Saturated fats accelerate neurodegeneration in multiple sclerosis

Researchers identify enzymes ceramide synthase 5 and 6 as key players in how saturated fats worsen multiple sclerosis symptoms.

In a recent study published in Glia, researchers examined how the synthesis of the sphingolipid ceramide C16 from palmitic acid impacted the severity of neurodegenerative diseases such as multiple sclerosis.

The study used murine models of neurodegenerative diseases to examine whether inhibiting specific enzymes involved in ceramide C16 production reduced disease severity.

Background

Sphingolipids are important components of the cell membrane, especially in the brain and the myelin sheath on neurons, and play crucial roles in cell signaling. However, high levels of specific sphingolipids such as ceramides have been observed in various neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, and multiple sclerosis.

Recent studies have found elevated levels of ceramide C16 associated with increased cognitive decline and worse disease outcomes in individuals with multiple sclerosis and Alzheimer’s disease, especially among people with high body mass index or those who consume diets rich in saturated fats.

Ceramide C16 is produced either de novo using substrates such as palmitic acid (abundant in palm oil) or through the breakdown of other sphingolipids. The synthesis of ceramide C16 from saturated fats relies on specific enzymes. It is influenced by diets containing processed foods rich in fatty acids, which increase ceramide levels and worsen neurodegenerative conditions.

About the study

In the present study, the researchers used murine models that were neuronal knockouts for the genes encoding the enzymes ceramide synthases (CerS). The genes encoding the enzymes CerS5 and CerS6, which synthesize the ceramides C14 and C16, were knocked out using mice with ‘floxed’ alleles, which are genes that have been modified to allow selective deletion.

The mice were then induced with experimental autoimmune encephalomyelitis to create a murine model of multiple sclerosis, for which they were injected with a specific myelin peptide and an adjuvant, and pertussis toxin was administered to increase disease severity.

Additionally, the researchers derived primary neuronal cultures from rat embryo hippocampi and the hippocampal and cortical tissue of mouse embryos. The rat neuronal cells were then exposed to hydrogen peroxide to simulate oxidative stress, while the mouse neuronal cells were exposed to palmitic acid and hydrogen peroxide to simulate metabolic and oxidative stress, respectively.

Quantitative real-time polymerase chain reaction (RT-qPCR) was then conducted to measure the levels of messenger ribonucleic acid (mRNA) in the neuron and spinal cord samples, which allowed the researchers to analyze gene expression. The mRNA was converted to complementary deoxyribonucleic acid (cDNA) through reverse transcription, after which the cDNA was amplified and quantified to assess gene expression levels.

The study also included in situ hybridization experiments, where the mouse brains were sectioned and processed to detect specific gene transcripts of CerS5 and CerS6 genes. The BaseScope assay, using labeled probes that bind specifically to target mRNA, was performed to detect the ceramide synthase gene transcripts.

The brain tissue sections were also stained with antibodies specific for oligodendrocytes, neurons, and astrocytes to identify the cell types. The labeled sections were then visualized using confocal microscopy, which allowed the researchers to observe the mRNA expression in different cell types.

Results

The results reported that lowering the production of ceramide C16 in the neurons offered neuroprotection in the murine multiple sclerosis model with experimental autoimmune encephalomyelitis.

Specifically, deleting the CerS6 enzyme, which produces ceramide C16, in the excitatory neurons resulted in reduced disease severity and delayed onset of the disease, but only when the mouse was fed regular chow. When the mice were fed a high-fat diet, the neuroprotective effect of CerS6 deletion was lost, which the researchers proposed was due to the increased activity of the CerS5 enzyme, which can also produce ceramide C16.

Furthermore, when both CerS5 and CerS6 were deleted, the disease severity was lower even when the mice were fed the high-fat diet enriched with palmitic acid. This supported the finding that inhibiting the synthesis of ceramide C16 could reduce the severity of experimental autoimmune encephalomyelitis and multiple sclerosis.

The study also found that ceramide C16 accumulation in the neurons affected mitochondrial function. When the neurons lacking the enzymes that produce ceramide C16 were exposed to palmitic acid, their mitochondria were more resilient, indicating that ceremide C16 accumulation compromised mitochondrial integrity in multiple sclerosis patients.

Conclusions

To summarize, the study found that limiting the synthesis of ceramide C16 in the neurons by targeting the enzymes CerS5 and CerS6 could be a potential therapeutic strategy to reduce disease severity and offer neuroprotective effects in multiple sclerosis patients. Dietary modifications consisting of lower fatty acid consumption, especially of palmitic acid sources such as palm oil, could also help in mitigating disease severity in demyelinating disorders.