Rethinking cholera pathogenesis- No longer all in the same "camp"

SARS-CoV-2 may hijack GPCR signaling pathways to dysregulate lung ion and fluid transport

The tropism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a virus responsible for the ongoing coronavirus disease 2019 (COVID-19) pandemic, toward the host cells is determined, at least in part, by the expression and distribution of its cell surface receptor, angiotensin-converting enzyme 2 (ACE2). The virus further exploits the host cellular machinery to gain access into the cells; its spike protein is cleaved by a host cell surface transmembrane serine protease 2 (TMPRSS2) shortly after binding ACE2, followed by its proteolytic activation at a furin cleavage site. The virus primarily targets the epithelium of the respiratory tract, which is covered by a tightly regulated airway surface liquid (ASL) layer that serves as a primary defense mechanism against respiratory pathogens. The volume and viscosity of this fluid layer is regulated and maintained by a coordinated function of different transport pathways in the respiratory epithelium. We argue that SARS-CoV-2 may potentially alter evolutionary conserved second-messenger signaling cascades via activation of G protein-coupled receptors (GPCRs) or by directly modulating G protein signaling. Such signaling may in turn adversely modulate transepithelial transport processes, especially those involving cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial Na⁺ channel (ENaC), thereby shifting the delicate balance between anion secretion and sodium absorption, which controls homeostasis of this fluid layer. As a result, activation of the secretory pathways including CFTR-mediated Cl⁻ transport may overwhelm the absorptive pathways, such as ENaC-dependent Na⁺ uptake, and initiate a pathophysiological cascade leading to lung edema, one of the most serious and potentially deadly clinical manifestations of COVID-19.

Clostridioides difficile: Sometimes It Pays To Be Difficult

In this issue of Cell Host & Microbe, publications from Bushman et al. (2020) and Knippel et al. (2020) outline elements of host epithelial damage or inflammation that Clostridioides difficile subverts, enabling continued growth. These mechanisms provide insight into how this important pathogen influences the gut environment to promote its metabolic strategy during infection.