miR-221-5p-Mediated Downregulation of JNK2 Aggravates Acute Lung Injury

Sepsis and acute lung injury (ALI) are linked to mitochondrial dysfunction; however, the underlying mechanism remains elusive. We previously reported that c-Jun N-terminal protein kinase 2 (JNK2) promotes stress-induced mitophagy by targeting small mitochondrial alternative reading frame (smARF) for ubiquitin-mediated proteasomal degradation, thereby preventing mitochondrial dysfunction and restraining inflammasome activation. Here we report that loss of JNK2 exacerbates lung inflammation and injury during sepsis and ALI in mice. JNK2 is downregulated in mice with endotoxic shock or ALI, concomitantly correlated inversely with disease severity. Small RNA sequencing revealed that miR-221-5p, which contains seed sequence matching to JNK2 mRNA 3’ untranslated region (3’UTR), is upregulated in response to lipopolysaccharide, with dynamically inverse correlation with JNK2 mRNA levels. miR-221-5p targets the 3’UTR of JNK2 mRNA leading to its downregulation. Accordingly, miR-221-5p exacerbates lung inflammation and injury during sepsis in mice by targeting JNK2. Importantly, in patients with pneumonia in medical intensive care unit, JNK2 mRNA levels in alveolar macrophages flow sorted from non-bronchoscopic broncholaveolar lavage (BAL) fluid were inversely correlated strongly and significantly with the percentage of neutrophils, neutrophil and white blood cell counts in BAL fluid. Our data suggest that miR-221-5p targets JNK2 and thereby aggravates lung inflammation and injury during sepsis.

The Role of TRPV4 in Regulating Innate Immune Cell Function in Lung Inflammation

Ion channels/pumps are essential regulators of innate immune cell function. Macrophages have been increasingly recognized to have phenotypic plasticity and location-specific functions in the lung. Transient receptor potential vanilloid 4 (TRPV4) function in lung injury has been shown to be stimulus- and cell-type specific. In the current review, we discuss the importance of TRPV4 in macrophages and its role in phagocytosis and cytokine secretion in acute lung injury/acute respiratory distress syndrome (ARDS). Furthermore, TRPV4 controls a MAPK molecular switch from predominately c-Jun N-terminal kinase, JNK activation, to that of p38 activation, that mediates phagocytosis and cytokine secretion in a matrix stiffness-dependent manner. Expanding knowledge regarding the downstream mechanisms by which TRPV4 acts to tailor macrophage function in pulmonary inflammatory diseases will allow for formulation of novel therapeutics.