Quantifying 1-deoxydihydroceramides and 1-deoxyceramides in mouse nervous system tissue

Accumulation of deoxysphingolipids (deoxySLs) has been implicated in many neural diseases, although mechanisms remain unclear. A major obstacle limiting understanding of deoxySLs has been the lack of a method easily defining measurement of deoxydihydroceramide (deoxydhCer) and deoxyceramide (deoxyCer) in neural tissues. Furthermore, it is poorly understood if deoxySLs accumulate in the nervous system with aging. To facilitate investigation of deoxydhCer and deoxyCer in nervous system tissue, we developed a method to evaluate levels of these lipids in mouse brain, spinal cord, and sciatic nerve. Many deoxydhCers and brain C24-deoxyCer were present at 1, 3, and 6 months of age. Furthermore, while ceramide levels decreased with age, deoxydhCers increased in sciatic nerve and spinal cord, suggesting they may accumulate in peripheral nerves. C22-deoxydhCer was the highest deoxydhCer species in all tissues, suggesting it may be important physiologically. The development of this method will facilitate straightforward profiling of deoxydhCers and deoxyCers and the study of their metabolism and function. These results also reveal that deoxydhCers accumulate in peripheral nerves with normal aging.

Deoxysphingolipid precursors indicate abnormal sphingolipid metabolism in individuals with primary and secondary disturbances of serine availability

Patients with primary serine biosynthetic defects manifest with intellectual disability, microcephaly, ichthyosis, seizures and peripheral neuropathy. The underlying pathogenesis of peripheral neuropathy in these patients has not been elucidated, but could be related to a decrease in the availability of certain classical sphingolipids, or to an increase in atypical sphingolipids. Here, we show that patients with primary serine deficiency have a statistically significant elevation in specific atypical sphingolipids, namely deoxydihydroceramides of 18-22 carbons in acyl length. We also show that patients with aberrant plasma serine and alanine levels secondary to mitochondrial disorders also display peripheral neuropathy along with similar elevations of atypical sphingolipids. We hypothesize that the etiology of peripheral neuropathy in patients with primary mitochondrial disorders is related to this elevation of deoxysphingolipids, in turn caused by increased availability of alanine and decreased availability of serine. These findings could have important therapeutic implications for the management of these patients.