Cellular mechanism of U18666A-mediated apoptosis in cultured murine cortical neurons: Bridging Niemann–Pick disease type C and Alzheimer's disease

Neuronal cell death can occur by means of either necrosis or apoptosis. Both necrosis and apoptosis are generally believed to be distinct mechanisms of cell death with different characteristic features distinguished on the basis of their morphological and biochemical properties. The brain is the most cholesterol-rich organ in the body but not much is known about the mechanisms that regulate cholesterol homeostasis in the brain. Recently, several clinical and biochemical studies suggest that cholesterol imbalance in the brain may be a risk factor related to the development of neurological disorders such as Niemann–Pick disease type C (NPC) and Alzheimer's disease (AD). NPC is a fatal juvenile neurodegenerative disorder characterized by premature neuronal death and somatically altered cholesterol metabolism. The main biochemical manifestation in NPC is elevated intracellular accumulation of free cholesterol caused by a genetic deficit in cholesterol trafficking. The pharmacological agent, U18666A (3-β-[2-(diethylamino)ethoxy]androst-5-en-17-one), is a well-known class-2 amphiphile which inhibits cholesterol transport. Cells treated with this agent accumulate intracellular cholesterol to massive levels, similar to that observed in cells from NPC patients. NPC and AD have some pathological similarities which may share a common underlying cause. AD is one of the most common types of dementia affecting the elderly. However, the molecular mechanisms of neurodegeneration in NPC and AD are largely unknown. This review provides a consolidation of work done using U18666A in the past half century and focuses on the implications of our research findings on the mechanism of U18666A-mediated neuronal apoptosis in primary cortical neurons, which may provide an insight to elucidate the mechanisms of neurodegenerative diseases, particularly NPC and AD, where apoptosis might occur through a similar mechanism.