Tafazzin deficiency impairs mitochondrial metabolism and function of lipopolysaccharide activated B lymphocytes in mice

Human mesenchymal stem cells exhibit altered mitochondrial dynamics and poor survival in high glucose microenvironment

BACKGROUND

Mesenchymal stem cells (MSCs) are a type of stem cells that possess relevant regenerative abilities and can be used to treat many chronic diseases. Diabetes mellitus (DM) is a frequently diagnosed chronic disease characterized by hyperglycemia which initiates many multisystem complications in the long-run. DM patients can benefit from MSCs transplantation to curb down the pathological consequences associated with hyperglycemia persistence and restore the function of damaged tissues. MSCs therapeutic outcomes are found to last for short period of time and ultimately these regenerative cells are eradicated and died in DM disease model.

AIM

To investigate the impact of high glucose or hyperglycemia on the cellular and molecular characteristics of MSCs.

METHODS

Human adipose tissue-derived MSCs (hAD-MSCs) were seeded in low (5.6 mmol/L of glucose) and high glucose (25 mmol/L of glucose) for 7 d. Cytotoxicity, viability, mitochondrial dynamics, and apoptosis were deplored using specific kits. Western blotting was performed to measure the protein expression of phosphatidylinositol 3-kinase (PI3K), TSC1, and mammalian target of rapamycin (mTOR) in these cells.

RESULTS

hAD-MSCs cultured in high glucose for 7 d demonstrated marked decrease in their viability, as shown by a significant increase in lactate dehydrogenase (P < 0.01) and a significant decrease in Trypan blue (P < 0.05) in these cells compared to low glucose control. Mitochondrial membrane potential, indicated by tetramethylrhodamine ethyl ester (TMRE) fluorescence intensity, and nicotinamide adenine dinucleotide (NAD+)/NADH ratio were significantly dropped (P < 0.05 for TMRE and P < 0.01 for NAD+/NADH) in high glucose exposed hAD-MSCs, indicating disturbed mitochondrial function. PI3K protein expression significantly decreased in high glucose culture MSCs (P < 0.05 compared to low glucose) and it was coupled with significant upregulation in TSC1 (P < 0.05) and downregulation in mTOR protein expression (P < 0.05). Mitochondrial complexes I, IV, and V were downregulated profoundly in high glucose (P < 0.05 compared to low glucose). Apoptosis was induced as a result of mitochondrial impairment and explained the poor survival of MSCs in high glucose.

CONCLUSION

High glucose impaired the mitochondrial dynamics and regulatory proteins in hAD-MSCs ensuing their poor survival and high apoptosis rate in hyperglycemic microenvironment.

Reduction in mRNA Expression of the Neutrophil Chemoattract Factor CXCL1 in Pseudomonas aeruginosa Treated Barth Syndrome B Lymphoblasts

Barth Syndrome (BTHS) is a rare X-linked genetic disease caused by a mutation in the TAFAZZIN gene, which codes for the protein tafazzin involved in cardiolipin remodeling. Approximately 70% of patients with BTHS exhibit severe infections due to neutropenia. However, neutrophils from BTHS patients have been shown to exhibit normal phagocytosis and killing activity. B lymphocytes play a crucial role in the regulation of the immune system and, when activated, secrete cytokines known to attract neutrophils to sites of infection. We examined the expression of chemokine (C-X-C motif) ligand 1 (CXCL1), a known chemotactic for neutrophils, in Epstein-Barr virus transformed control and BTHS B lymphoblasts. Age-matched control and BTHS B lymphoblasts were incubated with Pseudomonas aeruginosa for 24 h and then cell viability, CD27+, CD24+, CD38+, CD138+ and PD1+ surface marker expression and CXCL1 mRNA expression determined. Cell viability was maintained in lymphoblasts incubated in a ratio of 50:1 bacteria:B cells. Surface marker expression was unaltered between control and BTHS B lymphoblasts. In contrast, CXCL1 mRNA expression was reduced approximately 70% (p < 0.05) in untreated BTHS B lymphoblasts compared to control and approximately 90% (p < 0.05) in bacterial treated BTHS B lymphoblasts compared to the control. Thus, naïve and bacterial-activated BTHS B lymphoblasts exhibit reduced mRNA expression of the neutrophil chemoattractant factor CXCL1. We suggest that impaired bacterial activation of B cells in some BTHS patients could influence neutrophil function via impairing neutrophil recruitment to sites of infection and this could potentially contribute to these infections.

