Mechanism of lung injury caused by influenza A/H5N1 and the therapeutic effect of mesenchymal stromal cell

Abstract

Severe influenza virus infection could progress to acute lung injury (ALI) where patients suffered from impaired alveolar fluid clearance (AFC) and protein-filled lung edema accumulation. The severe mortality rate of highly pathogenic avian influenza (HPAI) A/H5N1 virus was often associated with the development of ALI. Through understanding the mechanism of influenza virus-induced ALI, the goal was to develop an effective therapeutic treatment for severe human influenza diseases. The hypothesis was that the HPAI A/H5N1-induced pro-inflammatory cytokines could down-regulate the alveolar ion transport to cause the impairment of alveolar fluid clearance (AFC) and alveolar protein permeability (APP). New therapeutic approaches were demanded due to the sub-optimal effect of antivirals on severe human influenza diseases. The multipotent mesenchymal stromal cell (MSC) therapy was proposed as a novel therapy to reduce the H5N1-induced ALI. The hypothesis was that MSCs could resolve the H5N1-impaired AFC and epithelial ion transport through the secretion of paracrine soluble mediators. Another therapeutic strategy proposed was to utilize synthetic ion channel to target the resolution of lung edema. Furthermore, the rapid emergence of novel respiratory viruses urged for advanced risk assessment tools to prepare for potential pandemic threats. A panel of influenza viruses (including wetland surveillance isolates) and coronaviruses was screened for their ability to impair AFC and APP using a physiologically relevant in vitro lung injury model alongside the analysis of tissue tropism using an ex vivo explant culture model of the human respiratory tract.

Influenza A/H5N1 and A/H7N9 viruses reduced AFC and elevated APP when compared to the seasonal A/H1N1 viruses. This dysregulation was found to be associated with the high pro-inflammatory cytokine production by the A/H5N1 virus-infected epithelial cells and the reduced function of epithelial ion channels of CFTR, Na+/K+ATPase, and α-ENaC. The MSCs treatment reversed the AFC impairment and up-regulated the ion channel expression in vitro through the secretion of keratinocyte growth factor and angiopoietin-1. In addition, MSCs improved the survival and lung histopathology of the in vivo A/H5N1-infected mice. Furthermore, the addition of synthetic chloride ion channel C11 attenuated the A/H5N1-impaired AFC and APP without affecting host immune responses in vitro.

The HPAI A/H5N1, A/H7N9, and A/H5N6 viruses highly impaired AFC in vitro whereas the seasonal and the 2009 pandemic A/H1N1 viruses had lesser effects. In addition, all these viruses efficiently infected the ex vivo human lung and bronchus tissues except minimal infection of human bronchi for A/H5N1 virus. The surveillance isolates demonstrated comparable AFC impairment and less tissue tropism than the pandemic A/H1N1 virus. A stronger lung tissue tropism and more severe AFC impairment implied a higher risk of severe lung disease whereas a more prominent bronchus tissue tropism pertained to a greater inter-species transmission.

In conclusion, the life-threatening complication of ALI demanded effective and sustainable treatment. Novel strategies of MSC and synthetic ion channel on influenza A/H5N1-impaired lung edema clearance were proposed for severe influenza virus-induced ALI. Both the therapeutic study and risk assessment of disease severity and virus pathogenesis were initiated in preparation for future outbreaks and pandemics.