Early-Age-Related Changes in Proteostasis Augment Immunopathogenesis of Sepsis and Acute Lung Injury

BACKGROUND: The decline of proteasomal activity is known to be associated with the age-related disorders but the early events involved in this process are not apparent. To address this, we investigated the early-age-related (pediatric vs. adult) mechanisms that augment immunopathogenesis of sepsis and acute lung injury. METHODOLOGY/PRINCIPAL FINDINGS: The 3-weeks (pediatric) and 6-months (adult) old C57BL/6 mice were selected as the study groups. Mice were subjected to 1×20 cecal ligation and puncture (CLP) mediated sepsis or intratracheal Psuedomonas aeruginosa (Pa)-LPS induced acute lung injury (ALI).We observed a significant increase in basal levels of pro-inflammatory cytokine, IL-6 and neutrophil activity marker, myeloperoxidase (MPO) in the adult mice compared to the pediatric indicating the age-related constitutive increase in inflammatory response. Next, we found that age-related decrease in PSMB6 (proteasomal subunit) expression in adult mice results in accumulation of ubiquitinated proteins that triggers the unfolded protein response (UPR). We identified that Pa-LPS induced activation of UPR modifier, p97/VCP (valosin-containing protein) in the adult mice lungs correlates with increase in Pa-LPS induced NFκB levels. Moreover, we observed a constitutive increase in p-eIF2α indicating a protective ER stress response to accumulation of ubiquitinated-proteins. We used MG-132 treatment of HBE cells as an in vitro model to standardize the efficacy of salubrinal (inhibitor of eIF2α de-phosphorylation) in controlling the accumulation of ubiquitinated proteins and the NFκB levels. Finally, we evaluated the therapeutic efficacy of salubrinal to correct proteostasis(definition)-imbalance in the adult mice based on its ability to control CLP induced IL-6 secretion or recruitment of pro-inflammatory cells. CONCLUSIONS/SIGNIFICANCE: Our data demonstrate the critical role of early-age-related proteostasis-imbalance as a novel mechanism that augments the NFκB mediated inflammation in sepsis and ALI. Moreover, our data suggest the therapeutic efficacy of salubrinal in restraining NFκB mediated inflammation in the adult or older subjects.