Targeting the amplification loop between mitochondria and complement activation in acute respiratory distress syndrome (ARDS)

Hrishikesh Kulkarni, M.D., MSCI

Abstract:

The overarching goal of this project is to enhance both the survival and quality of life after acute respiratory distress syndrome (ARDS), a major cause of mortality due to both infectious and sterile causes.

Infectious causes of ARDS include pneumonia (bacterial and viral etiologies, i.e., COVID-19) and sterile causes include ischemia-reperfusion injury after lung transplantation. However, the immune-mediated changes that incite and propagate acute lung injury (the pathological correlate of ARDS) are largely unknown. Cell death during ARDS results in the release of damage-associated molecular patterns (DAMPs) that perpetuate inflammation and ongoing tissue injury, including mitochondrial DNA (MtDNA). In line with this observation, we have reported that local and circulating MtDNA independently associate with both infectious and sterile ARDS. Like mitochondria, the complement system is an evolutionary conserved aspect of our human body, is a critical component of the innate immune response, and is activated within minutes of tissue injury. Complement activation is critical to propagating ARDS in certain settings, including lung transplantation and COVID-19 pneumonia.

Our preliminary data suggest a strong correlation between MtDNA and complement activation in ARDS. Thus, although there appears to be an association between these two evolutionarily conserved markers of inflammation, it remains unclear if the recognition of mitochondrial DAMPs by the complement system promotes tissue inflammation leading to ARDS. If true, these early inciting events contributing to ARDS can be interrupted, thus providing targets for a currently irreversible disease. We hypothesize that mitochondrial DAMPs drive complement activation leading to ARDS.

We propose the following Specific Aims: (1) dissect pathways by which mitochondria released from the lung during injury activate complement, and (2) assess how complement modulates mitochondrial respiration and homeostasis during lung epithelial injury. As a part of Aim 1, we will address if mitochondria derived from human alveolar epithelial cells activate complement, and will identify the predominant pathways by which they activate the complement cascade (i.e., classical, lectin or alternative). Subsequently, cell-free mitochondria isolated from the bronchial fluid of patients with sterile (i.e., primary graft dysfunction after lung transplantation) and infectious (i.e., pneumonia) injury will be also assayed for the ability to activate complement. As a part of Aim 2, we will assess how complement modulates cellular mitochondrial activity during lung epithelial injury. Utilizing live-cell imaging of a human alveolar epithelial cell line, we will determine if intracellular accumulation of complement proteins modulates mitochondrial dysfunction and mitophagy in the setting of sterile (i.e., oxidative stress) and infectious (i.e., Pseudomonas) injury. Hence, through this proposal, we will decipher the mechanisms by which prognosticators of ARDS disease progression — which have been identified by us in models of sterile and infectious injury — contribute to ongoing tissue damage, with the ultimate goal of mitigating severe lung disease.