TDP-43 as a therapeutic target in neurodegenerative diseases: Focusing on motor neuron disease and frontotemporal dementia

A common feature of adult-onset neurodegenerative diseases is the presence of characteristic pathological accumulations of specific proteins. These pathological protein depositions can vary in their protein composition, cell-type distribution, and intracellular (or extracellular) location. For example, abnormal cytoplasmic protein deposits which consist of the TDP-43 protein are found within motor neurons in patients with amyotrophic lateral sclerosis (ALS, a common form of motor neuron disease) and frontotemporal dementia (FTD). The presence of these insoluble intracellular TDP-43 inclusions suggests that restoring TDP-43 homeostasis represents a potential therapeutical strategy, which has been demonstrated in alleviating neurodegenerative symptoms in cell and animal models of ALS/FTD. We have reviewed the mechanisms that lead to disrupted TDP-43 homeostasis and discussed how small molecule-based therapies could be applied in modulating these mechanisms. This review covers recent advancements and challenges in small molecule-based therapies that could be used to clear pathological forms of TDP-43 through various protein homeostasis mechanisms and advance the way towards finding effective therapeutical drug discoveries for neurodegenerative diseases characterized by TDP-43 proteinopathies, especially ALS and FTD. We also consider the wider insight of these therapeutic strategies for other neurodegenerative diseases.