Targeting ASK1 signaling in neurodegeneration: molecular insights and therapeutic promise

Apoptosis signal-regulating kinase 1 (ASK1), a redox-sensitive member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, is a master regulator of neuronal apoptosis as well as neuroinflammation in neurodegenerative disorders (NDs). Under oxidative and endoplasmic reticulum stress conditions, ASK1 sets off a series of pathways, ultimately leading to impairment of cellular functions and the cell's demise. The comprehensive review focuses on the diverse contributions of ASK1 to neurodegeneration driven by Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Human and animal evidence links dysregulated ASK1 signaling is related to amyloid deposition, tau hyperphosphorylation, neuroinflammation, abnormal protein folding, and subsequent neurodegeneration. ASK1 plays a role in tau hyperphosphorylation and amyloid-beta-induced neurotoxicity in AD. ASK1-mediated apoptosis of dopaminergic neurons caused by oxidative stress and aggregation of α-synuclein contributes to PD. Furthermore, ASK1 activation is associated with motor neuron degeneration in ALS related to endoplasmic reticulum stress caused by mutant SOD1. Moreover, the pathogenesis of HD involves the activation of ASK1 by the cellular stress caused by mutant huntingtin protein. ASK1 signaling potentiates inflammatory signals in MS because it is involved in demyelination and neuronal injury. Nonetheless, obstacles persist such as developing brain-targeted therapies, reducing adverse systemic effects, and defining disease-stage-specific functions of ASK1. This review aims to comprehensively examine the role of ASK1 signaling in major NDs, discuss its upstream and downstream regulatory mechanisms, and evaluate the current and emerging therapeutic strategies targeting ASK1.