Background The genetic determinants of the human innate immune response are poorly understood. Apolipoprotein (Apo) E, a lipid-trafficking protein that affects inflammation, has well-described ...wild-type (ε3) and disease-associated (ε2 and ε4) alleles, but its connection to human innate immunity is undefined. Objective We sought to define the relationship of APOε4 to the human innate immune response. Methods We evaluated APOε4 in several functional models of the human innate immune response, including intravenous LPS challenge in human subjects, and assessed APOε4 association to organ injury in patients with severe sepsis, a disease driven by dysregulated innate immunity. Results Whole blood from healthy APOε3 / APOε4 volunteers induced higher cytokine levels on ex vivo stimulation with Toll-like receptor (TLR) 2, TLR4, or TLR5 ligands than blood from APOε3 / APOε3 patients, whereas TLR7/8 responses were similar. This was associated with increased lipid rafts in APOε3/APOε4 monocytes. By contrast, APOε3 / APOε3 and APOε3 / APOε4 serum neutralized LPS equivalently and supported similar LPS responses in Apoe -deficient macrophages, arguing against a differential role for secretory APOE4 protein. After intravenous LPS, APOε3/APOε4 patients had higher hyperthermia and plasma TNF-α levels and earlier plasma IL-6 than APOε3/APOε3 patients. APOE4-targeted replacement mice displayed enhanced hypothermia, plasma cytokines, and hepatic injury and altered splenic lymphocyte apoptosis after systemic LPS compared with APOE3 counterparts. In a cohort of 828 patients with severe sepsis, APOε4 was associated with increased coagulation system failure among European American patients. Conclusions APOε4 is a determinant of the human innate immune response to multiple TLR ligands and associates with altered patterns of organ injury in human sepsis.
Abstract Background Assembly of fibronectin matrices is associated with integrin receptor turnover and is an important determinant of tissue remodeling. Although it is well established that ...fibronectin is the primary ligand for α5β1 receptor, the relationship between fibronectin matrix assembly and the fate of internalized α5 integrin remains poorly characterized. Materials and methods To evaluate the effect of fibronectin matrix on the fate of internalized α5 integrin, fibronectin-null Chinese hamster ovary and mouse embryo fibroblast cells were used to track the fate of α5 after exposure to exogenous fibronectin. Results In the absence of matrix-capable fibronectin dimer, levels of internalized α5 decreased rapidly over time. This correlated with a decline in total cellular α5 and was associated with the ubiquitination of α5 integrin. In contrast, internalized and total cellular α5 protein levels were maintained when matrix-capable fibronectin was present in the extracellular space. Further, we show that ubiquitination and degradation of internalized α5 integrin in the absence of fibronectin require the presence of two specific lysine residues in the α5 cytoplasmic tail. Conclusions Our data demonstrate that α5 integrin turnover is dependent on fibronectin matrix assembly, where the absence of matrix-capable fibronectin in the extracellular space targets the internalized receptor for rapid degradation. These findings have important implications for understanding tissue-remodeling processes found in wound repair and tumor invasion.
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