Dynamic regulation of cardiolipin by the lipid pump Atp8b1 determines the severity of lung injury in experimental pneumonia

Abstract

Pneumonia remains the leading cause of infectious deaths and yet fundamentally new conceptual models underlying its pathogenesis have not emerged. Patients and mice with bacterial pneumonia have marked elevations of cardiolipin in lung fluid, a rare, mitochondrial-specific phospholipid that potently disrupts surfactant function. Intratracheal cardiolipin in mice recapitulates the clinical phenotype of pneumonia including impaired lung mechanics, modulation of cell survival and cytokine networks, and lobar consolidation. We have identified and characterized the activity of a novel cardiolipin transporter, ATP8b1, a mutant version of which is associated with severe pneumonia in humans and mice. ATP8b1 bound and internalized cardiolipin from extracellular fluid via a basic residue-enriched motif. Administration of cardiolipin binding motif peptide or ATP8b1 gene transfer in mice lessened lung injury and improved survival. The results unveil a new paradigm whereby ATP8b1 is a cardiolipin importer but its capacity to remove cardiolipin from lung fluid is exceeded during inflammation or ATP8b1 inefficiency. This discovery opens the door for new therapeutic strategies directed at modulating cardiolipin levels or its molecular interactions in pneumonia.

Phospholipid Flippase Activities and Substrate Specificities of Human Type IV P-type ATPases Localized to the Plasma Membrane

“…1) In Caco-2 cells, depletion of ATP8B1 by RNAi was reported to have no effect on PS translocation (22). 2) Another study proposed that ATP8B1 acts as a cardiolipin importer (23). Therefore, it remains uncertain whether PS is a bona fide substrate for ATP8B1.…”

“…A previous study reported that exogenous expression of ATP8B1 in the CHO-K1 mutant cell line UPS-1, which is defective in PS translocation, promoted PS translocation from the exoplasmic to the cytoplasmic leaflet (8). In contrast, depletion of ATP8B1 by RNAi had no effect on PS translocation in Caco-2 cells (22), and another study proposed that ATP8B1 acts as a cardiolipin importer (23). Therefore, it remains uncertain whether PS is a bona fide substrate of ATP8B1.…”

Genetically manipulated mouse models of lung disease: potential and pitfalls

“…CCSP is synthesized and expressed primarily in the larger airway and proximal epithelial cells of the lung (ϳ40% of airway epithelial cells), whereas SPC is synthesized and secreted predominantly by the more distal type II alveolar epithelial cells. To target larger airway-specific expression in adult mice, a 2.3-kb rat CCSP promoter was engineered and has been widely used (127), and, similarly, to target more distal airway-specific expression a 3.7-kb human SPC promoter was generated and has also been widely used (165).…”

LPS impairs oxygen utilization in epithelia by triggering degradation of the mitochondrial enzyme Alcat1

“…Deficiency of cardiolipin is lethal, resulting in apoptosis, impaired proliferation and reduced energy stores (Kagan et al, 2009;Kirkland et al, 2002;Martens et al, 2014;Sorice et al, 2004). Extracellular cardiolipin levels, such as in lung fluid, are very low, but release of cardiolipin from damaged mitochondria or bacterial membranes into the lung can serve as a damage-associated molecular pattern, causing host cell death under some pathophysiological conditions (Ray et al, 2010). Therefore, tight maintenance of cardiolipin homeostasis is crucial.…”