Kuan Chien-Tsun, Chang Jinli, Mansson Jan-Eric, Li Jianjun, Pegram Charles, Fredman Pam, McLendon Roger E, Bigner Darell D
Department of Pathology, Duke University Medical Center, Durham, NC 27710, USA.
BMC Dev Biol. 2010 Nov 18;10:114. doi: 10.1186/1471-213X-10-114.
Ganglioside biosynthesis occurs through a multi-enzymatic pathway which at the lactosylceramide step is branched into several biosynthetic series. Lc3 synthase utilizes a variety of galactose-terminated glycolipids as acceptors by establishing a glycosidic bond in the beta-1,3-linkage to GlcNaAc to extend the lacto- and neolacto-series gangliosides. In order to examine the lacto-series ganglioside functions in mice, we used gene knockout technology to generate Lc3 synthase gene B3gnt5-deficient mice by two different strategies and compared the phenotypes of the two null mouse groups with each other and with their wild-type counterparts.
B3gnt5 gene knockout mutant mice appeared normal in the embryonic stage and, if they survived delivery, remained normal during early life. However, about 9% developed early-stage growth retardation, 11% died postnatally in less than 2 months, and adults tended to die in 5-15 months, demonstrating splenomegaly and notably enlarged lymph nodes. Without lacto-neolacto series gangliosides, both homozygous and heterozygous mice gradually displayed fur loss or obesity, and breeding mice demonstrated reproductive defects. Furthermore, B3gnt5 gene knockout disrupted the functional integrity of B cells, as manifested by a decrease in B-cell numbers in the spleen, germinal center disappearance, and less efficiency to proliferate in hybridoma fusion.
These novel results demonstrate unequivocally that lacto-neolacto series gangliosides are essential to multiple physiological functions, especially the control of reproductive output, and spleen B-cell abnormality. We also report the generation of anti-IgG response against the lacto-series gangliosides 3'-isoLM1 and 3',6'-isoLD1.
神经节苷脂的生物合成通过多酶途径进行，在乳糖基神经酰胺步骤分支为几个生物合成系列。Lc3合酶通过在β-1,3-连接中与GlcNAc建立糖苷键，利用多种以半乳糖为末端的糖脂作为受体，以延长乳糖系列和新乳糖系列神经节苷脂。为了研究小鼠中乳糖系列神经节苷脂的功能，我们使用基因敲除技术通过两种不同策略生成Lc3合酶基因B3gnt5缺陷型小鼠，并将两个基因敲除小鼠组的表型相互比较以及与它们的野生型对照进行比较。
B3gnt5基因敲除突变小鼠在胚胎期看起来正常，并且如果它们在分娩后存活下来，在生命早期也保持正常。然而，约9%出现早期生长迟缓，11%在出生后不到2个月死亡，成年小鼠倾向于在5至15个月死亡，表现为脾肿大和明显肿大的淋巴结。没有乳糖-新乳糖系列神经节苷脂，纯合子和杂合子小鼠都逐渐出现掉毛或肥胖，繁殖小鼠表现出生殖缺陷。此外，B3gnt5基因敲除破坏了B细胞的功能完整性，表现为脾脏中B细胞数量减少、生发中心消失以及在杂交瘤融合中增殖效率降低。
这些新结果明确表明，乳糖-新乳糖系列神经节苷脂对多种生理功能至关重要，尤其是对生殖输出的控制和脾脏B细胞异常。我们还报告了针对乳糖系列神经节苷脂3'-isoLM1和3',6'-isoLD1产生的抗IgG反应。