Redefining Autoimmune Disorders' Pathoetiology: Implications for Mood and Psychotic Disorders' Association with Neurodegenerative and Classical Autoimmune Disorders

Although previously restricted to a limited number of medical conditions, there is a growing appreciation that 'autoimmune' (or immune-mediated) processes are important aspects of a wide array of diverse medical conditions, including cancers, neurodegenerative diseases and psychiatric disorders. All of these classes of medical conditions are associated with alterations in mitochondrial function across an array of diverse cell types. Accumulating data indicate the presence of the mitochondrial melatonergic pathway in possibly all body cells, with important consequences for pathways crucial in driving CD8⁺ T cell and B-cell 'autoimmune'-linked processes. Melatonin suppression coupled with the upregulation of oxidative stress suppress PTEN-induced kinase 1 (PINK1)/parkin-driven mitophagy, raising the levels of the major histocompatibility complex (MHC)-1, which underpins the chemoattraction of CD8⁺ T cells and the activation of antibody-producing B-cells. Many factors and processes closely associated with autoimmunity, including gut microbiome/permeability, circadian rhythms, aging, the aryl hydrocarbon receptor, brain-derived neurotrophic factor (BDNF) and its receptor tyrosine receptor kinase B (TrkB) all interact with the mitochondrial melatonergic pathway. A number of future research directions and novel treatment implications are indicated for this wide collection of poorly conceptualized and treated medical presentations. It is proposed that the etiology of many 'autoimmune'/'immune-mediated' disorders should be conceptualized as significantly determined by mitochondrial dysregulation, with alterations in the mitochondrial melatonergic pathway being an important aspect of these pathoetiologies.

Metabolic alterations of the immune system in the pathogenesis of autoimmune diseases

Systemic autoimmune diseases are characteristically associated with aberrant autoreactive innate and adaptive immune responses that lead to tissue damage and increased morbidity and mortality. Autoimmunity has been linked to alterations in the metabolic functions of immune cells (immunometabolism) and, more specifically, to mitochondrial dysfunction. Much has been written about immunometabolism in autoimmunity in general, so this Essay focuses on recent research into the role of mitochondrial dysfunction in the dysregulation of innate and adaptive immunity that is characteristic of systemic autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Enhancing the understanding of mitochondrial dysregulation in autoimmunity will hopefully contribute to accelerating the development of immunomodulatory treatments for these challenging diseases.

Phenotypic Characterization of Male Tafazzin-Knockout Mice at 3, 6, and 12 Months of Age

Barth syndrome (BTHS) is an X-linked mitochondrial disease caused by mutations in the gene encoding for tafazzin (TAZ), a key enzyme in the remodeling of cardiolipin. Mice with a germline deficiency in Taz have been generated (Taz-KO) but not yet fully characterized. We performed physiological assessments of 3-, 6-, and 12-month-old male Taz-KO mice, including measures of perinatal survival, growth, lifespan, gross anatomy, whole-body energy and substrate metabolism, glucose homeostasis, and exercise capacity. Taz-KO mice displayed reduced viability, with lower-than-expected numbers of mice recorded at 4 weeks of age, and a shortened lifespan due to disease progression. At all ages, Taz-KO mice had lower body weights compared with wild-type (Wt) littermates despite similar absolute food intakes. This finding was attributed to reduced adiposity and diminutive organs and tissues, including heart and skeletal muscles. Although there were no differences in basal levels of locomotion between age-matched genotypes, indirect calorimetry studies showed higher energy expenditure measures and respiratory exchange ratios in Taz-KO mice. At the youngest age, Taz-KO mice had comparable glucose tolerance and insulin action to Wt mice, but while these measures indicated metabolic impairments in Wt mice with advancing age that were likely associated with increasing adiposity, Taz-KO mice were protected. Comparisons across the three age-cohorts revealed a significant and more severe deterioration of exercise capacity in Taz-KO mice than in their Wt littermate controls. The Taz-KO mouse model faithfully recapitulates important aspects of BTHS, and thus provides an important new tool to investigate pathophysiological mechanisms and potential therapies.

