Structural analysis of TrkA mutations in patients with congenital insensitivity to pain reveals PLCγ as an analgesic drug target

Abstract

Chronic pain is a major health issue, and the search for new analgesics has become increasingly important because of the addictive properties and unwanted side effects of opioids. To explore potentially new drug targets, we investigated mutations in the NTRK1 gene found in individuals with congenital insensitivity to pain with anhidrosis (CIPA). NTRK1 encodes tropomyosin receptor kinase A (TrkA), the receptor for nerve growth factor (NGF) and that contributes to nociception. Molecular modeling and biochemical analysis identified mutations that decreased the interaction between TrkA and one of its substrates and signaling effectors, phospholipase Cγ (PLCγ). We developed a cell-permeable phosphopeptide derived from TrkA (TAT-pQYP) that bound the Src homology domain 2 (SH2) of PLCγ. In HEK-293T cells, TAT-pQYP inhibited the binding of heterologously expressed TrkA to PLCγ and decreased NGF-induced, TrkA-mediated PLCγ activation and signaling. In mice, intraplantar administration of TAT-pQYP decreased mechanical sensitivity in an inflammatory pain model, suggesting that targeting this interaction may be analgesic. The findings demonstrate a strategy to identify new targets for pain relief by analyzing the signaling pathways that are perturbed in CIPA.

Abstract

A peptide designed from insight into a pain insensitivity disorder is analgesic in mice.

Trk’ing mutations for pain relief

The nerve growth factor receptor TrkA is an attractive target for alleviating pain. However, TrkA mediates other signaling pathways that are critical to neuronal function and survival. To find targets specifically within its pain-mediating pathways, Moraes et al. examined the structural consequences of TrkA mutations that cause a pain insensitivity disorder called CIPA. They found mutations that disrupted the interaction of TrkA with one of its downstream effectors, PLCγ, and designed a peptide to similarly disrupt the interaction in cultured cells. Treating mice with the peptide reduced sensitivity to painful inflammation, suggesting that further analysis of other CIPA-associated mutations may reveal additional targets to explore for alleviating pain.