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Mentions: Hematoxylin and eosin (H&E) stained sections of 15-month-old B−/− mice showed inclusions in a few neurons of spinal cord, brain stem (Fig. 5) and white matter of cerebellum (data not shown). Acoustic ganglion cells in the inner ear also had storage inclusions (Fig. 5). Neuronal cells in dorsal root ganglion contained foamy inclusion material (Fig. 5). To assess the activation of macrophage/microglial cells, anti-CD68 antibody was used to stain the sections. CD68 is an intracellular membrane glycoprotein expressed in quiescent and activated tissue macrophages (35). Positive CD68 staining cells were observed in spinal cord, sciatic nerve, kidney and various regions of brain including thalamus, cortex, cerebellum and brain stem (Fig. 6). Liver, spleen and lung in B−/− mice had background levels of CD68 signal comparable to WT mice. GFAP is an astrocyte marker and enhanced GFAP signal indicates astrogliosis or activated astrocytes. Using anti-GFAP antibody, strong signals were present in the brain stem, corpus callosum, thalamus (Fig. 6), spinal cord and cerebellum (data not shown) of B−/− mice relative to age-matched WT sections. Activation of microglial cells and astrocytes demonstrates proinflammatory responses in the CNS of B−/− mice.
Neurological deficits and glycosphingolipid accumulation in saposin B deficient mice
Bottom Line: Alcian blue positive (sulfatide) storage cells were found in the brain, spinal cord and kidney.These findings delineate the roles of saposin B for the in vivo degradation of several GSLs and its primary function in maintenance of CNS function.B-/- provide a useful model for understanding the contributions of this saposin to GSL metabolism and homeostasis.
Affiliation: Division of Human Genetics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229-3039, USA.
Saposin B derives from the multi-functional precursor, prosaposin, and functions as an activity enhancer for several glycosphingolipid (GSL) hydrolases. Mutations in saposin B present in humans with phenotypes resembling metachromatic leukodystrophy. To gain insight into saposin B's physiological functions, a specific deficiency was created in mice by a knock-in mutation of an essential cysteine in exon 7 of the prosaposin locus. No saposin B protein was detected in the homozygotes (B-/-) mice, whereas prosaposin, and saposins A, C and D were at normal levels. B-/- mice exhibited slowly progressive neuromotor deterioration and minor head tremor by 15 months. Excess hydroxy and non-hydroxy fatty acid sulfatide levels were present in brain and kidney. Alcian blue positive (sulfatide) storage cells were found in the brain, spinal cord and kidney. Ultrastructural analyses showed lamellar inclusion material in the kidney, sciatic nerve, brain and spinal cord tissues. Lactosylceramide (LacCer) and globotriaosylceramide (TriCer) were increased in various tissues of B-/- mice supporting the in vivo role of saposin B in the degradation of these lipids. CD68 positive microglial cells and activated GFAP positive astrocytes showed a proinflammatory response in the brains of B-/- mice. These findings delineate the roles of saposin B for the in vivo degradation of several GSLs and its primary function in maintenance of CNS function. B-/- provide a useful model for understanding the contributions of this saposin to GSL metabolism and homeostasis.
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