The Intricate Relationship of Trk Receptors in Brain Diseases and Disorders

The tropomyosin-related tyrosine kinases or neurotrophic tyrosine kinase receptors are a group of tyrosine kinases that play a crucial role in regulating neuronal growth and development. Neurotrophins are a class of protein-secreting cells that serve as the primary ligand for the Trk receptors. The four primary neurotrophins are nerve growth factor (NGF), brain-derived nerve factor (BDNF), neurotrophin-3, and neurotrophin-4/5. Mounting evidence suggests that Trk receptors can be categorized into three types: TrkA, TrkB, and TrkC. These receptors play a crucial role in facilitating neuronal growth and development. Trk receptors influence the survival and differentiation of neurons via many signalling cascades. Neurotrophin interaction with Trk receptors triggers a signalling cascade involving PLC, PI3K/Akt, and Ras/MAPK signalling pathways. Emerging evidence suggests that diminished neurotrophic support, changes in Trk receptor expression, or disruptions in signalling cascades play a crucial role in the development of various neurological disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), autism spectrum disorder (ASD), and many more. This review specifically explores therapeutic approaches targeting Trk receptors, their ligands, and Trk signaling in the context of various brain disorders. We focus on the potential for modulating or inhibiting Trk receptors as a treatment strategy for brain diseases.