NOD-Like Receptors in Infection, Immunity, and Diseases

Nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs) are pattern-recognition receptors similar to toll-like receptors (TLRs). While TLRs are transmembrane receptors, NLRs are cytoplasmic receptors that play a crucial role in the innate immune response by recognizing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Based on their N-terminal domain, NLRs are divided into four subfamilies: NLRA, NLRB, NLRC, and NLRP. NLRs can also be divided into four broad functional categories: inflammasome assembly, signaling transduction, transcription activation, and autophagy. In addition to recognizing PAMPs and DAMPs, NLRs act as a key regulator of apoptosis and early development. Therefore, there are significant associations between NLRs and various diseases related to infection and immunity. NLR studies have recently begun to unveil the roles of NLRs in diseases such as gout, cryopyrin-associated periodic fever syndromes, and Crohn's disease. As these new associations between NRLs and diseases may improve our understanding of disease pathogenesis and lead to new approaches for the prevention and treatment of such diseases, NLRs are becoming increasingly relevant to clinicians. In this review, we provide a concise overview of NLRs and their role in infection, immunity, and disease, particularly from clinical perspectives.

Papel das proteínas Nod na modulação da resposta imune nas doenças periodontais / Role of Nod proteins in the modulation of the immune response in periodontal diseases

As interações microrganismo-hospedeiro se iniciam pela detecção de padrões moleculares associados a microrganismos (MAMPs) por receptores semelhantes à Toll (TLR) e por proteínas com domínio de ligação à nucleotídeos e oligomerização (Nod) na resposta imune inata. No entanto, como a cavidade bucal saudável é continuamente colonizada por microrganismos não patogênicos que também apresentam MAMPs, deve haver um mecanismo endógeno de regulação negativa da resposta do hospedeiro para evitar uma resposta exagerada e desnecessária com consequências negativas ao hospedeiro. Os mecanismos associados à distinção de microrganismos comensais e patogênicos na mucosa bucal são ainda pouco compreendidos. As proteínas Nod foram inicialmente descritas como 'TLRs intracelulares' capazes de reconhecer MAMPs no citosol; no entanto, estudos in vitro indicam que Nod têm papel relevante na regulação da expressão de RANKL e OPG induzidas por antígenos microbianos, bem como na modulação da atividade de vias de sinalização intracelular associadas à expressão de citocinas diretamente relacionadas à regulação do turnover do tecido ósseo. Devido à escassez de informações sobre o papel das proteínas Nod na modulação das interações microrganismo-hospedeiro na mucosa oral e com base nestas informações, nossa hipótese é que as proteínas Nod tem um papel relevante na modulação da reação inflamatória e suas consequências, incluindo a reabsorção do osso alveolar. Para testar esta hipótese, os objetivos específicos propostos foram: avaliar em camundongos knockout para Nod1, Nod2 ou Rip2, através de microtomografia computadorizada e avaliações histológicas descritivas, estereométricas e imunohistoquímicas (TRAP), o papel das proteínas Nod na inflamação e reabsorção óssea associadas à doença periodontal experimental induzida por bactérias inativadas por calor. A influência das proteínas Nod nas redes de citocinas e na sinalização intracelular associadas com a doença periodontal foi determinada in vitro em culturas primárias de macrófagos através de ensaios baseados nas plataformas ELISA e PCR em tempo real. Nossos resultados mostraram que, enquanto que nos camundongos Nod1 KO a reabsorção óssea alveolar e o número de osteoclastos aumentou significantemente, a deleção de Nod2 causou efeito contrário, diminuindo a reabsorção óssea. Os resultados in vitro foram correspondentes com os dados in vivo no caso de Nod2 (qPCR array, ELISA citocinas e vias de sinalização) e distintos no caso Nod1 (ELISA citocinas e vias de sinalização). Estes resultados demonstram que as proteínas Nod tem papel relevante na modulação das interações bactéria-hospedeiro associadas à doença periodontal induzida por bactérias inativadas por calor. Enquanto Nod1 parece exercer papel protetor na inflamação e reabsorção óssea, Nod2 atua como amplificador da resposta do hospedeiro

