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

Exploring protein-protein interactions for the development of new analgesics

The development of new analgesics has been challenging. Candidate drugs often have limited clinical utility due to side effects that arise because many drug targets are involved in signaling pathways other than pain transduction. Here, we explored the potential of targeting protein-protein interactions (PPIs) that mediate pain signaling as an approach to developing drugs to treat chronic pain. We reviewed the approaches used to identify small molecules and peptide modulators of PPIs and their ability to decrease pain-like behaviors in rodent animal models. We analyzed data from rodent and human sensory nerve tissues to build associated signaling networks and assessed both validated and potential interactions and the structures of the interacting domains that could inform the design of synthetic peptides and small molecules. This resource identifies PPIs that could be explored for the development of new analgesics, particularly between scaffolding proteins and receptors for various growth factors and neurotransmitters, as well as ion channels and other enzymes. Targeting the adaptor function of CBL by blocking interactions between its proline-rich carboxyl-terminal domain and its SH3-domain-containing protein partners, such as GRB2, could disrupt endosomal signaling induced by pain-associated growth factors. This approach would leave intact its E3-ligase functions, which are mediated by other domains and are critical for other cellular functions. This potential of PPI modulators to be more selective may mitigate side effects and improve the clinical management of pain.

Regulating Tumorigenicity and Cancer Metastasis through TRKA Signaling

Tropomyosin receptor kinase (TRK) A, TRKA, is a specific binding receptor of nerve growth factor (NGF), which plays an essential role in the occurrence and progression of human cancers. TRKA overexpression has been proven to be a powerful carcinogenic driver and has been verified in many tumors. The TRKA receptor kinase domain is over-activated in an NGF-dependent manner, accompanied by activation of downstream signal pathways, such as RAS-MAPK, PI3K-AKT, JAK2-STAT3 pathway, PLC γ pathway, and Hippo pathway, which participate in tumor cell proliferation, invasion, epithelial-mesenchymal transition (EMT), perineural invasion (PNI), drug resistance, and cancer pain. In addition, chimeric oncogenes produced by the fusion of NTRK1 and other genes are also the direct cause of tumorigenesis and cancer development. The newly developed TRK inhibitors can improve symptoms and tumor regression in cancer patients with overexpression of TRKA or NTRK1 fusion gene. With the emergence of drug resistance, next generation of TRK inhibitors can still maintain strong clinical efficacy in the case of TRK kinase domain mutations, and these inhibitors are in clinical trials. This review summarizes the characteristics and research progress of TRKA, focusing on the regulatory role of the TRKA signal pathway in different tumors. In addition, we have summarized the clinical significance of TRKA and the TRK inhibitors. This review may provide a new reference for the study of the mechanism of TRKA in different tumors, and also provide a new perspective for the in-depth understanding of the role of TRKA as a biomarker and therapeutic target in human cancer.

Understanding the Structural Requirements of Peptide-Protein Interaction and Applications for Peptidomimetic Development

Protein-protein interaction is at the heart of most biological processes, and small peptides that bind to protein binding sites are resourceful tools to explore and understand the structural requirements for these interactions. In that sense, phage display is a well-suited technology to study protein-protein interactions, as it allows for unbiased screening of billions of peptides in search for those that interact with a protein binding domain. Here, we will illustrate how two distinct but complementary approaches, phage display and nuclear magnetic resonance (NMR), can be utilized to unveil structural details of peptide-protein interaction. Finally, knowledge derived from phage mutagenesis and NMR studies can be streamlined for quick peptidomimetic design and synthesis using the retroinversion approach to validate using in vitro and in vivo assays the therapeutic potential of peptides identified by phage display.

Human TrkAR649W mutation impairs nociception, sweating and cognitive abilities: a mouse model of HSAN IV

A functional nerve growth factor NGF-Tropomyosin Receptor kinase A (TrkA) system is an essential requisite for the generation and maintenance of long-lasting thermal and mechanical hyperalgesia in adult mammals. Indeed, mutations in the gene encoding for TrkA are responsible for a rare condition, named Hereditary Sensory and Autonomic Neuropathy type IV (HSAN IV), characterized by the loss of response to noxious stimuli, anhidrosis and cognitive impairment. However, to date, there is no available mouse model to properly understand how the NGF-TrkA system can lead to pathological phenotypes that are distinctive of HSAN IV. Here, we report the generation of a knock-in mouse line carrying the HSAN IV TrkAR649W mutation. First, by in vitro biochemical and biophysical analyses, we show that the pathological R649W mutation leads to kinase-inactive TrkA also affecting its membrane dynamics and trafficking. In agreement with the HSAN IV human phenotype, TrkAR649W/m mice display a lower response to thermal and chemical noxious stimuli, correlating with reduced skin innervation, in addition to decreased sweating in comparison to TrkAh/m controls. Moreover, the R649W mutation decreases anxiety-like behavior and compromises cognitive abilities, by impairing spatial-working and social memory. Our results further uncover unexplored roles of TrkA in thermoregulation and sociability. In addition to accurately recapitulating the clinical manifestations of HSAN IV patients, our findings contribute to clarifying the involvement of the NGF-TrkA system in pain sensation.

Role of ATP in migraine mechanisms: focus on P2X3 receptors

Migraine is a major health burden worldwide with complex pathophysiology and multifarious underlying mechanisms. One poorly understood issue concerns the early steps in the generation of migraine pain. To elucidate the basic process of migraine pain further, it seems useful to consider key molecular players that may operate synergistically to evoke headache. While the neuropeptide CGRP is an important contributor, we propose that extracellular ATP (that generally plays a powerful nociceptive role) is also a major component of migraine headache, acting in concert with CGRP to stimulate trigeminal nociceptive neurons. The aim of the present focused review is to highlight the role of ATP activating its P2X3 membrane receptors selectively expressed by sensory neurons including their nerve fiber terminals in the meninges. Specifically, we present data on the homeostasis of ATP and related purines in the trigeminovascular system and in the CNS; the basic properties of ATP signalling at peripheral and central nerve terminals; the characteristics of P2X3 and related receptors in trigeminal neurons; the critical speed and persistence of P2X3 receptor activity; their cohabitation at the so-called meningeal neuro-immune synapse; the identity of certain endogenous agents cooperating with ATP to induce neuronal sensitization in the trigeminal sensory system; the role of P2X3 receptors in familial type migraine; the current state of P2X3 receptor antagonists and their pharmacological perspectives in migraine. It is proposed that the unique kinetic properties of P2X3 receptors activated by ATP offer an interesting translational value to stimulate future studies for innovative treatments of migraine pain.