| Summary: | Sphingolipid activator proteins (saposins A, B, C, and D) are derived from a common precursor protein (prosaposin) and specifically activate in vivo degradation of glycolipids with short carbohydrate chains. A mouse model of prosaposin deficiency (prosaposin−/−) closely mimics the human disease with an elevation of multiple glycolipids. The recently developed saposin A−/− mice showed a chronic form of globoid cell leukodystrophy, establishing the essential in vivo role of saposin A as an activator for galactosylceramidase to degrade galactosylceramide. Seminolipid, the principal glycolipid in spermatozoa, and its precursor/degradative product, galactosylalkylacylglycerol (GalEAG), were analyzed in the testis of the two mouse mutants by electrospray ionization mass spectrometry.Saposin A−/− mice showed the normal seminolipid level, while that of prosaposin−/− mice was ∼150% of the normal level at the terminal stage. In contrast, GalEAG increased up to 10 times in saposin A−/− mice, whereas it decreased with age in the wild-type as well as in prosaposin−/− mice. These analytical findings on the two saposin mutants may shed some light on the physiological function of seminolipid and GalEAG.
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