Genomic DNA activates the AIM2 inflammasome and STING pathways to induce inflammation in lacrimal gland myoepithelial cells

The role of AIM2 in inflammation and tumors

Absent in melanoma 2 (AIM2) serves as an intracellular nucleic acid sensor that predominantly detects double-stranded DNA (dsDNA) within the cells. This detection initiates the assembly of inflammasome and activates the inflammasome signaling cascade, resulting in the production of inflammatory mediators and the cleavage of Gasdermins. Consequently, these processes culminate in inflammatory responses and pyroptotic cell death. AIM2 plays a pivotal role in modulating inflammation and tumorigenesis, functioning through both inflammasome-dependent and independent mechanisms. Its influence on the host immune response is dual-faceted, exhibiting both promotive and inhibitory effects in the contexts of inflammation and tumors. These effects are predominantly contingent upon the specific cell type expressing AIM2 and the nature of the host's disease. This article seeks to review the latest advancements in understanding the cell-specific functions of AIM2 in inflammation and tumorigenesis, with the objective of offering insights for further research on AIM2 and informing the development of targeted therapeutic strategies for clinical application.

PANoptosis in autoimmune diseases interplay between apoptosis, necrosis, and pyroptosis

PANoptosis is a newly identified inflammatory programmed cell death (PCD) that involves the interplay of apoptosis, necrosis, and pyroptosis. However, its overall biological effects cannot be attributed to any one type of PCD alone. PANoptosis is regulated by a signaling cascade triggered by the recognition of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) by various sensors. This triggers the assembly of the PANoptosome, which integrates key components from other PCD pathways via adapters and ultimately activates downstream execution molecules, resulting in cell death with necrotic, apoptotic, and pyroptotic features. Autoimmune diseases are characterized by reduced immune tolerance to self-antigens, leading to abnormal immune responses, often accompanied by systemic chronic inflammation. Consequently, PANoptosis, as a unique innate immune-inflammatory PCD pathway, has significant pathophysiological relevance to inflammation and autoimmunity. However, most previous research on PANoptosis has focused on tumors and infectious diseases, leaving its activation and role in autoimmune diseases unclear. This review briefly outlines the characteristics of PANoptosis and summarizes several newly identified PANoptosome complexes, their activation mechanisms, and key components. We also explored the dual role of PANoptosis in diseases and potential therapeutic approaches targeting PANoptosis. Additionally, we review the existing evidence for PANoptosis in several autoimmune diseases and explore the potential regulatory mechanisms involved.

Impact of inflammasomes on the ocular surface

PURPOSE OF REVIEW

The ocular surface is prone to inflammation due to exposure to environmental irritants and pathogens. Inflammasomes are intracellular, multiprotein complexes that communicate potentially dangerous signals to the immune system. The identification of inflammasomes in various inflammatory ocular surface conditions can aid in the development of therapeutics to treat these chronic inflammatory conditions.

RECENT FINDINGS

Several inflammasomes have been associated with ocular surface disorders including dry eye disease, keratitis, and allergies. Mechanisms for activation of these inflammasomes with regards to specific disorders have been explored in models to aid in the development of targeted treatments.

SUMMARY

Research efforts continue to characterize the types of inflammasomes and activators of these in inflammatory ocular surface conditions. Various therapies targeting specific inflammasome types or pyroptosis are being tested preclinically to assess effects on decreasing the associated chronic inflammation.

Disrupted mitochondrial transcription factor A expression promotes mitochondrial dysfunction and enhances ocular surface inflammation by activating the absent in melanoma 2 inflammasome

PURPOSE

Severe dry eye disease causes ocular surface damage, which is highly associated with mitochondrial dysfunction. Mitochondrial transcription factor A (TFAM) is essential for packaging mitochondrial DNA (mtDNA) and is crucial for maintaining mitochondrial function. Herein, we aimed to explore the effect of a decreased TFAM expression on ocular surface damage.

