Sirt1 negatively regulates FcεRI-mediated mast cell activation through AMPK- and PTP1B-dependent processes

Abstract

Sirt1, a key regulator of metabolism and longevity, has recently been implicated in the regulation of allergic reactions, although the underlying mechanism remains unclear. Here we show that Sirt1 negatively regulates FcεRI-stimulated mast cell activation and anaphylaxis through two mutually regulated pathways involving AMP-activated protein kinase (AMPK) and protein tyrosine phosphatase 1B (PTP1B). Mast cell-specific knockout of Sirt1 dampened AMPK-dependent suppression of FcεRI signaling, thereby augmenting mast cell activation both in vitro and in vivo. Sirt1 inhibition of FcεRI signaling also involved an alternative component, PTP1B, which attenuated the inhibitory AMPK pathway and conversely enhanced the stimulatory Syk pathway, uncovering a novel role of this phosphatase. Moreover, a Sirt1 activator resveratrol stimulated the inhibitory AMPK axis, with reciprocal suppression of the stimulatory PTP1B/Syk axis, thus potently inhibiting anaphylaxis. Overall, our results provide a molecular explanation for the beneficial role of Sirt1 in allergy and underscore a potential application of Sirt1 activators as a new class of anti-allergic agents.

The orphan nuclear receptor NR4A1 promotes FcεRI‐stimulated mast cell activation and anaphylaxis by counteracting the inhibitory LKB1/AMPK axis

“…A previous study reported that NR4A1 suppresses AMPK phosphorylation at Thr172 by inhibiting LKB1 binding to AMPK in human hepatocytes . Since the LKB1/AMPK axis negatively regulates mast cell activation, we examined the impact of NR4A1 knockdown (Figure A), knockout (Figure B), and overexpression (Figure C) on LKB1/AMPK signaling in BMMCs. As reported previously, LKB1 and AMPK were constitutively active in mast cells, and IgE/Ag stimulation reduced their phosphorylation, resulting in efficient activation of FcεRI signaling components including PLCγ1, ERK, JNK, and IKK, but not Akt, p38 MAPK, or Syk, a primary FcεRI‐proximal tyrosine kinase.…”

“…Since the LKB1/AMPK axis negatively regulates mast cell activation, we examined the impact of NR4A1 knockdown (Figure A), knockout (Figure B), and overexpression (Figure C) on LKB1/AMPK signaling in BMMCs. As reported previously, LKB1 and AMPK were constitutively active in mast cells, and IgE/Ag stimulation reduced their phosphorylation, resulting in efficient activation of FcεRI signaling components including PLCγ1, ERK, JNK, and IKK, but not Akt, p38 MAPK, or Syk, a primary FcεRI‐proximal tyrosine kinase. Notably, phosphorylation of LKB1/AMPK and its downstream mediator acetyl‐CoA carboxylase (ACC) was significantly increased by siRNA silencing (Figure A) and genetic knockout (Figure B) of NR4A1, whereas it was conversely decreased by adenoviral overexpression of NR4A1 (Figure C), suggesting that NR4A1 attenuates LKB1/AMPK signaling in BMMCs.…”

“…These signaling events toward mast cell activation are counter‐regulated by negative signaling pathways involving tyrosine phosphatases, inhibitory kinases, and ubiquitin ligases . In addition, our recent studies revealed that adenosine monophosphate (AMP)‐activated protein kinase (AMPK) and its upstream kinase, liver kinase B1 (LKB1), are involved in the negative regulation of FcεRI‐induced mast cell activation, and their activities are regulated by sirtuin 1 (SIRT1) and extracellular‐regulated kinase (ERK) in positive and negative manners, respectively . Since the incidence of allergic diseases such as atopic dermatitis and asthma is increasing in developed countries, uncovering novel molecular mechanisms that manipulate mast cell activation could provide crucial insights into the pathophysiology of allergic diseases.…”

“…As such, disruption of the NR4A1‐LKB1 interaction by ethyl 2‐[2,3,4‐trimethoxy‐6‐(1‐octanoyl)phenyl]acetate (TMPA), an NR4A1 antagonist that binds to the ligand‐binding domain of NR4A1, induces LKB1 nuclear export and AMPK activation, thereby lowering blood glucose levels in diabetic mice . Considering that LKB1/AMPK has a negative regulatory role in FcεRI‐driven mast cell activation, we hypothesized that NR4A1 could regulate mast cell activation by modulating the LKB1/AMPK pathway. In this study, we provide unequivocal evidence, using pharmacological and genetic approaches, that NR4A1 acts as a positive regulator of IgE/Ag‐stimulated mast cell activation and anaphylaxis by counteracting the inhibitory LKB1/AMPK axis.…”

Angiogenic Host Defense Peptide AG-30/5C and Bradykinin B2 Receptor Antagonist Icatibant Are G Protein Biased Agonists for MRGPRX2 in Mast Cells

“…These findings raise the interesting possibility that if AG-30/5C activates human MC via MRGPRX2, it may act either as a balanced or biased agonist for the receptor. The stilbenoid resveratrol activates sirtuin 1 (sirt1) to inhibit IgEmediated MC degranulation (33). A recent screen of the National Institutes of Health (NIH) Clinical Collection library led to the identification of resveratrol as an inhibitor of MRGPRX2-mediated Tango (34).…”