Targeted Protein Degradation for Neurodegenerative Disorders

Abstract

Targeted protein degradation (TPD) is an innovative therapeutic strategy that leverages the cell’s natural proteolytic machinery to selectively remove pathologic proteins implicated in neurodegenerative disorders. As these conditions are characterized by aberrant protein accumulation, TPD technologies such as proteolysis-targeting chimeras (PROTACs) and molecular glues offer a promising avenue to address the underlying molecular pathology. This review synthesizes current evidence, elucidates mechanisms, and highlights clinical and translational advances in TPD for neurodegenerative diseases, providing a comprehensive resource for clinicians and medical researchers.

Introduction

Neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS), present formidable challenges due to progressive neuronal loss and accumulation of misfolded proteins. Traditional therapies provide symptomatic relief but often fail to modify disease progression. Recent advances in targeted protein degradation have opened new therapeutic frontiers by enabling the selective elimination of disease-driving proteins. This article explores the scientific rationale, clinical relevance, and emerging therapeutic opportunities of TPD in neurodegenerative care, emphasizing mechanisms, evidence, and practical implications for healthcare professionals.

Epidemiology / Disease Burden

Neurodegenerative disorders collectively account for a significant proportion of global morbidity and mortality. Alzheimer’s disease affects over 55 million people worldwide, with projections indicating a doubling of cases by 2050. Parkinson’s disease is the second most prevalent, affecting more than 10 million individuals, while ALS and HD, though less common, contribute substantially to disability and healthcare costs. The socioeconomic impact is profound, with costs exceeding hundreds of billions of dollars annually, underscoring the urgent need for disease-modifying interventions.

Pathophysiology

The pathogenesis of neurodegenerative diseases is intricately linked to the misfolding, aggregation, and impaired clearance of specific proteins. In AD, the accumulation of β-amyloid plaques and tau neurofibrillary tangles disrupts synaptic function and triggers neuroinflammation. PD is characterized by α-synuclein aggregation into Lewy bodies, while HD involves expanded huntingtin protein with pathogenic polyglutamine tracts. ALS features cytoplasmic inclusions of TDP-43 and other proteins. Cellular proteostasis mechanisms, including the ubiquitin-proteasome system (UPS) and autophagy-lysosome pathway, become overwhelmed or dysfunctional, facilitating toxic protein buildup and neuronal death. TPD strategies aim to hijack or augment these endogenous systems to restore proteostasis and halt neurodegeneration.

Risk Factors

Genetic predisposition, advancing age, environmental exposures, and lifestyle factors converge to modulate risk for neurodegenerative disorders. Mutations in genes such as APP, PSEN1/2 (AD), SNCA, LRRK2 (PD), HTT (HD), and C9orf72 (ALS) directly influence protein aggregation propensities. Non-genetic risks include cardiovascular disease, diabetes, traumatic brain injury, and chronic inflammation, which exacerbate cellular stress and proteostatic dysregulation. Understanding these factors is crucial for risk stratification and precision medicine approaches in TPD-based interventions.

Clinical Features

Clinical manifestations of neurodegenerative diseases are diverse but share common themes of cognitive decline (AD), motor dysfunction (PD, HD, ALS), and behavioral alterations. Early symptoms are often subtle and insidious, progressing to severe impairment and loss of independence. Notably, the clinical phenotype reflects the anatomic distribution and burden of pathogenic protein aggregates, making early identification and intervention critical.

Diagnosis

Diagnosis relies on a combination of clinical assessment, neuroimaging, and biomarker evaluation. MRI and PET imaging can reveal atrophy patterns and protein deposition. Cerebrospinal fluid (CSF) analysis quantifies levels of β-amyloid, tau, α-synuclein, and neurofilament light chain. Emerging blood-based biomarkers and genetic testing are enhancing diagnostic accuracy and enabling earlier detection an essential prerequisite for effective TPD therapy deployment.

Treatment & Management

Current management is centered on symptomatic relief via cholinesterase inhibitors (AD), dopaminergic agents (PD), and riluzole or edaravone (ALS). However, these approaches do not arrest disease progression. Supportive care, multidisciplinary rehabilitation, and management of comorbidities remain integral. Disease-modifying therapies that can reduce or eliminate pathological proteins represent a paradigm shift in management strategy.

Recent Advances / Emerging Therapies

TPD technologies are at the forefront of therapeutic innovation. PROTACs are bifunctional molecules that link a target protein to an E3 ubiquitin ligase, facilitating ubiquitination and proteasomal degradation. Molecular glues stabilize interactions between proteins and endogenous E3 ligases, enhancing selective degradation. In preclinical models, PROTACs have demonstrated the ability to degrade tau, α-synuclein, and mutant huntingtin, leading to reduced aggregate load and neuroprotection. Early-phase clinical trials are underway, evaluating the safety and efficacy of TPD agents in AD and PD. Advantages include catalytic mechanism, high specificity, and potential to target previously “undruggable” proteins. Challenges remain regarding blood-brain barrier penetration, off-target effects, and long-term safety.

Guideline Recommendations

While no TPD therapy has yet achieved guideline endorsement for neurodegenerative diseases, regulatory agencies and expert panels acknowledge the promise of this approach. Ongoing clinical trials are expected to inform future recommendations. Interim guidance emphasizes enrolling suitable patients in clinical trials, integrating biomarker-driven selection, and multidisciplinary management to optimize outcomes and safety.

Conclusion

Targeted protein degradation holds transformative potential for the treatment of neurodegenerative disorders by directly addressing the root molecular pathology. With continued advances in medicinal chemistry, delivery systems, and biomarker-guided patient selection, TPD therapies may soon redefine the standard of care. Ongoing research, robust clinical trials, and collaborative translational efforts will be pivotal in realizing the promise of TPD for patients confronting these devastating diseases.