Buccinnà Barbara, Piccinini Marco, Prinetti Alessandro, Scandroglio Federica, Prioni Simona, Valsecchi Manuela, Votta Barbara, Grifoni Silvia, Lupino Elisa, Ramondetti Cristina, Schuchman Edward H, Giordana Maria Teresa, Sonnino Sandro, Rinaudo Maria Teresa
Departments of Medicine and Experimental Oncology, Section of Biochemistry, University of Turin, Turin, Italy.
J Neurochem. 2009 Apr;109(1):105-15. doi: 10.1111/j.1471-4159.2009.05947.x. Epub 2009 Feb 2.
Niemann-Pick disease (NPD) type A is a neurodegenerative disorder caused by sphingomyelin (SM) accumulation in lysosomes relying on reduced or absent acid sphingomyelinase (ASM) activity. NPD-A patients develop progressive neurodegeneration including cerebral and cerebellar atrophy, relevant Purkinje cell and myelin deficiency with death within 3 years. ASM'knock-out' (ASMKO) mice, an animal model of NPD-A, develop a phenotype largely mimicking that of NPD-A. The mechanisms underlying myelin formation are poorly documented in ASMKO mice. In this study we determined the content of four myelin-specific proteins, myelin basic protein (MBP), 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), myelin associated glycoprotein (MAG) and proteolipid protein (PLP), and that of myelin-enriched sphingolipids in the brains of ASMKO and wild-type mice in early stages of post-natal (pn) life. Protein and mRNA analysis revealed that in ASMKO mice beginning from 4 post-natal weeks (wk-pn), the expression levels of MAG, CNP, and MBP were below those observed in wild-type mice and the same applied to PLP at 10 wk-pn. Moreover, at 4 wk-pn the expression of SOX10, one of the transcription factors involved in oligodendrocyte development and maintenance was lower in ASMKO mice. Lipid analysis showed that SM and the gangliosides GM3 and GM2 accumulated in the brains of ASMKO mice, as opposed to galactocerebroside and galactosulfocerebroside that, in parallel with the mRNAs of UDP-galactose ceramide galactosyltransferase and galactose-3-O-sulfotransferase 1, the two transferases involved in their synthesis, decreased. Myelin lipid analysis showed a progressive sphingomyelin accumulation in ASMKO mice; noteworthy, of the two sphingomyelin species known to be resolved by TLC, only that with the lower Rf accumulated. The immunohistochemical analysis showed that the reduced expression of myelin specific proteins in ASMKO mice at 10 wk-pn was not restricted to the Purkinje layer of the cerebellar cortex but involved the cerebral cortex as well. In conclusion, reduced oligodendrocyte metabolic activity is likely to be the chief cause of myelin deficiency in ASMKO mice, thus shedding light on the molecular dysfunctions underlying neurodegeneration in NPD-A.
A型尼曼-匹克病（NPD）是一种神经退行性疾病，由溶酶体中鞘磷脂（SM）积累所致，这依赖于酸性鞘磷脂酶（ASM）活性降低或缺乏。NPD-A患者会出现进行性神经退行性变，包括大脑和小脑萎缩、相关的浦肯野细胞和髓鞘缺乏，3年内死亡。ASM“敲除”（ASMKO）小鼠是NPD-A的动物模型，其表现型在很大程度上模仿NPD-A。ASMKO小鼠中髓鞘形成的潜在机制记录较少。在本研究中，我们测定了出生后（pn）早期ASMKO小鼠和野生型小鼠大脑中四种髓鞘特异性蛋白，即髓鞘碱性蛋白（MBP）、2',3'-环核苷酸3'-磷酸二酯酶（CNP）、髓鞘相关糖蛋白（MAG）和蛋白脂蛋白（PLP）的含量，以及富含髓鞘的鞘脂的含量。蛋白质和mRNA分析显示，从出生后4周（wk-pn）开始，ASMKO小鼠中MAG、CNP和MBP的表达水平低于野生型小鼠，10 wk-pn时PLP的情况也相同。此外，在4 wk-pn时，参与少突胶质细胞发育和维持的转录因子之一SOX10在ASMKO小鼠中的表达较低。脂质分析表明，ASMKO小鼠大脑中SM以及神经节苷脂GM3和GM2积累，相反，半乳糖脑苷脂和半乳糖硫酸脑苷脂以及参与其合成的两种转移酶，即UDP-半乳糖神经酰胺半乳糖基转移酶和半乳糖-3-O-磺基转移酶1的mRNA则减少。髓鞘脂质分析显示ASMKO小鼠中鞘磷脂逐渐积累；值得注意的是，已知通过薄层层析可分离的两种鞘磷脂中，只有Rf较低的那种积累。免疫组织化学分析表明，10 wk-pn时ASMKO小鼠中髓鞘特异性蛋白表达降低不仅限于小脑皮质的浦肯野层，还涉及大脑皮质。总之，少突胶质细胞代谢活性降低可能是ASMKO小鼠髓鞘缺乏的主要原因，从而揭示了NPD-A神经退行性变潜在的分子功能障碍。
