Non-apoptotic functions of cell death effectors in inflammation and innate immunity

An in vitro cellular model for measuring the impact of thermal stress on Florida reef sponges

Coral reefs are threatened by recurrent mortality incidents in their native habitats brought on by natural and anthropogenic stressors. Elevated temperature has been indicated as a major causing factor. Although ongoing research is focused on corals, sponges are an important benthic organism on coral reefs and are often overlooked. An accurate and standardized method is needed to determine the environmental limits and thresholds of sponges commonly found on coral reefs. We established an in vitro sponge cell model and evaluated the effect of elevated temperatures on primary cell cultures of five common Florida reef sponges-Agelas clathrodes, Aplysina fulva, Cliona varians, Geodia neptuni, and Xestospongia muta. Analysis of the results revealed that the impact of increased temperatures had no significant effect at the cellular level, but there are changes at the molecular level. Shifts in the sponges' transcriptomic profiles induced by increased temperatures, trigger processes related to signal transduction, apoptosis, and cell repair pathways. Further elevation of temperature corresponding to local extremes activated the immune response and programmed cell death. The results of the present study are based on both cellular and molecular data obtained from the in vitro cell model which highlight the minimal response of all five species to thermal stress, providing an insight into the mechanisms involved in the adaptive process. Furthermore, they suggest a resilience of these sponges to the current thermal extremes, but a combination of factors could still lead to a loss of sponges on reefs. This study forms the basis for use of in vitro sponge cell models to evaluate other environmental parameters and stressors on additional sponge species.

Caspases control antiviral innate immunity

Caspases are a family of cysteine proteases whose functions have been scrutinized intensively in recent years. Beyond their established roles in programmed cell death and inflammatory response, some caspases are also fundamental players in antiviral immunity by fine-tuning the levels of antiviral signaling adapters and cytokines, such as type I interferons, which serves as a major, sophisticated weapon against viruses. Viral infections can result in inflammasome activation and the initiation of cell death, including apoptosis and pyroptosis, and multiple caspases are significantly involved in these processes. This review will focus on the cutting-edge discoveries regarding the multifaceted roles of caspases in antiviral innate immunity.

Caspase-8 functions as a key mediator of inflammation and pro-IL-1β processing via both canonical and non-canonical pathways

Caspase-8 is an apical component of cell death pathways. Activated caspase-8 can drive classical caspase-dependent apoptosis and actively inhibits cell death mediated by RIPK3-driven necroptosis. Genetic deletion of Casp8 results in embryonic lethality as a result of uncontrolled necroptosis. This lethality can be rescued by simultaneous deletion of Ripk3. Recently, caspase-8 has been additionally connected to inflammatory pathways within the cell. In particular, caspase-8 has been shown to be crucially involved in the induction of pro-IL-1β synthesis and processing via both non-canonical and canonical pathways. In this review, we bring together current knowledge regarding the role of caspase-8 in cellular inflammation with a particular emphasis on the interplay between caspase-8 and the classical and non-canonical inflammasomes.

Caspase-8 and FLIP regulate RIG-I/MDA5-induced innate immune host responses to picornaviruses

Picornaviruses are small, nonenveloped, positive-stranded RNA viruses, which cause a wide range of animal and human diseases, based on their distinct tissue and cell type tropisms. Myocarditis, poliomyelitis, hepatitis and the common cold are the most significant human illnesses caused by picornaviruses. The host response to picornaviruses is complex, and the damage to tissues occurs not only from direct viral replication within infected cells. Picornaviruses exhibit an exceptional ability to evade the early innate immune response, resulting in chronic infection and autoimmunity. This review discusses the detailed aspects of the early innate host response to picornaviruses infection mediated by RIG-I-like helicases, their adaptor, mitochondrial ant iviral signaling protein, innate immune-induced apoptosis, and the role of caspase-8 and its regulatory paralog, FLIP, in these processes.