Organelle Dysfunction in Neurodegenerative Disease: From Lysosomal Failure to Therapeutic Opportunity

Why Organelle Dysfunction Drives Neurodegeneration

Neurodegenerative diseases — including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS) — collectively affect over 50 million people worldwide and represent one of the largest unmet needs in modern medicine. Despite decades of investment, disease-modifying treatments remain limited. A growing body of evidence points to a convergent, subcellular explanation: dysfunction of intracellular organelles^7,10.

Neurons are uniquely vulnerable cells. Unlike most tissues, they cannot upregulate glycolysis to compensate for energy deficits, making them critically dependent on mitochondrial oxidative phosphorylation. They are also long-lived, non-dividing cells that accumulate damaged proteins over decades — rendering the efficiency of lysosomal protein degradation and autophagy essential for long-term survival. When these organelle systems fail, even subtly, the consequences are progressive and largely irreversible.

The Lysosome, Mitochondria, and ER Network in Neurodegeneration

Intracellular organelles are not isolated compartments — they form a dynamic, physically interconnected network communicating through membrane contact sites (MCSs) that exchange calcium, lipids, and metabolic signals. Three organelles are particularly central to neurodegeneration:

Lysosomes and the autophagy-lysosome pathway

Lysosomes are the primary degradative organelles of the cell, functioning as the endpoint of the autophagy-lysosome pathway (ALP). They maintain an acidic lumen (pH 4.5–5.5) that is essential for the activity of hydrolytic enzymes including glucocerebrosidase (GCase), cathepsins B/D, and over 60 other lysosomal hydrolases. In neurodegenerative diseases, lysosomal acidification failure, impaired enzyme activity, and defective vesicular trafficking converge to prevent the clearance of misfolded proteins — including alpha-synuclein (PD), amyloid-beta and tau (AD), and mutant huntingtin (HD). This proteostatic failure is now recognised as a unifying mechanism across the major neurodegenerative diseases^8,9.

Mitochondrial dysfunction and bioenergetic failure

Mitochondria sustain neuronal survival through oxidative phosphorylation, calcium homeostasis, and regulation of apoptosis. Mitochondrial dysfunction in neurodegeneration manifests with decreased ATP production, elevated reactive oxygen species (ROS), loss of mitochondrial membrane potential, and impaired mitophagy — the selective autophagy of damaged mitochondria. Dysfunctional mitochondria that escape clearance become destructive, activating the intrinsic cell death pathway. Given that neurons cannot compensate through glycolysis, mitochondrial bioenergetic failure represents a direct route to neuronal death.

Endoplasmic reticulum stress

The endoplasmic reticulum (ER) is the entry point of the secretory pathway and a major hub for calcium signalling. In neurodegenerative conditions, accumulation of misfolded proteins in the ER lumen triggers the unfolded protein response (UPR), which, when chronic, drives neuroinflammation and apoptosis. ER–lysosome and ER–mitochondria contact sites are particularly sensitive to disruptions in protein trafficking and calcium homeostasis, meaning ER stress frequently amplifies downstream lysosomal and mitochondrial dysfunction.