AKI is associated with a high incidence of cell death and the production of cellular debris. The most prominent cause of acute renal damage is acute tubular necrosis (ATN). ATN is linked to an inflammatory response comprising monocytes/macrophages and neutrophil infiltration, which exacerbates the kidney damage
[12][13]. The evidence for the inflammasome’s function in acute renal disease is compelling. Deficiency of the inflammasome component, caspase-1, in animals provides resistance against AKI in several models such as cisplatin and ischemia-induced acute renal failure
[14][15][16][17]. Moreover, inhibition of nucleotide-binding domain-like receptor family pyrin domain containing 3 (NLRP3) by hydroxychloroquine decreased NF-κB signalling, as well as cathepsin-B and L activities, and protected rodents from AKI
[18]. The extracellular matrix (ECM) components biglycan and hyaluronan, as well as ATP acting via P2X7 receptors, activated the NLRP3 inflammasome
[19][20]. The pathogenic roles of the NLRP3 inflammasome have been demonstrated in ischemia-reperfusion injury (IRI)
[18][21][22][23], folic acid-induced AKI
[24], rhabdomyolysis-induced kidney injury
[25], and contrast-induced kidney injury
[26]. During contrast-induced AKI, canonical NLRP3 inflammasome activation in local and migratory macrophages led to elevated IL-1β levels in mice, whereas
Nlrp3-/- animals were protected
[26]. Infection-induced AKI models have also been shown to activate canonical inflammasomes. In a caecal ligation puncture model (sepsis-induced AKI), NLRP3 deficiency and caspase-1 suppression reduced kidney injury, inflammation, and caspase-1 activation
[27]. Furthermore, mice with caspase-1 deficiency were protected from endotoxemic AKI, hypotension, and mortality caused by LPS
[28]. Neutralization of IL-1β and IL-18, on the other hand, was unable to reverse LPS-induced AKI, implying that the non-canonical inflammasome and pyroptosis play an important role
[29]. Accordingly, the induction of pyroptosis has been related to caspase 11 upregulation, the non-canonical pyroptosis pathway, demonstrated in renal proximal tubular cells treated with LPS. The authors suggest that pyroptosis induction could be an early event in septic models
[30]. Furthermore, Astragaloside-IV protected from cisplatin-induced AKI by promoting autophagy and inhibiting NF-kB signalling, thus lowering the expression of inflammasome components
[31]. Interestingly, NLRP1 activation was elevated in cisplatin-induced AKI, likely upstream of caspase-1 activation
[32]. In this model, the deletion of caspase 11 promotes the downregulation of IL-18 urine secretion, decreasing tubular damage, immune macrophage, and neutrophil infiltration, and attenuating renal dysfunction. On the other way, caspase 11 upregulation induces the cleavage of gasdermin D into gasdemin N to trigger pyroptosis
[33]. In addition, the deletion of GASMDE, a member of the GASDM family, decreases cisplatin-induced damage by blocking pyroptosis and IL-1β release
[34]. During the pathogenesis of uric acid-induced nephropathy, uric acid crystals activate the NLRP3 inflammasome, suggesting a novel pathomechanism of crystalline nephropathy
[35]. The NLRP3 inflammasome complex must be activated for renal IL-17A to be produced, which is an essential proinflammatory cytokine in AKI
[36]. The discovery of the underlying mechanisms could assist the therapeutic suppression of IL-17A in AKI. Further, Deplano et al. reported that P2X7R (P2X purinoceptor) deficiency in rats reduced the activation of NLRP3-inflammasome in macrophages, and also crescentic glomerular damage in experimental nephrotoxic nephritis coupled with crescentic glomerulonephritis
[37]. Together, these data suggest that inflammasome components are promising therapeutic targets for treatment of AKI.
Several of the signalling molecules involved in regulating programmed cell death also modulate inflammasome activation in a cell-intrinsic manner. Necroptosis is typically seen as a back-up that kicks in when apoptosis is prevented; pyroptosis is a fundamental cellular mechanism triggered by the inflammasome in response to a wide spectrum of Pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs)
[38]. Activation of inflammatory caspases such as caspase-1, caspase-4, caspase-5, and caspase-11 leads to pyroptosis, which relies on gasdermin-D to produce plasma membrane pores
[39]. Due to their limited potential to release IL-1β, the prevalence of pyroptosis in tubular epithelial cells (TECs) has been disputed
[40]. Pyroptosis, characterised by elevated caspase-1 activation and IL-1β production, has been proposed to emerge in kidney tubular cells during renal IRI
[41].
Mice lacking distinct inflammasome components were utilised to establish the inflammasome’s participation in several experimental models of renal damage, but the specific role of intrinsic renal cells in inflammasome activation remains unknown
[42]. Some studies stated that TEC apoptosis and pyroptosis are the key drivers of contrast-induced AKI
[43][44], others did not show TEC apoptosis
[26][45], canonical inflammasome formation in TECs, or IL-1β release from TECs in response to contrast-induced AKI
[26][46]. Necroptosis mediated NLRP3 inflammasome plays a key role in the pathogenesis of lupus nephritis
[47] as well as the transition from AKI to CKD
[48]. Emerging evidence indicates that several signalling mechanisms that had been assumed to be biochemically independent for a long time communicate with one another. Nevertheless, the impact of apoptotic and regulated necrosis signalling molecules on the inflammasome is inconsistent and depends on the cell type and cellular environment. As a result, it is still a long way from understanding how these chemicals lead to altered inflammasome expression across various settings, as well as why these cell death mechanisms have developed to participate in inflammasome activation.