Aging of the world population and a concomitant increase in age-related diseases and disabilities mandates the search for strategies to increase healthspan, the length of time an individual lives healthy and productively. Due to the age-related decline of the immune system, infectious diseases remain among the top 5-10 causes of mortality and morbidity in the elderly, and improving immune function during aging remains an important aspect of healthspan extension. Calorie restriction (CR) and more recently rapamycin (rapa) feeding have both been used to extend lifespan in mice. Preciously few studies have actually investigated the impact of each of these interventions upon in vivo immune defense against relevant microbial challenge in old organisms. We tested how rapa and CR each impacted the immune system in adult and old mice. We report that each intervention differentially altered T-cell development in the thymus, peripheral T-cell maintenance, T-cell function and host survival after West Nile virus infection, inducing distinct but deleterious consequences to the aging immune system. We conclude that neither rapa feeding nor CR, in the current form/administration regimen, may be optimal strategies for extending healthy immune function and, with it, lifespan.
Salivary gland inflammation is a hallmark of Sjögren's syndrome (SS), a common autoimmune disease characterized by lymphocytic infiltration of the salivary gland and loss of saliva secretion, predominantly in women. The P2X7 receptor (P2X7R) is an ATP-gated nonselective cation channel that induces inflammatory responses in cells and tissues, including salivary gland epithelium. In immune cells, P2X7R activation induces the production of proinflammatory cytokines, including IL-1β and IL-18, by inducing the oligomerization of the multiprotein complex NLRP3-type inflammasome. Here, our results show that in primary mouse submandibular gland (SMG) epithelial cells, P2X7R activation also induces the assembly of the NLRP3 inflammasome and the maturation and release of IL-1β, a response that is absent in SMG cells isolated from mice deficient in P2X7Rs (P2X7R-/-). P2X7R-mediated IL-1β release in SMG epithelial cells is dependent on transmembrane Na+ and/or K+ flux and the activation of heat shock protein 90 (HSP90), a protein required for the activation and stabilization of the NLRP3 inflammasome. Also, using the reactive oxygen species (ROS) scavengers N-acetyl cysteine and Mito-TEMPO, we determined that mitochondrial reactive oxygen species are required for P2X7R-mediated IL-1β release. Lastly, in vivo administration of the P2X7R antagonist A438079 in the CD28-/-, IFNγ-/-, NOD.H-2h4 mouse model of salivary gland exocrinopathy ameliorated salivary gland inflammation and enhanced carbachol-induced saliva secretion. These findings demonstrate that P2X7R antagonism in vivo represents a promising therapeutic strategy to limit salivary gland inflammation and improve secretory function.
Autophagy is a catabolic process that has been shown to have a role in many cellular processes including the removal of excessive or damaged proteins and protein aggregates. The salivary glands play a critical role in oral health, and their secretory capacity may be critically intertwined with the autophagic process. This review describes the role of autophagy activation in normal salivary gland homeostasis and during the glandular stress responses of therapeutic radiation, ductal ligation, autoimmunity, and salivary gland adenoid cystic carcinoma.
Autophagy maintains cell and tissue homeostasis through catabolic degradation. To better delineate the in vivo function for autophagy in adaptive responses to tissue injury, we examined the impact of compromised autophagy in mouse submandibular glands (SMGs) subjected to main excretory duct ligation. Blocking outflow from exocrine glands causes glandular atrophy by increased ductal pressure. Atg5(f/-);Aqp5-Cre mice with salivary acinar-specific knockout (KO) of autophagy essential gene Atg5 were generated. While duct ligation induced autophagy and the expression of inflammatory mediators, SMGs in Atg5(f/-);Aqp5-Cre mice, before ligation, already expressed higher levels of proinflammatory cytokine and Cdkn1a/p21 messages. Extended ligation period resulted in the caspase-3 activation and acinar cell death, which was delayed by Atg5 knockout. Moreover, expression of a set of senescence-associated secretory phenotype (SASP) factors was elevated in the post-ligated glands. Dysregulation of cell-cycle inhibitor CDKN1A/p21 and activation of senescence-associated β-galactosidase were detected in the stressed SMG duct cells. These senescence markers peaked at day 3 after ligation and partially resolved by day 7 in post-ligated SMGs of wild-type (WT) mice, but not in KO mice. The role of autophagy-related 5 (ATG5)-dependent autophagy in regulating the tempo, duration and magnitude of cellular stress responses in vivo was corroborated by in vitro studies using MEFs lacking ATG5 or autophagy-related 7 (ATG7) and autophagy inhibitors. Collectively, our results highlight the role of ATG5 in the dynamic regulation of ligation-induced cellular senescence and apoptosis, and suggest the involvement of autophagy resolution in salivary repair.
Radiotherapy of head and neck cancers often results in collateral damage to adjacent salivary glands associated with clinically significant hyposalivation and xerostomia. Due to the reduced capacity of salivary glands to regenerate, hyposalivation is treated by substitution with artificial saliva, rather than through functional restoration of the glands. During embryogenesis, the ectodysplasin/ectodysplasin receptor (EDA/EDAR) signaling pathway is a critical element in the development and growth of salivary glands. We have assessed the effects of pharmacological activation of this pathway in a mouse model of radiation-induced salivary gland dysfunction. We report that post-irradiation administration of an EDAR-agonist monoclonal antibody (mAbEDAR1) normalizes function of radiation damaged adult salivary glands as determined by stimulated salivary flow rates. In addition, salivary gland structure and homeostasis is restored to pre-irradiation levels. These results suggest that transient activation of pathways involved in salivary gland development could facilitate regeneration and restoration of function following damage.