Department of Pediatrics, University of Connecticut School of Medicine, Farmington, CT 06030, USA.
Department of Genetics and Genome Sciences, University of Connecticut Health Center, Farmington, CT 06030, USA.
Int J Mol Sci. 2022 Sep 1;23(17):9944. doi: 10.3390/ijms23179944.
Glycogen storage disease type IX (GSD-IX) constitutes nearly a quarter of all GSDs. This ketotic form of GSD is caused by mutations in phosphorylase kinase (PhK), which is composed of four subunits (α, β, γ, δ). PhK is required for the activation of the liver isoform of glycogen phosphorylase (PYGL), which generates free glucose-1-phosphate monomers to be used as energy via cleavage of the α -(1,4) glycosidic linkages in glycogen chains. Mutations in any of the PhK subunits can negatively affect the regulatory and catalytic activity of PhK during glycogenolysis. To understand the pathogenesis of GSD-IX-beta, we characterized a newly created PHKB knockout (Phkb−/−) mouse model. In this study, we assessed fasting blood glucose and ketone levels, serum metabolite concentrations, glycogen phosphorylase activity, and gene expression of gluconeogenic genes and fibrotic genes. Phkb−/− mice displayed hepatomegaly with lower fasting blood glucose concentrations. Phkb−/− mice showed partial liver glycogen phosphorylase activity and increased sensitivity to pyruvate, indicative of partial glycogenolytic activity and upregulation of gluconeogenesis. Additionally, gene expression analysis demonstrated increased lipid metabolism in Phkb−/− mice. Gene expression analysis and liver histology in the livers of old Phkb−/− mice (>40 weeks) showed minimal profibrogenic features when analyzed with age-matched wild-type (WT) mice. Collectively, the Phkb−/− mouse recapitulates mild clinical features in patients with GSD-IX-beta. Metabolic and molecular analysis confirmed that Phkb−/− mice were capable of sustaining energy homeostasis during prolonged fasting by using partial glycogenolysis, increased gluconeogenesis, and potentially fatty acid oxidation in the liver.
糖原贮积病 IX 型（GSD-IX）构成了所有 GSD 的近四分之一。这种酮体形式的 GSD 是由磷酸化酶激酶（PhK）突变引起的，PhK 由四个亚基（α、β、γ、δ）组成。PhK 是肝糖原磷酸化酶（PYGL）同工型激活所必需的，它通过切割糖原链中的α-（1,4）糖苷键，生成游离的葡萄糖-1-磷酸单体，作为能量使用。PhK 亚基的任何突变都可能在糖原分解过程中对 PhK 的调节和催化活性产生负面影响。为了了解 GSD-IX-β的发病机制，我们对新创建的 PHKB 敲除（Phkb−/−）小鼠模型进行了表征。在这项研究中，我们评估了禁食血糖和酮体水平、血清代谢物浓度、糖原磷酸化酶活性以及糖异生基因和纤维化基因的表达。Phkb−/− 小鼠表现出肝肿大和较低的空腹血糖浓度。Phkb−/− 小鼠表现出部分肝糖原磷酸化酶活性和对丙酮酸的敏感性增加，表明部分糖原分解活性和糖异生的上调。此外，基因表达分析表明 Phkb−/− 小鼠的脂质代谢增加。对>40 周龄的老年 Phkb−/− 小鼠的肝脏进行基因表达分析和组织学检查，与年龄匹配的野生型（WT）小鼠相比，最小的纤维化特征。总的来说，Phkb−/− 小鼠重现了 GSD-IX-β 患者的轻度临床特征。代谢和分子分析证实，Phkb−/− 小鼠能够通过部分糖原分解、增加糖异生和潜在的脂肪酸氧化在肝脏中维持长时间禁食期间的能量稳态。
