ASK1/2 signaling promotes inflammation in a mouse model of neutrophilic dermatosis.

Mice homozygous for the Tyr208Asn amino acid substitution in the carboxy terminus of Src homology region 2 (SH2) domain-containing phosphatase 1 (SHP-1) (referred to as Ptpn6spin mice) spontaneously develop a severe inflammatory disease resembling neutrophilic dermatosis in humans. Disease in Ptpn6spin mice is characterized by persistent footpad swelling and suppurative inflammation. Recently, in addition to IL-1α and IL-1R signaling, we demonstrated a pivotal role for several kinases such as SYK, RIPK1, and TAK1 in promoting inflammatory disease in Ptpn6spin mice. In order to identify new kinases involved in SHP-1-mediated inflammation, we took a genetic approach and discovered apoptosis signal-regulating kinases 1 and 2 (ASK1 and ASK2) as novel kinases regulating Ptpn6-mediated footpad inflammation. Double deletion of ASK1 and ASK2 abrogated cutaneous inflammatory disease in Ptpn6spin mice. This double deletion further rescued the splenomegaly and lymphomegaly caused by excessive neutrophil infiltration in Ptpn6spin mice. Mechanistically, ASK regulates Ptpn6spin-mediated disease by controlling proinflammatory signaling in the neutrophils. Collectively, the present study identifies SHP-1 and ASK signaling crosstalk as a critical regulator of IL-1α-driven inflammation and opens future avenues for finding novel drug targets to treat neutrophilic dermatosis in humans.

TAK1 restricts spontaneous NLRP3 activation and cell death to control myeloid proliferation.

The NOD-like receptor (NLR)-P3 inflammasome is a global sensor of infection and stress. Elevated NLRP3 activation levels are associated with human diseases, but the mechanisms controlling NLRP3 inflammasome activation are largely unknown. Here, we show that TGF-ß activated kinase-1 (TAK1) is a central regulator of NLRP3 inflammasome activation and spontaneous cell death. Absence of TAK1 in macrophages induced spontaneous activation of the NLRP3 inflammasome without requiring toll-like receptor (TLR) priming and subsequent activating signals, suggesting a distinctive role for TAK1 in maintaining NLRP3 inflammasome homeostasis. Autocrine tumor necrosis factor (TNF) signaling in the absence of TAK1 induced spontaneous RIPK1-dependent NLRP3 inflammasome activation and cell death. We further showed that TAK1 suppressed homeostatic NF-κB and extracellular signal-related kinase (ERK) activation to limit spontaneous TNF production. Moreover, the spontaneous inflammation resulting from TAK1-deficient macrophages drives myeloid proliferation in mice, and was rescued by RIPK1 deficiency. Overall, these studies identify a critical role for TAK1 in maintaining NLRP3 inflammasome quiescence and preserving cellular homeostasis and survival.