Recognition of pathogenic bacteria by the host is initially mediated by the innate immune response through detection of microbe-associated molecular pattern (MAMPs) by Toll-like receptors (TLR) and Nucleotide-oligomerization domain (Nod) proteins. Since the oral cavity, as well as other mucosal surfaces, is continuously colonized with non-pathogenic bacteria that also present MAMPs, there has to be an endogenous negative regulatory mechanism in place to prevent an overt host response with deleterious consequences. Specifically in the oral mucosa, it is not clear how the immune system is able to quickly distinguish between commensal and pathogenic bacteria and tailor the host response. Nod proteins were initially described as 'intracellular TLRs' that recognize MAMPs associated with bacteria invading the cytosol; however these proteins have been shown to modulate the activation of various signaling pathways involved in the expression of inflammatory genes, including MAPK and NF-κB in concert with TLR stimulation. There is paucity of information on the in vivo role of Nod proteins in the modulation of host-microbe interactions in the oral mucosa. Based on this information, our hypothesis is that Nod proteins play an important role in the modulation of the inflammatory reaction associated with periodontal diseases and its consequences, including alveolar bone resorption. To test this hypothesis, we propose the following specific aims: Assess the role of Nod proteins in the inflammation and bone resorption in experimentally-induced periodontal disease. Describe the influence of Nod proteins on the cytokine and signaling networks associated with periodontal disease

Regulation of NOD like receptors and inflammasome during the inflammation / 生理学报

The innate immune system plays a crucial role in the rapid recognition and elimination of invading microbes. Detection of microbes relies on germ-line encoded pattern recognition receptors (PRRs) that recognize essential bacterial molecules, so-called pathogen-associated molecular patterns (PAMPs). A subset of PRRs, belonging to the nucleotide binding oligomerization domain (NOD)-like receptor (NLR) families, detects viral and bacterial pathogens in the cytosol of host cells and induces the assembly of a multi-protein signaling platform called the inflammasome. The inflammasome serves as an activation platform for the cysteine protease Caspase-1, a central mediator of innate immunity. Caspase-1 initiates a novel form of cell death called pyroptosis. Inflammasome activation by pathogen-associated signatures results in the autocatalytic cleavage of Caspase-1 and ultimately leads to the processing and thus secretion of pro-inflammatory cytokines, most importantly interleukin (IL)-1β and IL-18. Here, we review the recent advancements of negative regulatory functions and mechanisms leading to the activation of NLRP1, NLRP3, NLRC4, and AIM2 inflammasomes.

Receptores tipo Toll, patogénesis y respuesta inmune a Helicobacter pylori / Toll-like receptors, pathogenesis and immune response to Helicobacter pylori

Helicobacter pylori coloniza el epitelio gástrico y la mayoría de las personas infectadas es asintomática, de 10 al 20 por ciento desarrolla gastritis atrófica, úlcera péptica, y menos de 3 por ciento genera cáncer gástrico. Estas patologías están determinadas por la relación entre los factores de virulencia de la bacteria y los factores del hospedero como predisposición genética y respuesta inmune. La inmunidad innata, representada principalmente por los receptores tipo Toll y tipo Nod, reconocen a sus ligandos específicos y activan factores de transcripción como NF-kB, AP-1, CREB-1, induciendo la producción de citocinas inflamatorias como IL-8, IL-12, IL-6, IL-1β, IL-18 y TNF-α, e IL-10. La inflamación crónica favorece los cambios de morfología gástrica, evita la apoptosis y favorece la angiogénesis, ocasionando lesiones neoplásicas y cáncer. El objetivo de esta revisión es analizar los mecanismos propuestos a la fecha de la respuesta inmune innata y adaptativa, involucrados en la infección por H. pylori, y se puntualiza en los mecanismos de eliminación o persistencia de la infección.

Helicobacter pylori colonize the gastric epithelial, most infected people are asymptomatic, 10 to 20 percent develop atrophic gastritis, peptic ulcer and less than 3 percent gastric cancer. These diseases are determined by the relationship between virulence factors of bacteria, host factors such as, genetic predisposition, and immune response. The innate immune response mainly represented by Toll-like receptors and Nod-like receptors that recognize their specific ligands, activate transcription factors as NF-kB, AP-1, CREB-1, inducing production of inflammatory cytokines such as IL -8, IL-12, IL-6, IL-1β, IL-18, TNF-α and IL-10. Chronic inflammation promotes gastric morphological changes, prevents apoptosis and allows angiogenesis generating neoplasic lesions and cancer. The aim of this review is to analyze the mechanisms proposed to date of the innate and adaptative immune response involved in H. pylori infection; remarking the mechanisms related in the elimination or persistence.

