Mitochondrial metabolic manipulation by SARS-CoV-2 in peripheral blood mononuclear cells of patients with COVID-19

Abstract

The COVID-19 pandemic has been the primary global health issue since its outbreak in December 2019. Patients with metabolic syndrome suffer from severe complications and a higher mortality rate due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We recently proposed that SARS-CoV-2 can hijack host mitochondrial function and manipulate metabolic pathways for their own advantage. The aim of the current study was to investigate functional mitochondrial changes in live peripheral blood mononuclear cells (PBMCs) from patients with COVID-19 and to decipher the pathways of substrate utilization in these cells and corresponding changes in the inflammatory pathways. We demonstrate mitochondrial dysfunction, metabolic alterations with an increase in glycolysis, and high levels of mitokine in PBMCs from patients with COVID-19. Interestingly, we found that levels of fibroblast growth factor 21 mitokine correlate with COVID-19 disease severity and mortality. These data suggest that patients with COVID-19 have a compromised mitochondrial function and an energy deficit that is compensated by a metabolic switch to glycolysis. This metabolic manipulation by SARS-CoV-2 triggers an enhanced inflammatory response that contributes to the severity of symptoms in COVID-19. Targeting mitochondrial metabolic pathway(s) can help define novel strategies for COVID-19.

Keywords: COVID-19; SARS-CoV-2; glycolysis; mitochondrial dysfunction; mitokines.

Figure. 1.

Mitochondrial dysfunction in live peripheral blood mononuclear cells (PBMCs) from patients with COVID-19. Cellular mitochondrial profile in human PBMCs of healthy controls (HC) (n = 6), patients with PCR-positive COVID-19 (n = 6), and patients with chest infection (negative for COVID-19; n = 7). Well-defined inhibitors, oligomycin (Oligo), carbonyl cyanide 4-[trifluoromethoxy] phenylhydrazone (FCCP), and rotenone (Rot)/antimycin A (Anti A) are used in the Mito Stress Test Kit. PBMCs from participants were isolated and seeded at 3 × 10⁵ cells/well, and the Seahorse XFp extracellular flux analyzer was used to measure basal respiration (Resp; A), ATP-linked respiration (B), maximal respiration (C), reserve capacity (D), nonmitochondria production (E), and proton leak (F). Data are presented as means ± SD and analyzed by one-way ANOVA with Tukey’s test where *P < 0.05, **P < 0.01. OCR, oxygen consumption rate.

Figure. 2.

Phenotype Stress Test showing high basal and stressed glycolysis in peripheral blood mononuclear cells (PBMCs) from patients with COVID-19: live PBMCs from healthy controls (HC) (n = 6), patients with PCR-positive COVID-19 (n = 5), and patients with chest infection (Chest inf; negative for COVID-19; n = 7) were seeded at 3 × 10⁵ cells/well, and the Seahorse XFp extracellular flux analyzer was used to measure in a real-time assay their baseline and stressed metabolic phenotype. This 1-h test measured both the mitochondrial (A and B) and glycolytic activity (C and D) of the cells and their baseline values with metabolic activity under stressed conditions. Data are presented as means ± SD and analyzed by one-way ANOVA with Tukey’s test where *P < 0.05, **P < 0.01. ECAR, extracellular acidification rate; OCR, oxygen consumption rate.

Figure. 3.

Substrate Oxidation Stress Test interrogates three primary substrates that drive the mitochondrial activities: long-chain fatty acids (LCFAs), glucose/pyruvate, and/or glutamine in peripheral blood mononuclear cells (PBMCs) from patients with COVID-19: live PBMCs from patients with COVID-19 (n = 5) were analyzed by using the Seahorse XFp analyzer to measure in a real-time assay comprehensive mitochondrial assessment enabled by the XF Cell Mito Stress Test with inhibitors of specific substrate oxidation pathways. A: bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl) ethyl sulfide (BPTES) was used for inhibition of glutamine through glutaminase 1 (GLS-1). B: etomoxir (Eto) was used for inhibition of LCFAs through inhibition of carnitine palmitoyltransferase 1a (CPT1a). C: UK5099 was used for inhibition of glucose or pyruvate through inhibition of the mitochondrial pyruvate carrier (MPC). Cells are interrogated under not only lower substrate demand (i.e., basal respiration) but also higher substrate demand conditions (i.e., maximal respiration) where critical substrate dependence is revealed. Data presented are the representative run for each inhibitor in PBMCs of patients with COVID-19. FCCP, carbonyl cyanide 4-[trifluoromethoxy] phenylhydrazone; OCR, oxygen consumption rate.

Figure. 4.

Circulating levels of fibroblast growth factor 21 (FGF-21), a mitokine, in healthy controls (HCs), patients with COVID-19, and patients with chest infection (Chest inf), and its correlation with mitochondrial functional parameters. A: plasma concentrations of FGF-21 were measured by ELISA in HCs (n = 9), patients with PCR-positive COVID-19 (n = 6), and patients with chest infection (negative for COVID-19; n = 7). B: FGF-21 levels in plasma of HC (n = 9) vs. plasma of patients who died due to COVID-19 (n = 5). C: schematic representation of the increasing trend of FGF-21 levels with severity of disease in patients with COVID-19. D: correlation matrix of FGF-21 and mitochondrial functional parameters (reserve capacity, maximal respiration, and ATP-linked respiration). Data are represented as means ± SD, ***P < 0.001.

Figure. 5.

Circulating levels of interleukin-6 (IL-6) in healthy controls (HCs), patients with COVID-19, and patients with chest infection. A: plasma concentrations of IL-6 were measured by ELISA in HCs (n = 5), patients with PCR-positive COVID-19 (n = 6), and patients with chest infection (negative for COVID-19; n = 7). B: IL-6 levels in plasma of HC vs. plasma of patients who died due to COVID-19 (n = 5). Data are represented as means ± SD, **P < 0.01.