Mitochondria and microbiota dysfunction in COVID-19 pathogenesis

Abstract

The COVID-19 pandemic caused by the coronavirus (SARS-CoV-2) has taken the world by surprise into a major crisis of overwhelming morbidity and mortality. This highly infectious disease is associated with respiratory failure unusual in other coronavirus infections. Mounting evidence link the accelerated progression of the disease in COVID-19 patients to the hyper-inflammatory state termed as the "cytokine storm" involving major systemic perturbations. These include iron dysregulation manifested as hyperferritinemia associated with disease severity. Iron dysregulation induces reactive oxygen species (ROS) production and promotes oxidative stress. The mitochondria are the hub of cellular oxidative homeostasis. In addition, the mitochondria may circulate "cell-free" in non-nucleated platelets, in extracellular vesicles and mitochondrial DNA is found in the extracellular space. The heightened inflammatory/oxidative state may lead to mitochondrial dysfunction leading to platelet damage and apoptosis. The interaction of dysfunctional platelets with coagulation cascades aggravates clotting events and thrombus formation. Furthermore, mitochondrial oxidative stress may contribute to microbiota dysbiosis, altering coagulation pathways and fueling the inflammatory/oxidative response leading to the vicious cycle of events. Here, we discuss various cellular and systemic incidents caused by SARS-CoV-2 that may critically impact intra and extracellular mitochondrial function, and contribute to the progression and severity of the disease. It is crucial to understand how these key modulators impact COVID-19 pathogenesis in the quest to identify novel therapeutic targets that may reduce fatal outcomes of the disease.

Keywords: Extracellular mitochondria; Hyper-inflammation; Hypercoagulability; Iron; Microbiota; Oxidative stress; Platelet mitochondria.

Fig. 1

Mitochondria dysfunction in pathogenesis of COVID-19. A hypothetical scheme describing events initiated by the COVID-19 pro-inflammatory surge of cytokines and ferritin levels leading to oxidative stress and cellular damage. Excess intracellular iron interacts with molecular oxygen, generating reactive oxygen species (ROS) through Haber-Weiss and Fenton reactions and reactive nitrogen species (RNS) and reactive sulfur species (RSS). The mitochondria is the central organelle of ROS generation. Increased ROS generation leads to intra and extra mitochondrial damage which in turn leads to 1) Microbiota dysbiosis and 2) Platelet dysfunction which plays a major role in blood clotting and coagulopathy events. Mitochondrial damage cause the release of contents including proteins, lipids and DNA “spinoffs” that further aggravate the inflammatory response in a vicious cycle of events contributing to COVID-19 disease progression.