Papel das proteínas intracelulares nod e da proteína adaptadora myD88 na regulação de espressão de RANKL e modulação da resposta inflamatória induzidos por antígenos bacterianos in vitro: estudo em células relevantes de periodonto / Role of nod an myD88 proteins on the regulation of bacterial antigen-induced expression of RANKL and on the modulation of inflammation: a study on relevant cells of the periodontium

A reabsorcao do osso alveolar e uma das principais caracteristicas associadas a progressao da doenca periodontal. Apesar da enorme complexidade da microbiota envolvida, considera-se que bacterias Gram-negativas tenham um papel relevante em sua etiopatogenese. Um dos fatores de virulencia destes microrganismos e representado por um componente de sua parede externa denominado lipopolissacarideo (LPS). A presenca de LPS na proximidade dos tecidos periodontais e capaz de induzir a producao de diversos mediadores inflamatorios que levam a degradacao tanto do tecido conjuntivo quanto osseo. Atualmente acredita-se que a interacao do ligante do receptor-ativador do fator nuclear kappa-B (RANKL) com seu receptor (RANK) presente em precursores hematopoieticos e necessaria e suficiente para a inducao da diferenciacao de osteoclastos. Por outro lado, a ligacao de RANKL com seu falso-receptor, denominado osteoprotegerina (OPG), reduz sua biodisponibilidade e inibe, desta forma, a osteoclastogenese. Assim, a razao da expressao de RANKL e OPG e considerada como o principal determinante do “turnover” do tecido osseo. A producao de RANKL e OPG depende das vias de sinalizacao ativadas, as quais sao influenciadas pela natureza do estimulo extracelular. Atualmente, a familia de receptores NLRs (nod-like receptors) foi identificada como receptor intracelular para componentes bacterianos e agentes moduladores de diferentes vias de sinalizacao. Considerando a relevancia do LPS bacteriano na patogenese da doenca periodontal, o papel do RANKL no processo de reabsorcao ossea e a possivel implicacao das proteinas Nod na transducao de sinais regulando a expressao de RANKL, o objetivo geral deste projeto foi estudar os mecanismos de regulacao da expressao de RANKL induzido por LPS bacteriano em celulas relevantes do periodonto (macrofagos, osteoblastos e fibroblastos). Os objetivos especificos propostos...

Bone resorption is one of the major characteristics of destructive periodontal disease. Despite the great number of different bacterial species in the dental biofilm, Gramnegative microorganisms were demonstrated to have a very important role on periodontal disease pathogenesis. Lipopolysaccharide (LPS) is a bacterial cell wall component, which is acknowledged as one of the main virulence factors of these microorganisms. The mere presence of LPS in proximity with the periodontal tissues initiates the expression and production of inflammatory mediators and other cytokines which can culminate in degradation of both soft and hard tissues. It is currently accepted that the interaction between receptor-activator of nuclear factor kappa-B ligand (RANKL) and its receptor (RANK) is both necessary and sufficient to induce osteoclast differentiation and activation. However, RANKL can interact with its soluble decoy receptor osteoprotegerin (OPG) inhibiting osteoclastogenesis by decreasing the bioavailability of RANKL. Production of RANKL/OPG is the result of the signaling pathways activated by external stimuli. Recently, the NLR (nod-like receptors) family was identified as cytosolic receptors for bacterial components and also, as capable of modulating different signaling pathways. Considering the relevance of LPS and RANKL in bone resorption and the possible implication of Nod proteins in signal transduction regulating RANKL expression, the aim of this study was to evaluate the influence of different intracellular signaling pathways on the regulation of RANKL expression induced by LPS in relevant cells of the periodontium (macrophages, osteoblasts and fibroblasts). The specific objectives proposed were to determine after LPS and interleukin-1 beta stimulation the role of MyD88-dependent and independent signaling pathways, Nod1 and Nod2 on the expression of RANKL, OPG, IL-10 and IFN-beta...