Maternally contributed Nlrp9b expressed in human and mouse ovarian follicles contributes to early murine preimplantation development

NLRP inflammasomes in health and disease

NLRP inflammasomes are a group of cytosolic multiprotein oligomer pattern recognition receptors (PRRs) involved in the recognition of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) produced by infected cells. They regulate innate immunity by triggering a protective inflammatory response. However, despite their protective role, aberrant NLPR inflammasome activation and gain-of-function mutations in NLRP sensor proteins are involved in occurrence and enhancement of non-communicating autoimmune, auto-inflammatory, and neurodegenerative diseases. In the last few years, significant advances have been achieved in the understanding of the NLRP inflammasome physiological functions and their molecular mechanisms of activation, as well as therapeutics that target NLRP inflammasome activity in inflammatory diseases. Here, we provide the latest research progress on NLRP inflammasomes, including NLRP1, CARD8, NLRP3, NLRP6, NLRP7, NLRP2, NLRP9, NLRP10, and NLRP12 regarding their structural and assembling features, signaling transduction and molecular activation mechanisms. Importantly, we highlight the mechanisms associated with NLRP inflammasome dysregulation involved in numerous human auto-inflammatory, autoimmune, and neurodegenerative diseases. Overall, we summarize the latest discoveries in NLRP biology, their forming inflammasomes, and their role in health and diseases, and provide therapeutic strategies and perspectives for future studies about NLRP inflammasomes.

The NLR gene family: from discovery to present day

The mammalian NLR gene family was first reported over 20 years ago, although several genes that were later grouped into the family were already known at that time. Although it is widely known that NLRs include inflammasome receptors and/or sensors that promote the maturation of caspase 1, IL-1β, IL-18 and gasdermin D to drive inflammation and cell death, the other functions of NLR family members are less well appreciated by the scientific community. Examples include MHC class II transactivator (CIITA), a master transcriptional activator of MHC class II genes, which was the first mammalian NBD-LRR-containing protein to be identified, and NLRC5, which regulates the expression of MHC class I genes. Other NLRs govern key inflammatory signalling pathways or interferon responses, and several NLR family members serve as negative regulators of innate immune responses. Multiple NLRs regulate the balance of cell death, cell survival, autophagy, mitophagy and even cellular metabolism. Perhaps the least discussed group of NLRs are those with functions in the mammalian reproductive system. The focus of this Review is to provide a synopsis of the NLR family, including both the intensively studied and the underappreciated members. We focus on the function, structure and disease relevance of NLRs and highlight issues that have received less attention in the NLR field. We hope this may serve as an impetus for future research on the conventional and non-conventional roles of NLRs within and beyond the immune system.

NLRP9 involved in antiviral innate immunity via binding VIM in IPEC-J2 cells

BACKGROUND

Nucleotide-binding oligomerization domain (NOD)-like receptors with a pyrin domain (PYD)-containing protein 9 (NLRP9) was the first nucleotide-binding region receptor (NLR) proposed to be expressed and function only in the reproductive system. Recent evidence suggests that NLRP9 is also capable of playing a role in infectious and inflammatory diseases.

RESULTS AND CONCLUSIONS

In this study, we examined the expression of NLRP9 in various tissues of piglets and IPEC-J2 cells. The results showed that high expression of NLRP9 mRNA and protein were detected in both intestine of piglets and IPEC-J2 cells. Both LPS and poly I:C significantly up-regulated NLRP9 protein levels in the IPEC-J2 cells. Besides, poly I:C upregulated the level of transcriptional elements NF-κB, IRF3, IRF7, ISG15, ISG56, OAS1, and IFNB1. Furthermore, interference with the NLRP9 gene in the presence of poly I:C strongly downregulated the expression of all the above genes. Moreover, we demonstrated for the first time that NLRP9 acts in combination with VIM (Vimentin). These results suggested that NLRP9 may participate in the antiviral innate immune by binding to VIM in the porcine intestine. The findings provide preliminary insights into the molecular mechanisms involved in the regulation of mucosal immunity in the porcine intestine by NLRP9.

Inflammasomes as regulators of non-infectious disease

Inflammasomes are cytoplasmic organelles that stimulate inflammation upon cellular detection of infectious or non-infectious stress. While much foundational work has focused on the infection-associated aspects of inflammasome activities, recent studies have highlighted the role of inflammasomes in non-infectious cellular and organismal functions. Herein, we discuss the evolution of inflammasome components and highlight characteristics that permit inflammasome regulation of physiologic processes. We focus on emerging data that highlight the importance of inflammasome proteins in the regulation of reproduction, development, and malignancy. A framework is proposed to contextualize these findings.

In silico analysis and molecular docking studies of natural compounds of Withania somnifera against bovine NLRP9

CONTEXT

NLRP9 is a member of nucleotide-binding domain leucine-rich repeat-containing receptors and is found to be associated with many inflammatory diseases. In the current scenario, the identification of promising anti-inflammatory compounds from natural sources by repurposing approach is still relevant for the early prevention and effective management of the disease.

METHODS

In the present study, we docked bioactives of Ashwagandha (Withanoside IV, Withanoside V, Withanolide A, Withanolide B, and Sitoindoside IX) and two control drugs against bovine NLRP9 protein. ADME/T analysis was used to determine the physiochemical properties of compounds and standard drugs. Molecular modeling was used to evaluate the correctness and quality of protein structures. In silico docking analysis revealed Withanolide B had the highest binding affinity score of -10.5 kcal/mol, whereas, among control drugs, doxycycline hydrochloride was most effective (-10.3 kcal/mol). The results of this study revealed that bioactives of Withania somnifera could be promising inhibitors against bovine NLRP9. In the present study, molecular simulation was used to measure protein conformational changes over time. The Rg value was found to be 34.77A°. RMSD and B-factor were also estimated to provide insights into the flexibility and mobile regions of protein structure. A functional protein network interaction was constructed from information collected from non-curative sources as protein-protein interactions (PPI) that play an important role in determining the function of the target protein and the ability of the drug molecule. Thus, in the present situation, it is important to identify bioactives with the potential to combat inflammatory diseases and provide strength and immunity to the host. However, there is still a need to study in vitro and in vivo to further support these findings.

NLRP9 in innate immunity and inflammation

The nucleotide-binding domain leucine-rich repeat containing receptors (NLRs) are a family of evolutionarily conserved proteins. Several members of NLRs, notably NLRP1, NLRP3 and NLRC4, are able to form cytosolic oligomeric signalling platforms termed inflammasomes to mediate immune response towards pathogens, damage and stress. However, the functions of many NLRs still remain elusive. In the past few years, a couple of less-characterized NLR members are emerging as important signalling molecules with fundamental functions in host defence and inflammation. Among them, NLRP9 is an NLR originally proposed to be expressed and function solely in the reproductive system. Recent evidence has suggested that NLRP9 is also capable of initiating inflammasome formation in the intestine to restrict replication and damage brought by rotavirus infection. Here, we highlight the latest progress in characterization of the role of NLRP9 in infectious and inflammatory diseases, as well as the newest crystallographic and biochemical studies on NLRP9. Finally, we discuss some important questions remained to be answered regarding the molecular and cellular mechanisms governing NLRP9's function in innate immunity and inflammation.