Background:

Inflammasomes are multiprotein complexes of pattern recognition receptors (PRRs) recognized as key triggers of cellular injury. TLRs provide the first signal for induction of the Nlrp3 inflammasome by inducing expression of Nlrp3 and its substrates. A second signal is needed for formation of the mature inflammasome, resulting in recruitment of an adapter protein, ASC, and the protease pro-caspase-1, which oligomerizes with Nlrp3 to form the mature inflammasome. Our laboratory has shown blockade of this inflammasome protects from ischemic renal injury. This study evaluated the role of individual Nlrp3 inflammasome components to renal cell death.

Methods:

Primary RTE cells from WT, TLR2-/-, Nlrp3-/-, ASC-/- and Caspase 1-/- mice were isolated, grown to near confluency, treated with ultrapure TLR2 and Nlrp3 ligands and analyzed for inflammasome components and markers of cellular death. After stimulation, supernatant was collected, precipitated for total protein and LDH and HMGB1 measured. WT RTE cell pellets were collected for qPCR to assess the expression of inflammasome components.

Results:

There was similar expression of all three inflammasome components in resting RTE cells, but upon stimulation with the TLR2 ligand Pam(3)CysSK(4), Nlrp3 and IL-1b, but not ASC or pro-caspase 1, were highly upregulated in the primary RTE cells from WT mice (data not shown). The absence of any of the individual inflammasome components was highly protective from cell death induced by the TLR2 ligand (Pam3, signal 1) plus the Nlrp3 ligand (ATP, signal 2) in the primary RTEs from WT mice; as indicated by LDH and HMGB1 released into the supernatant (Figure 1A and B, respectfully).

Conclusions:

The absence of the inflammasome components Nlrp3, ASC and pro-caspase-1 protects from DAMP-induced cell death in primary RTEs, suggesting the Nlrp3 inflammasome is a key intracellular target in renal tubular injury under conditions of sterile inflammation. Our laboratory is further investigating the signaling pathways induced in RTE cells that contribute to cell death associated with engagement of the ligands of this inflammasome.

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