Activation of the AIM2 Receptor in Circulating Cells of Post-COVID-19 Patients With Signs of Lung Fibrosis Is Associated With the Release of IL-1α, IFN-α and TGF-β

New insights into nucleic acid sensor AIM2: The potential benefit in targeted therapy for cancer

The AIM2 inflammasome represents a multifaceted oligomeric protein complex within the innate immune system, with the capacity to perceive double-stranded DNA (dsDNA) and engage in diverse physiological reactions and disease contexts, including cancer. While originally conceived as a discerning DNA sensor, AIM2 has demonstrated its capability to discern various nucleic acid variations, encompassing RNA and DNA-RNA hybrids. Through its interaction with nucleic acids, AIM2 orchestrates the assembly of a complex involving multiple proteins, aptly named the AIM2 inflammasome, which facilitates the enzymatic cleavage of proinflammatory cytokines, namely pro-IL-1β and pro-IL-18. This process, in turn, underpins its pivotal biological role. In this review, we provide a systematic summary and discussion of the latest advancements in AIM2 sensing various types of nucleic acids. Additionally, we discuss the modulation of AIM2 activation, which can cause cell death, including pyroptosis, apoptosis, and autophagic cell death. Finally, we fully illustrate the evidence for the dual role of AIM2 in different cancer types, including both anti-tumorigenic and pro-tumorigenic functions. Considering the above information, we uncover the therapeutic promise of modulating the AIM2 inflammasome in cancer treatment.

Absent in melanoma 2 (AIM2) positive profile identifies a poor prognosis of lung adenocarcinoma patients

The absent in melanoma 2 (AIM2) inflammasome has been demonstrated as involved in tumor growth. In this study we used human samples of lung adenocarcinoma (LUAD) patients, taking advantage of a mouse model of smoking cessation. Human samples were stratified according to the smoking status, high-risk factor for this type of tumor. Both public transcriptomic and human samples obtained by a clinical trial proved that AIM2 was upregulated either in terms of mRNA or protein, respectively, in the tumor mass according to the TNM stage, but it did not relate to the smoking status, age and sex. The upregulation of AIM2 was correlated to an immunosuppressive environment according to resting/non-active dendritic cells (DCs) and T regulatory cells, as demonstrated in both human samples and by means of an experimental model of smoking mice. Computational analysis showed that AIM2 upregulation was correlated to both an inflammasome profile, responsible for the poor prognosis of non-smoker and smoker LUAD patients, and to a non-inflammasome profile for former smoker. In conclusion, our study demonstrated that AIM2 is involved in lung carcinogenesis either in a canonical and non-canonical manner due to an immunosuppressive microenvironment associated to a dismal prognosis of LUAD patients.

Breaking Bad: Inflammasome Activation by Respiratory Viruses

The nucleotide-binding domain leucine-rich repeat-containing receptor (NLR) family is a group of intracellular sensors activated in response to harmful stimuli, such as invading pathogens. Some NLR family members form large multiprotein complexes known as inflammasomes, acting as a platform for activating the caspase-1-induced canonical inflammatory pathway. The canonical inflammasome pathway triggers the secretion of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 by the rapid rupture of the plasma cell membrane, subsequently causing an inflammatory cell death program known as pyroptosis, thereby halting viral replication and removing infected cells. Recent studies have highlighted the importance of inflammasome activation in the response against respiratory viral infections, such as influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While inflammasome activity can contribute to the resolution of respiratory virus infections, dysregulated inflammasome activity can also exacerbate immunopathology, leading to tissue damage and hyperinflammation. In this review, we summarize how different respiratory viruses trigger inflammasome pathways and what harmful effects the inflammasome exerts along with its antiviral immune response during viral infection in the lungs. By understanding the crosstalk between invading pathogens and inflammasome regulation, new therapeutic strategies can be exploited to improve the outcomes of respiratory viral infections.

Inflammasomes during SARS-CoV-2 infection and development of their corresponding inhibitors

Corona Virus Disease 2019 (COVID-19) continues to be a burden for human health since its outbreak in Wuhan, China in December 2019. Recently, the emergence of new variants of concerns (VOCs) is challenging for vaccines and drugs efficiency. In severe cases, SARS-CoV-2 provokes inappropriate hyperinflammatory immune responses leading to acute respiratory distress syndrome (ARDS) and even death. This process is regulated by inflammasomes which are activated after binding of the viral spike (S) protein to cellular angiotensin-converting enzyme 2 (ACE2) receptor and triggers innate immune responses. Therefore, the formation of "cytokines storm" leads to tissue damage and organ failure. NOD-like receptor family pyrin domain containing 3 (NLRP3) is the best studied inflammasome known to be activated during SARS-CoV-2 infection. However, some studies suggest that SARS-CoV-2 infection is associated with other inflammasomes as well; such as NLRP1, absent in melanoma-2 (AIM-2), caspase-4 and -8 which were mostly found during dsRNA virus or bacteria infection. Multiple inflammasome inhibitors that exist for other non-infectious diseases have the potential to be used to treat severe SARS-CoV-2 complications. Some of them have showed quite encouraging results during pre- and clinical trials. Nevertheless, further studies are in need for the understanding and targeting of SARS-Cov-2-induced inflammasomes; mostly an update of its role during the new VOCs infection is necessary. Hence, this review highlights all reported inflammasomes involved in SARS-CoV-2 infection and their potential inhibitors including NLRP3- and Gasdermin D (GSDMD)-inhibitors. Further strategies such as immunomodulators and siRNA are also discussed. As highly related to COVID-19 severe cases, developing inflammasome inhibitors holds a promise to treat severe COVID-19 syndrome effectively and reduce mortality.

