechanisms involved in this process, vascular stiffening has been described as one the most prevalent during HFpEF, leading to ventricular-vascular uncoupling and mismatches in aged HFpEF patients. Aged blood vessels display an increased number of senescent endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). This is consistent with the fact that EC and cardiomyocyte cell senescence has been reported during HFpEF. Autophagy plays a major role in VSMCs physiology, regulating phenotypic switch between contractile and synthetic phenotypes. It has also been described that autophagy can regulate arterial stiffening and EC and VSMC senescence. Many studies now support the notion that targeting autophagy would help with the treatment of many cardiovascular and metabolic diseases. In this review, we discuss the mechanisms involved in autophagy-mediated vascular senescence and whether this could be a driver in the development and progression of HFpEF.

Systemic oxidative stress and endothelial dysfunction is associated with an attenuated acute vascular response to inhaled prostanoid in pulmonary artery hypertension patients.

BACKGROUND: Systemic endothelial dysfunction and increased oxidative stress have been observed in pulmonary arterial hypertension (PAH). We evaluate whether oxidative stress and endothelial dysfunction are associated with acute pulmonary vascular bed response to an inhaled prostanoid in PAH patients. METHODS: Fourteen idiopathic PAH patients and 14 controls were included. Oxidative stress was assessed through plasma malondialdehyde (MDA) levels and xanthine oxidase (XO) and endothelial-bound superoxide dismutase (eSOD) activity. Brachial artery endothelial-dependent flow-mediated vasodilation (FMD) was used to evaluate endothelial function. Hemodynamic response to inhaled iloprost was assessed with transthoracic echocardiography. RESULTS: PAH patients showed impaired FMD (2.8 ± 0.6 vs. 10.7 ± 0.6%, P < .01), increased MDA levels and XO activity (0.6 ± 0.2 vs. 0.3 ± 0.2 µM, P < .01 and 0.04 ± 0.01 vs. 0.03 ± 0.01 U/mL, P = .02, respectively) and decreased eSOD activity (235 ± 23 vs. 461 ± 33 AUC, P < .01). Iloprost improved right cardiac output (3.7 ± 0.6 to 4.1 ± 1.2 L/min, P = .02) and decreased pulmonary vascular resistance (4.1 ± 1.1 to 2.9 ± 0.9 Wood U, P = .01). Changes in right cardiac output after prostanoid inhalation correlated significantly with baseline eSOD activity and FMD (Rho: 0.61, P < .01 and Rho: 0.63, P = .01, respectively). CONCLUSION: PAH patients show increased systemic oxidative stress and endothelial dysfunction markers. Response to inhaled prostanoid is inversely related to both parameters.

Mitochondrial function, dynamics and quality control in the pathophysiology of HFpEF.

Heart failure (HF) is one of the leading causes of hospitalization for the adult population and a major cause of mortality worldwide. The HF syndrome is characterized by the heart's inability to supply the cardiac output required to meet the body's metabolic requirements or only at the expense of elevated filling pressures. HF without overt impairment of left ventricular ejection fraction (LVEF) was initially labeled as "diastolic HF" until recognizing the coexistence of both systolic and diastolic abnormalities in most cases. Acknowledging these findings, the preferred nomenclature is HF with preserved EF (HFpEF). This syndrome primarily affects the elderly population and is associated with a heterogeneous overlapping of comorbidities that makes its diagnosis challenging. Despite extensive research, there is still no evidence-based therapy for HFpEF, reinforcing the need for a thorough understanding of the pathophysiology underlying its onset and progression. The role of mitochondrial dysfunction in developing the pathophysiological changes that accompany HFpEF onset and progression (low-grade systemic inflammation, oxidative stress, endothelial dysfunction, and myocardial remodeling) has just begun to be acknowledged. This review summarizes our current understanding of the participation of the mitochondrial network in the pathogenesis of HFpEF, with particular emphasis on the signaling pathways involved, which may provide future therapeutic targets.

Endoplasmic reticulum-mitochondria coupling increases during doxycycline-induced mitochondrial stress in HeLa cells.

Subcellular organelles communicate with each other to regulate function and coordinate responses to changing cellular conditions. The physical-functional coupling of the endoplasmic reticulum (ER) with mitochondria allows for the direct transfer of Ca2+ between organelles and is an important avenue for rapidly increasing mitochondrial metabolic activity. As such, increasing ER-mitochondrial coupling can boost the generation of ATP that is needed to restore homeostasis in the face of cellular stress. The mitochondrial unfolded protein response (mtUPR) is activated by the accumulation of unfolded proteins in mitochondria. Retrograde signaling from mitochondria to the nucleus promotes mtUPR transcriptional responses aimed at restoring protein homeostasis. It is currently unknown whether the changes in mitochondrial-ER coupling also play a role during mtUPR stress. We hypothesized that mitochondrial stress favors an expansion of functional contacts between mitochondria and ER, thereby increasing mitochondrial metabolism as part of a protective response. Hela cells were treated with doxycycline, an antibiotic that inhibits the translation of mitochondrial-encoded proteins to create protein disequilibrium. Treatment with doxycycline decreased the abundance of mitochondrial encoded proteins while increasing expression of CHOP, C/EBPß, ClpP, and mtHsp60, markers of the mtUPR. There was no change in either mitophagic activity or cell viability. Furthermore, ER UPR was not activated, suggesting focused activation of the mtUPR. Within 2 h of doxycycline treatment, there was a significant increase in physical contacts between mitochondria and ER that was distributed throughout the cell, along with an increase in the kinetics of mitochondrial Ca2+ uptake. This was followed by the rise in the rate of oxygen consumption at 4 h, indicating a boost in mitochondrial metabolic activity. In conclusion, an early phase of the response to doxycycline-induced mitochondrial stress is an increase in mitochondrial-ER coupling that potentiates mitochondrial metabolic activity as a means to support subsequent steps in the mtUPR pathway and sustain cellular adaptation.