NLRP3 inflammasome signaling is activated by low-level lysosome disruption but inhibited by extensive lysosome disruption: roles for K+ efflux and Ca2+ influx.

Nucleotide-binding domain, leucine-rich-repeat-containing family, pyrin domain-containing 3 (NLRP3) is a cytosolic protein that nucleates assembly of inflammasome signaling platforms, which facilitate caspase-1-mediated IL-1ß release and other inflammatory responses in myeloid leukocytes. NLRP3 inflammasomes are assembled in response to multiple pathogen- or environmental stress-induced changes in basic cell physiology, including the destabilization of lysosome integrity and activation of K(+)-permeable channels/transporters in the plasma membrane (PM). However, the quantitative relationships between lysosome membrane permeabilization (LMP), induction of increased PM K(+) permeability, and activation of NLRP3 signaling are incompletely characterized. We used Leu-Leu-O-methyl ester (LLME), a soluble lysosomotropic agent, to quantitatively track the kinetics and extent of LMP in relation to NLRP3 inflammasome signaling responses (ASC oligomerization, caspase-1 activation, IL-1ß release) and PM cation fluxes in murine bone marrow-derived dendritic cells (BMDCs). Treatment of BMDCs with submillimolar (≤1 mM) LLME induced slower and partial increases in LMP that correlated with robust NLRP3 inflammasome activation and K(+) efflux. In contrast, supramillimolar (≥2 mM) LLME elicited extremely rapid and complete collapse of lysosome integrity that was correlated with suppression of inflammasome signaling. Supramillimolar LLME also induced dominant negative effects on inflammasome activation by the canonical NLRP3 agonist nigericin; this inhibition correlated with an increase in NLRP3 ubiquitination. LMP elicited rapid BMDC death by both inflammasome-dependent pyroptosis and inflammasome-independent necrosis. LMP also triggered Ca(2+) influx, which attenuated LLME-stimulated NLRP3 inflammasome signaling but potentiated LLME-induced necrosis. Taken together, these studies reveal a previously unappreciated signaling network that defines the coupling between LMP, changes in PM cation fluxes, cell death, and NLRP3 inflammasome activation.

Claudin-23 reshapes epithelial tight junction architecture to regulate barrier function.

Claudin family tight junction proteins form charge- and size-selective paracellular channels that regulate epithelial barrier function. In the gastrointestinal tract, barrier heterogeneity is attributed to differential claudin expression. Here, we show that claudin-23 (CLDN23) is enriched in luminal intestinal epithelial cells where it strengthens the epithelial barrier. Complementary approaches reveal that CLDN23 regulates paracellular ion and macromolecule permeability by associating with CLDN3 and CLDN4 and regulating their distribution in tight junctions. Computational modeling suggests that CLDN23 forms heteromeric and heterotypic complexes with CLDN3 and CLDN4 that have unique pore architecture and overall net charge. These computational simulation analyses further suggest that pore properties are interaction-dependent, since differently organized complexes with the same claudin stoichiometry form pores with unique architecture. Our findings provide insight into tight junction organization and propose a model whereby different claudins combine to form multiple distinct complexes that modify epithelial barrier function by altering tight junction structure.

Challenges and Effects of the COVID-19 Pandemic on Asylum Seeker Health at the U.S.-Mexico Border.

Purpose: The coronavirus disease 2019 (COVID-19) pandemic presents health care challenges to asylum seekers living in congregate encampments, including those along the U.S.-Mexico border. It is necessary to understand the impact of the pandemic among this population to address health care needs, reduce transmission, and diminish COVID-19-related morbidity. Methods: Thirty interviews were conducted with asylum seekers and health care professionals in a temporary camp in Matamoros, Mexico to determine challenges, perceptions, and effects of the COVID-19 pandemic. Interviews were coded in NVivo12 by using a team-based approach. Results: The pandemic caused significant mental health burdens but no perceived adverse physical effects, with the U.S. border closure and health care access barriers as more pressing concerns. Participants reported access to information about COVID-19 but had varied levels of knowledge and adherence to disease reduction strategies due to camp conditions. Most participants believed that they had special protection from COVID-19, including strong immune systems or from God. The nongovernmental organizations providing health care and sanitation faced multiple challenges to implement new policies to manage COVID-19. The institution of required temperature checks and quarantine of COVID-19 positive patients led to distrust, decreased seeking of health care services among asylum seekers, and possible underreporting of COVID-19 cases. Conclusion: Our findings among asylum seekers in a Matamoros camp highlight the challenges to implementing disease reduction policies in low-resource congregate camps. Policies to address disease outbreaks focusing on the social determinants of health, health care access barriers, and community engagement may be more acceptable to asylum seekers, suggesting the need for effective strategies to provide prevention information that complements such measures.