Cytoplasmic DNAs: Sources, sensing, and roles in the development of lung inflammatory diseases and cancer

Cytoplasmic DNA is emerging as a pivotal contributor to the pathogenesis of inflammatory diseases and cancer, such as COVID-19 and lung carcinoma. However, the complexity of various cytoplasmic DNA-related pathways and their crosstalk remains challenging to distinguish their specific roles in many distinct inflammatory diseases, especially for the underlying mechanisms. Here, we reviewed the latest findings on cytoplasmic DNA and its signaling pathways in inflammatory lung conditions and lung cancer progression. We found that sustained activation of cytoplasmic DNA sensing pathways contributes to the development of common lung diseases, which may result from external factors or mutations of key genes in the organism. We further discussed the interplays between cytoplasmic DNA and anti-inflammatory or anti-tumor effects for potential immunotherapy. In sum, this review aids in understanding the roles of cytoplasmic DNAs and exploring more therapeutic strategies.

Hyperinflammatory Response in COVID-19: A Systematic Review

COVID-19 is a multisystemic disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The immunopathogenic conditions of the hyperinflammatory response that cause systemic inflammation are extremely linked to its severity. This research sought to review the immunopathological elements that contribute to its progression. This is a systematic review using the PUBMED, LILACS, MEDLINE, and SCIELO databases using articles between May 2020 and July 2022 with the following search terms in conjunction with "AND": "SARS-CoV-2"; "COVID-19"; "ARDS" and "Cytokine Storm". The quality appraisal and risk of bias were assessed by the JBI checklists and the Cochrane Collaboration's RoB 2.0 and ROBINS-I tools, respectively, and the risk of bias for in vitro studies by a pre-defined standard in the literature. The search resulted in 39 articles. The main actors in this response denote SARS-CoV-2 Spike proteins, cellular proteases, leukocytes, cytokines, and proteolytic cascades. The "cytokine storm" itself brings several complications to the host through cytokines such as IL-6 and chemokines (such as CCL2), which influence tissue inflammation through apoptosis and pyroptosis. The hyperinflammatory response causes several unfavorable outcomes in patients, and systemic inflammation caused largely by the dysregulation of the immune response should be controlled for their recovery.

Microvascular significance of TGF-β axis activation in COVID-19

As 2023 approaches, the COVID-19 pandemic has killed millions. While vaccines have been a crucial intervention, only a few effective medications exist for prevention and treatment of COVID-19 in breakthrough cases or in unvaccinated or immunocompromised patients. SARS-CoV-2 displays early and unusual features of micro-thrombosis and immune dysregulation that target endothelial beds of the lungs, skin, and other organs. Notably, anticoagulation improves outcomes in some COVID-19 patients. The protein transforming growth factor-beta (TGF-β1) has constitutive roles in maintaining a healthy microvasculature through its roles in regulating inflammation, clotting, and wound healing. However, after infection (including viral infection) TGF-β1 activation may augment coagulation, cause immune dysregulation, and direct a path toward tissue fibrosis. Dysregulation of TGF-β signaling in immune cells and its localization in areas of microvascular injury are now well-described in COVID-19, and such events may contribute to the acute respiratory distress syndrome and skin micro-thrombosis outcomes frequently seen in severe COVID-19. The high concentration of TGF-β in platelets and in other cells within microvascular thrombi, its ability to activate the clotting cascade and dysregulate immune pathways, and its pro-fibrotic properties all contribute to a unique milieu in the COVID-19 microvasculature. This unique environment allows for propagation of microvascular clotting and immune dysregulation. In this review we summarize the physiological functions of TGF-β and detail the evidence for its effects on the microvasculature in COVID-19. In addition, we explore the potential role of existing TGF-β inhibitors for the prevention and treatment of COVID-19 associated microvascular thrombosis and immune dysregulation.

Examination of the role of necroptotic damage-associated molecular patterns in tissue fibrosis

Fibrosis is defined as the abnormal and excessive deposition of extracellular matrix (ECM) components, which leads to tissue or organ dysfunction and failure. However, the pathological mechanisms underlying fibrosis remain unclear. The inflammatory response induced by tissue injury is closely associated with tissue fibrosis. Recently, an increasing number of studies have linked necroptosis to inflammation and fibrosis. Necroptosis is a type of preprogrammed death caused by death receptors, interferons, Toll-like receptors, intracellular RNA and DNA sensors, and other mediators. These activate receptor-interacting protein kinase (RIPK) 1, which recruits and phosphorylates RIPK3. RIPK3 then phosphorylates a mixed lineage kinase domain-like protein and causes its oligomerization, leading to rapid plasma membrane permeabilization, the release of cellular contents, and exposure of damage-associated molecular patterns (DAMPs). DAMPs, as inflammatory mediators, are involved in the loss of balance between extensive inflammation and tissue regeneration, leading to remodeling, the hallmark of fibrosis. In this review, we discuss the role of necroptotic DAMPs in tissue fibrosis and highlight the inflammatory responses induced by DAMPs in tissue ECM remodeling. By summarizing the existing literature on this topic, we underscore the gaps in the current research, providing a framework for future investigations into the relationship among necroptosis, DAMPs, and fibrosis, as well as a reference for later transformation into clinical treatment.