Tafazzin deficiency attenuates anti-cluster of differentiation 40 and interleukin-4 activation of mouse B lymphocytes

Barth syndrome (BTHS) is a rare X-linked genetic disease caused by mutations in TAFAZZIN. The tafazzin (Taz) protein is a cardiolipin remodeling enzyme required for maintaining mitochondrial function. Patients with BTHS exhibit impaired mitochondrial respiratory chain and metabolic function and are susceptible to serious infections. B lymphocytes (B cells) play a vital role in humoral immunity required to eradicate circulating antigens from pathogens. Intact mitochondrial respiration is required for proper B-cell function. We investigated whether Taz deficiency in mouse B cells altered their response to activation by anti-cluster of differentiation 40 (anti-CD40) + interleukin-4 (IL-4). B cells were isolated from 3-4-month-old wild type (WT) or tafazzin knockdown (TazKD) mice and were stimulated with anti-CD40 + IL-4 for 24 h and cellular bioenergetics, surface marker expression, proliferation, antibody production, and proteasome and immunoproteasome activities determined. TazKD B cells exhibited reduced mRNA expression of Taz, lowered levels of cardiolipin, and impairment in both oxidative phosphorylation and glycolysis compared to WT B cells. In addition, anti-CD40 + IL-4 stimulated TazKD B cells expressed lower levels of the immunogenic surface markers, cluster of differentiation 86 (CD86) and cluster of differentiation 69 (CD69), exhibited a lower proliferation rate, reduced production of immunoglobulin M and immunoglobulin G, and reduced proteasome and immunoproteasome proteolytic activities compared to WT B cells stimulated with anti-CD40 + IL-4. The results indicate that Taz is required to support T-cell-dependent signaling activation of mouse B cells.

Cardiolipin Regulates Mitochondrial Ultrastructure and Function in Mammalian Cells

Cardiolipin (CL) is a unique, tetra-acylated diphosphatidylglycerol lipid that mainly localizes in the inner mitochondria membrane (IMM) in mammalian cells and plays a central role in regulating mitochondrial architecture and functioning. A deficiency of CL biosynthesis and remodeling perturbs mitochondrial functioning and ultrastructure. Clinical and experimental studies on human patients and animal models have also provided compelling evidence that an abnormal CL content, acyl chain composition, localization, and level of oxidation may be directly linked to multiple diseases, including cardiomyopathy, neuronal dysfunction, immune cell defects, and metabolic disorders. The central role of CL in regulating the pathogenesis and progression of these diseases has attracted increasing attention in recent years. In this review, we focus on the advances in our understanding of the physiological roles of CL biosynthesis and remodeling from human patients and mouse models, and we provide an overview of the potential mechanism by which CL regulates the mitochondrial architecture and functioning.

Impaired surface marker expression in stimulated Epstein-Barr virus transformed lymphoblasts from Barth Syndrome patients

Primary B lymphocytes rapidly respond to lipopolysaccharide (LPS) and cytosine linked to a guanine by a phosphate bond deoxyribonucleic acid (CpG DNA) stimulation to promote adaptive immune function through increased surface marker expression. Here we examined expression of surface markers in LPS and CpG DNA stimulated Epstein-Barr virus transformed B lymphoblasts from control and BTHS patients with different mutations. The percentage of cluster of differentiation (CD) positive cells including CD38 + , CD138 + , CD80 + surface expression and programmed cell death protein 1 (PD1 +) surface expression was similar between control and BTHS lymphoblasts incubated plus or minus LPS. The percentage of CD24 + , CD38 + and CD138 + cells was similar between control and BTHS lymphoblasts incubated plus or minus CpG DNA. CD27 + surface marker expression was reduced in both BTHS lymphoblasts and controls incubated with CpG DNA and PD1 + surface marker expression was higher in BTHS cells compared to controls but was unaltered by CpG DNA treatment. Thus, Epstein-Barr virus transformed control and BTHS lymphoblasts fail to increase selected surface markers upon stimulation with LPS and exhibit variable surface marker expression upon stimulation with CpG DNA. Since B lymphocyte surface marker expression upon activation is involved in B cell proliferation and differentiation, cell-cell interaction and the adaptive immune response, we suggest that caution should be exercised when interpreting immunological data obtained from Epstein-Barr virus transformed BTHS cells. Based upon our observations in control cells, our conclusions may be more broadly applicable to other diseases which utilize transformed B lymphocytes for the study of immune biology.