Calcium oxalate crystals induce renal inflammation by NLRP3-mediated IL-1β secretion

Nephrocalcinosis, acute calcium oxalate (CaOx) nephropathy, and renal stone disease can lead to inflammation and subsequent renal failure, but the underlying pathological mechanisms remain elusive. Other crystallopathies, such as gout, atherosclerosis, and asbestosis, trigger inflammation and tissue remodeling by inducing IL-1β secretion, leading us to hypothesize that CaOx crystals may induce inflammation in a similar manner. In mice, intrarenal CaOx deposition induced tubular damage, cytokine expression, neutrophil recruitment, and renal failure. We found that CaOx crystals activated murine renal DCs to secrete IL-1β through a pathway that included NLRP3, ASC, and caspase-1. Despite a similar amount of crystal deposits, intrarenal inflammation, tubular damage, and renal dysfunction were abrogated in mice deficient in MyD88; NLRP3, ASC, and caspase-1; IL-1R; or IL-18. Nephropathy was attenuated by DC depletion, ATP depletion, or therapeutic IL-1 antagonism. These data demonstrated that CaOx crystals trigger IL-1β–dependent innate immunity via the NLRP3/ASC/caspase-1 axis in intrarenal mononuclear phagocytes and directly damage tubular cells, leading to the release of the NLRP3 agonist ATP. Furthermore, these results suggest that IL-1β blockade may prevent renal damage in nephrocalcinosis

NLRP3 in Renal Injury and Inflammation

Renal cell injury, death and inflammation are hallmarks of chronic kidney disease (CKD). Unresolved inflammation can chronically damage renal tissue resulting in fibrosis and kidney failure. The Nlrp3 inflammasome has been implicated in the innate immune response to cellular injury and represents a potentially important pathway in the pathogenesis of CKD. The central hypothesis of this thesis is that NLRP3 plays a significant role in renal inflammation and chronic renal injury. In a mouse model of progressive renal injury and fibrosis (unilateral ureteral obstruction, UUO), Nlrp3 expression and inflammasome activation were increased in injured kidneys. Compared to wild-type counterparts, Nlrp3-/-mice undergoing UUO displayed reduced renal injury, fibrosis and inflammatory cytokine levels confirming an important role for Nlrp3 in experimental kidney disease. Bone marrow chimeras in the UUO model indicated that in addition to its inflammasome-forming capabilities in leukocytes, Nlrp3 may play a novel role in the renal epithelial compartment. Indeed, Nlrp3 expression was found in both human and mouse primary tubular epithelial cells. Unlike the inflammasome-forming capability of Nlrp3 in macrophages, renal tubular epithelial cells lacked the components of the inflammasome including caspase-1 and its substrate IL-1β. Rather, Nlrp3 primarily regulated caspase-8 activation and apoptosis in these cells. Experiments to elucidate the mechanism of Nlrp3- regulated caspase-8 activation and apoptosis suggested the involvement of Asc, but not inflammatory cytokines, caspase-1 or caspase-11. Furthermore, Nlrp3-/- tubular epithelial cells were found to have impaired mitochondrial ROS production that was linked to decreased caspase-8 activation during apoptosis. Taken together, results from this thesis identify a significant and multidimensional role for Nlrp3 in the pathogenesis of kidney disease. First, Nlrp3 inflammasome activation in macrophages releases cytokines such as IL-1β and IL-18 that cause renal inflammation, fibrosis and tubular epithelial cell apoptosis. Second, Nlrp3 expressed in tubular epithelial cells displays an intrinsic inflammasome-independent function to regulate caspase-8, mitochondrial ROS and apoptosis. These data identify Nlrp3 as an important player in renal injury and potential therapeutic target for CKD

The NLRP3 Inflammasome Promotes Renal Inflammation and Contributes to CKD

Inflammation significantly contributes to the progression of chronic kidney disease (CKD). Inflammasome-dependent cytokines, such as IL-1β and IL-18, play a role in CKD, but their regulation during renal injury is unknown. Here, we analyzed the processing of caspase-1, IL-1β, and IL-18 after unilateral ureteral obstruction (UUO) in mice, which suggested activation of the Nlrp3 inflammasome during renal injury. Compared with wild-type mice, Nlrp3−/− mice had less tubular injury, inflammation, and fibrosis after UUO, associated with a reduction in caspase-1 activation and maturation of IL-1β and IL-18; these data confirm that the Nlrp3 inflammasome upregulates these cytokines in the kidney during injury. Bone marrow chimeras revealed that Nlrp3 mediates the injurious/inflammatory processes in both hematopoietic and nonhematopoietic cellular compartments. In tissue from human renal biopsies, a wide variety of nondiabetic kidney diseases exhibited increased expression of NLRP3 mRNA, which correlated with renal function. Taken together, these results strongly support a role for NLRP3 in renal injury and identify the inflammasome as a possible therapeutic target in the treatment of patients with progressive CKD

Alum interaction with dendritic cell membrane lipids is essential for its adjuvanticity.

As an approved vaccine adjuvant for use in humans, alum has vast health implications, but, as it is a crystal, questions remain regarding its mechanism. Furthermore, little is known about the target cells, receptors, and signaling pathways engaged by alum. Here we report that, independent of inflammasome and membrane proteins, alum binds dendritic cell (DC) plasma membrane lipids with substantial force. Subsequent lipid sorting activates an abortive phagocytic response that leads to antigen uptake. Such activated DCs, without further association with alum, show high affinity and stable binding with CD4(+) T cells via the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1). We propose that alum triggers DC responses by altering membrane lipid structures. This study therefore suggests an unexpected mechanism for how this crystalline structure interacts with the immune system and how the DC plasma membrane may behave as a general sensor for solid structures