METHODS

Female C57BL/6 mice were induced ocular surface injury by topical administrating benzalkonium chloride (BAC). Immortalized human corneal epithelial cells (HCECs) were stimulated by tert-butyl hydroperoxide (t-BHP) to create oxidative stress damage. HCECs with TFAM knockdown were established. RNA sequencing was employed to analyze the whole-genome expression. Mitochondrial changes were measured by transmission electron microscopy, Seahorse metabolic flux analysis, mitochondrial membrane potential, and mtDNA copy number. TFAM expression and inflammatory cytokines were determined using RT-qPCR, immunohistochemistry, immunofluorescence, and immunoblotting.

RESULTS

In both the corneas of BAC-treated mice and t-BHP-induced HCECs, we observed impaired TFAM expression, accompanied by mitochondrial structure and function defects. TFAM downregulation in HCECs suppressed mitochondrial respiratory capacity, reduced mtDNA content, induced mtDNA leakage into the cytoplasm, and led to inflammation. RNA sequencing revealed the absent in melanoma 2 (AIM2) inflammasome was activated in the corneas of BAC-treated mice. The AIM2 inflammasome activation was confirmed in TFAM knockdown HCECs. TFAM knockdown in t-BHP-stimulated HCECs aggravated mitochondrial dysfunction and the AIM2 inflammasome activation, thereby further triggering the secretion of inflammatory factors such as interleukin (IL) -1β and IL-18.

CONCLUSIONS

TFAM reduction impaired mitochondrial function, activated AIM2 inflammasome and promoted ocular surface inflammation, revealing an underlying molecular mechanism for ocular surface disorders.

The roles of AIM2 in neurodegenerative diseases: insights and therapeutic implications

AIM2, a cytosolic innate immune receptor, has the capability to recognize double-stranded DNA (dsDNA). This paper delineates the structural features of AIM2 and its mechanisms of activation, emphasizing its capacity to detect cytosolic DNA and initiate inflammasome assembly. Additionally, we explore the diverse functions of AIM2 in different cells. Insights into AIM2-mediated neuroinflammation provide a foundation for investigating novel therapeutic strategies targeting AIM2 signaling pathways. Furthermore, we present a comprehensive review of the roles of AIM2 in neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we discuss its therapeutic implications. In conclusion, a profound understanding of AIM2 in neurodegenerative diseases may facilitate the development of effective interventions to mitigate neuronal damage and slow disease progression.

IUPHAR ECR review: The cGAS-STING pathway: Novel functions beyond innate immune and emerging therapeutic opportunities

Stimulator of interferon genes (STING) is a crucial innate immune sensor responsible for distinguishing pathogens and cytosolic DNA, mediating innate immune signaling pathways to defend the host. Recent studies have revealed additional regulatory functions of STING beyond its innate immune-related activities, including the regulation of cellular metabolism, DNA repair, cellular senescence, autophagy and various cell deaths. These findings highlight the broader implications of STING in cellular physiology beyond its role in innate immunity. Currently, approximately 10 STING agonists have entered the clinical stage. Unlike inhibitors, which have a maximum inhibition limit, agonists have the potential for infinite amplification. STING signaling is a complex process that requires precise regulation of STING to ensure balanced immune responses and prevent detrimental autoinflammation. Recent research on the structural mechanism of STING autoinhibition and its negative regulation by adaptor protein complex 1 (AP-1) provides valuable insights into its different effects under physiological and pathological conditions, offering a new perspective for developing immune regulatory drugs. Herein, we present a comprehensive overview of the regulatory functions and molecular mechanisms of STING beyond innate immune regulation, along with updated details of its structural mechanisms. We discuss the implications of these complex regulations in various diseases, emphasizing the importance and feasibility of targeting the immunity-dependent or immunity-independent functions of STING. Moreover, we highlight the current trend in drug development and key points for clinical research, basic research, and translational research related to STING.