Elsevier

Mitochondrion

Volume 54, September 2020, Pages 8-14
Mitochondrion

Original Research Article
Altered mitochondrial proteome and functional dynamics in patients with rheumatoid arthritis

https://doi.org/10.1016/j.mito.2020.06.005Get rights and content

Highlights

Abstract

The autoimmune inflammatory disease, Rheumatoid arthritis (RA), has known imbalances in energy metabolism and superoxide levels thus may have an etiology associated with mitochondrial dysfunction. We thus evaluated the presence of a differential mitochondrial proteome as well as other characteristics including mitochondrial mass, membrane potential (Ψm), total cellular ATP and superoxide levels. Eighteen mitochondrial proteins were down-regulated while four were up-regulated in RA patients in comparison to the healthy controls (HC). A significant decrease in mitochondrial Ψm, superoxides and cellular ATP levels was observed in RA with constant mitochondrial mass suggesting mitochondrial dysfunction responsible for functional disparity in RA.

Introduction

Immune system defends our body against invaders and while doing so it needs to expend energy to fight infections (Ganeshan and Chawla, 2014). An immune dysfunction can lead to autoimmunity wherein the self-damaging immune effector responses are manifested (Janeway et al., 2001). Mitochondria are specialized organelles extensively identified for their bioenergetic capacities as well as numerous cellular functions including calcium signalling, steroid and heme synthesis, cellular metabolism and apoptosis (Chinnery and Hudson, 2013). Subtle changes in the mitochondrial capacities accounting for an imbalance between energy production and demand as well as transfer of different signalling components can lead to amplified disturbances in cellular structures and functions thereby playing important roles in various pathological conditions. Thus understanding the involvement of mitochondria in pathogenesis of different diseases becomes crucial.

Any alteration in mitochondrial oxidative phosphorylation (OXPHOS), mitochondrial membrane potential (ΔΨm), respiration, reactive oxygen species (ROS) production, proton leak, classified as mitochondrial dysfunction, can critically regulate numerous cellular signalling mechanisms (Brand and Nicholls, 2011) and has been reported in pathogenesis of various metabolic and autoimmune diseases including diabetes (Pieczenik and Neustadt, 2007), Huntington’s disease (Pieczenik and Neustadt, 2007), Systemic lupus erythematosus (SLE) (Perl et al., 2004), Sjogren’s syndrome (Pagano et al., 2013) and different cancers (Hsu et al., 2016).

Rheumatoid arthritis (RA) is a systemic and chronic inflammatory disease with autoimmune responses and inflammation leading to bone and joint destruction (Chimenti et al., 2015). Both innate and adaptive immune systems play discrete roles in contributing towards RA pathology (Chimenti et al., 2015). The bystander activation of immune cells at the joints further amplifies the disease symptoms (Chimenti et al., 2015). Mitochondria play an important role in metabolic reprogramming of immune cells to meet the altered bioenergetic demands. Recent reports suggest important links between mitochondrial respiratory and metabolic capacities with development of T cell effector and memory functions (Buck et al., 2016). Osteoclast survival and bone resorption capacities have also been directly associated with mitochondrial capacities of ATP production (Miyazaki et al., 2012). We also reported changes in cell free DNA, including mitochondrial DNA (mtDNA), in RA patients that may be involved in pathogenesis of the disease (Khanna et al., 2018). As RA is characterized by the integral changes in peripheral and migrant site specific immune cells, osteoclasts and fibroblasts, it thus becomes essential to monitor and analyze the metabolic machinery of these cells to build better therapeutic strategies directly targeting the mitochondria to improve patient’s health. We thus analyzed and quantified the differential mitochondrial proteome in RA patients using isobaric tags for relative and absolute quantitation (iTRAQ) labelling coupled with liquid chromatography-tandem mass spectrometry (LC–MS/MS) followed by mRNA transcript analysis to assess changes that might be responsible for the observed differences in the proteome. Any anomalies in mitochondrial functions were assessed in parallel in RA PBMCs.

Section snippets

Patient inclusion

Seventy-six RA patients satisfying the 2010 ACR/EULAR classification criteria for RA diagnosis (McGeough and Bjourson, 2012), visiting rheumatology outpatient department of Pradyumna Bal Memorial Hospital, Bhubaneswar, Odisha, India and eighty seven healthy controls (HC) who donated blood at blood bank of Pradyumna Bal Memorial Hospital, Bhubaneswar were enrolled in this study. The study was approved by Institute and Hospital Research Ethics committee and all the procedures were performed in

Differential mitochondrial proteome in RA PBMCs

Using iTRAQ-LC–MS/MS followed by bioinformatics analyses, a total of 198 mitochondrial proteins were identified in each technical triplicate of both the pools of RA and HC mitochondrial protein samples (Table S4). Upon setting a fold change threshold values of 0.8 for downregulation and 1.2 for upregulation of proteins and a significance level with p-value ≤ 0.05 based on the previously published references (Li et al., 2019, Sun et al., 2017, Zhou et al., 2016) for both the biological pool

Discussion

During OXPHOS, electrons transport and proton pumping results in generation of ΔΨm which is required for ATP production (Li et al., 2006). Inefficient H+ pumping reduces ΔΨm causing lower ATP production and increased heat per calorie consumed (Li, 2012). Deficiency of OXPHOS leads to attenuated mitochondrial function (Li et al., 2015) and has been reported in different diseases (Hsu et al., 2016, Kim et al., 2017). The differential proteome analysis of our case control cohort depicts a

Conclusion

Differential expressions of the above discussed proteins indicate presence of dysfunctional mitochondria in immune cells of RA patients where complex I, II, IV and OXPHOS are compromised, membrane potential, ATP generation and mitochondrial superoxide levels are diminished, fatty acid and ketone body metabolism are compromised, phagosome maturation is upregulated, proteins involved in mitochondrial transcription and translation have altered expressions, mitophagy related proteins are

Acknowledgements

The study was supported by Department of Science and Technology (DST), India (ECR/2015/000300). Shweta Khanna is thankful to Indian Council of Medical Research for Senior Research Fellowship (Ref. No. 3/1/2/(4)/CD/18NCD-II).

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