Saturated fatty acid-Coenzyme A supplementation restores neuronal energy levels, synaptic function, and protein homeostasis in hereditary spastic paraplegia

Abstract

Hereditary Spastic Paraplegia (HSP) type 54 is a complex childhood autosomal recessive neurodegenerative disorder characterized by impairments in both neuromuscular and cognitive functions. This condition arises from mutations in the DDHD2 gene, which encodes for the phospholipase A1 enzyme DDHD2. Previous research has indicated that loss of DDHD2 results in lipid droplet accumulation in the brain, progressive apoptosis of motor neurons in the spinal cord, a reduction in cardiolipin content, and an increase in reactive oxygen species. However, the precise underlying mechanisms of HSP54 remains unclear. Our recent study demonstrated a robust increase in saturated free fatty acids (sFFAs), particularly myristic acid, during neuronal stimulation and memory acquisition in vivo in the brains of mice and in vitro in primary neurons. This activity-dependent increase of sFFAs was blocked in DDHD2 knockout mice (DDHD2-/-), suggesting that disturbed production of sFFAs underlies the neuronal pathology of HSP54. Here, using electron microscopy (EM) and live-cell confocal imaging, mass spectrometry and proteomics, electric field stimulation, as well as fluorometric and mitochondrial function assays in cultured primary neurons, we discovered that loss of DDHD2 leads to reduced levels of acetyl-coenzyme A (CoA) and ATP. Additionally, DDHD2 deficiency results in impaired respiratory function, altered mitochondrial morphology and distribution, a significant defect in synaptic vesicle recycling with an accumulation of large bulk endosomes in the presynapses, as well as an imbalance in global protein homeostasis. Our study further reveals that the combined administration of myristic acid and CoA (Myr-CoA) fully rescues mitochondrial function and ATP production within 48 hours. This intervention also leads to a marked restoration of neuronal protein homeostasis, providing the first demonstration of a potential combinatory therapeutic intervention for HSP54. Our findings demonstrate that the sFFAs released by the activity of DDHD2 play a central role in maintaining neuronal energy levels, synaptic function, and protein balance. The requirement for DDHD2 lipase activity in these processes can, therefore, be bypassed by supplementation of a preconjugated Myr-CoA.