RESUMO
Hemolysis causes an increase of intravascular heme, oxidative damage, and inflammation in which macrophages play a critical role. In these cells, heme can act as a prototypical damage-associated molecular pattern, inducing TLR4-dependent cytokine production through the MyD88 pathway, independently of TRIF. Heme promotes reactive oxygen species (ROS) generation independently of TLR4. ROS and TNF production contribute to heme-induced necroptosis and inflammasome activation; however, the role of ROS in proinflammatory signaling and cytokine production remains unknown. In this study, we demonstrate that heme activates at least three signaling pathways that contribute to a robust MAPK phosphorylation and cytokine expression in mouse macrophages. Although heme did not induce a detectable Myddosome formation, the TLR4/MyD88 axis was important for phosphorylation of p38 and secretion of cytokines. ROS generation and spleen tyrosine kinase (Syk) activation induced by heme were critical for most proinflammatory signaling pathways, as the antioxidant N-acetyl-l-cysteine and a Syk inhibitor differentially blocked heme-induced ROS, MAPK phosphorylation, and cytokine production in macrophages. Early generated mitochondrial ROS induced by heme was Syk dependent, selectively promoted the phosphorylation of ERK1/2 without affecting JNK or p38, and contributed to CXCL1 and TNF production. Finally, lethality caused by sterile hemolysis in mice required TLR4, TNFR1, and mitochondrial ROS, supporting the rationale to target these pathways to mitigate tissue damage of hemolytic disorders.
Assuntos
Heme/metabolismo , Hemólise/imunologia , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais/imunologia , Animais , Quimiocina CXCL1/metabolismo , Modelos Animais de Doenças , Humanos , Macrófagos/citologia , Macrófagos/imunologia , Camundongos , Camundongos Knockout , Mitocôndrias/imunologia , Mitocôndrias/metabolismo , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Fosforilação/imunologia , Receptores Tipo I de Fatores de Necrose Tumoral/genética , Receptores Tipo I de Fatores de Necrose Tumoral/metabolismo , Quinase Syk/metabolismo , Receptor 4 Toll-Like/genética , Receptor 4 Toll-Like/metabolismo , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Critical to the design and assessment of interventions for enteropathy and its developmental consequences in children living in impoverished conditions are non-invasive biomarkers that can detect intestinal damage and predict its effects on growth and development. We therefore assessed fecal, urinary and systemic biomarkers of enteropathy and growth predictors in 375 6-26 month-old children with varying degrees of malnutrition (stunting or wasting) in Northeast Brazil. 301 of these children returned for followup anthropometry after 2-6m. Biomarkers that correlated with stunting included plasma IgA anti-LPS and anti-FliC, zonulin (if >12m old), and intestinal FABP (I-FABP, suggesting prior barrier disruption); and with citrulline, tryptophan and with lower serum amyloid A (SAA) (suggesting impaired defenses). In contrast, subsequent growth was predicted in those with higher fecal MPO or A1AT and also by higher L/M, plasma LPS, I-FABP and SAA (showing intestinal barrier disruption and inflammation). Better growth was predicted in girls with higher plasma citrulline and in boys with higher plasma tryptophan. Interactions were also seen with fecal MPO and neopterin in predicting subsequent growth impairment. Biomarkers clustered into markers of 1) functional intestinal barrier disruption and translocation, 2) structural intestinal barrier disruption and inflammation and 3) systemic inflammation. Principle components pathway analyses also showed that L/M with %L, I-FABP and MPO associate with impaired growth, while also (like MPO) associating with a systemic inflammation cluster of kynurenine, LBP, sCD14, SAA and K/T. Systemic evidence of LPS translocation associated with stunting, while markers of barrier disruption or repair (A1AT and Reg1 with low zonulin) associated with fecal MPO and neopterin. We conclude that key noninvasive biomarkers of intestinal barrier disruption, LPS translocation and of intestinal and systemic inflammation can help elucidate how we recognize, understand, and assess effective interventions for enteropathy and its growth and developmental consequences in children in impoverished settings.