Cellular and metabolic effects of renin-angiotensin system blockade on glycogen storage disease type I nephropathy.

Glycogen Storage Disease Type I (GSDI) is an inherited disease caused by glucose-6 phosphatase (G6Pase) deficiency, leading to a loss of endogenous glucose production and severe hypoglycemia. Moreover, most GSDI patients develop a chronic kidney disease (CKD) due to lipid accumulation in the kidney. Similar to diabetic CKD, activation of renin-angiotensin system (RAS) promotes renal fibrosis in GSDI. Here, we investigated the physiological and molecular effects of RAS blockers in GSDI patients and mice. A retrospective analysis of renal function was performed in 21 GSDI patients treated with RAS blockers. Cellular and metabolic impacts of RAS blockade were analyzed in K.G6pc-/- mice characterized by G6pc1 deletion in kidneys. GSDI patients started RAS blocker treatment at a median age of 21 years and long-term treatment reduced the progression of CKD in about 50% of patients. However, CKD progressed to kidney failure in 20% of treated patients, requiring renal transplantation. In K.G6pc-/- mice, CKD was associated with an impairment of autophagy and ER stress. RAS blockade resulted in a rescue of autophagy and decreased ER stress, concomitantly with decreased fibrosis and improved renal function, but without impact on glycogen and lipid contents. In conclusion, these data confirm the partial beneficial effect of RAS blockers in the prevention of CKD in GSDI. Mechanistically, we show that these effects are linked to a reduction of cell stress, without affecting metabolism.

Treatment recommendations for glycogen storage disease type IB- associated neutropenia and neutrophil dysfunction with empagliflozin: Consensus from an international workshop.

Glycogen storage disease type Ib (GSD Ib, biallelic variants in SLC37A4) is a rare disorder of glycogen metabolism complicated by neutropenia/neutrophil dysfunction. Since 2019, the SGLT2-inhibitor empagliflozin has provided a mechanism-based treatment option for the symptoms caused by neutropenia/neutrophil dysfunction (e.g. mucosal lesions, inflammatory bowel disease). Because of the rarity of GSD Ib, the published evidence on safety and efficacy of empagliflozin is still limited and does not allow to develop evidence-based guidelines. Here, an international group of experts provides 14 best practice consensus treatment recommendations based on expert practice and review of the published evidence. We recommend to start empagliflozin in all GSD Ib individuals with clinical or laboratory signs related to neutropenia/neutrophil dysfunction with a dose of 0.3-0.4 mg/kg/d given as a single dose in the morning. Treatment can be started in an outpatient setting. The dose should be adapted to the weight and in case of inadequate clinical treatment response or side effects. We strongly recommend to pause empagliflozin immediately in case of threatening dehydration and before planned longer surgeries. Discontinuation of G-CSF therapy should be attempted in all individuals. If available, 1,5-AG should be monitored. Individuals who have previously not tolerated starches should be encouraged to make a new attempt to introduce starch in their diet after initiation of empagliflozin treatment. We advise to monitor certain safety and efficacy parameters and recommend continuous, alternatively frequent glucose measurements during the introduction of empagliflozin. We provide specific recommendations for special circumstances like pregnancy and liver transplantation.

Empagliflozin for treating neutropenia and neutrophil dysfunction in 21 infants with glycogen storage disease 1b.

Empagliflozin has been successfully repurposed for treating neutropenia and neutrophil dysfunction in patients with glycogen storage disease type 1b (GSD 1b), however, data in infants are missing. We report on efficacy and safety of empagliflozin in infants with GSD 1b. This is an international retrospective case series on 21 GSD 1b infants treated with empagliflozin (total treatment time 20.6 years). Before starting empagliflozin (at a median age of 8.1 months with a median dose of 0.3 mg/kg/day) 12 patients had clinical signs and symptoms of neutrophil dysfunction. Six of these previously symptomatic patients had no further neutropenia/neutrophil dysfunction-associated findings on empagliflozin. Eight patients had no signs and symptoms of neutropenia/neutrophil dysfunction before start and during empagliflozin treatment. One previously asymptomatic individual with a horseshoe kidney developed a central line infection with pyelonephritis and urosepsis during empagliflozin treatment. Of the 10 patients who were treated with G-CSF before starting empagliflozin, this was stopped in four and decreased in another four. Eleven individuals were never treated with G-CSF. While in 17 patients glucose homeostasis remained stable on empagliflozin, four showed glucose homeostasis instability in the introductory phase. In 17 patients, no other side effects were reported, while genital (n = 2) or oral (n = 1) candidiasis and skin infection (n = 1) were reported in the remaining four. Empagliflozin had a good effect on neutropenia/neutrophil dysfunction-related signs and symptoms and a favourable safety profile in infants with GSD 1b and therefore qualifies for further exploration as first line treatment.

Glycogen Storage Disease Type I and Bone: Clinical and Cellular Characterization.

Glycogen storage disease (GSD) is the most prevalent inherited disorder of glycogen metabolism for which no causal treatment is available. In recent years, thanks to the improved clinical management, the life expectancy of these patients extended, disclosing previously unidentified adverse conditions in other organs. In this study, we evaluated the clinical bone complications and the cellular responses in 20 patients (aged 14.1 ± 3.4 years) affected by GSD type I. Fragility fractures were reported in 35% of the patients, which were older than unfractured patients. They involved appendicular skeletal segments, while no vertebral deformity was detected. 60% of the patients had a bone mineral density (BMD) "below the expected range for age", and lumbar spine (LS) BMD Z-scores positively correlated with muscle strength. Circulating mineral and bone markers showed reduction in the older subjects, with no increase in the pubertal age. Significant correlations could not be detected between circulating markers and LS BMD Z-scores, except for sclerostin levels, which also correlated with muscle strength. The osteoclasts differentiated from patients' peripheral blood mononuclear cells did not show cell-autonomous alterations. However, circulating osteoclast precursors from healthy individuals cultured in the presence of patients' sera exhibited increased osteoclastogenesis compared to control sera suggesting that GSD type I serum factors could affect osteoclast function in a non-autonomous manner. In contrast, circulating osteoprogenitors were unremarkable.

Aberrant glucose metabolism underlies impaired macrophage differentiation in glycogen storage disease type Ib.

Glycogen storage disease type Ib (GSD-Ib) is an autosomal recessive disorder caused by a deficiency in the glucose-6-phosphate (G6P) transporter (G6PT) that is responsible for transporting G6P into the endoplasmic reticulum. GSD-Ib is characterized by disturbances in glucose homeostasis, neutropenia, and neutrophil dysfunction. Although some studies have explored neutrophils abnormalities in GSD-Ib, investigations regarding monocytes/macrophages remain limited so far. In this study, we examined the impact of G6PT deficiency on monocyte-to-macrophage differentiation using bone marrow-derived monocytes from G6pt-/- mice as well as G6PT-deficient human THP-1 monocytes. Our findings revealed that G6PT-deficient monocytes exhibited immature differentiation into macrophages. Notably, the impaired differentiation observed in G6PT-deficient monocytes seemed to be associated with abnormal glucose metabolism, characterized by enhanced glucose consumption through glycolysis, even under quiescent conditions with oxidative phosphorylation. Furthermore, we observed a reduced secretion of inflammatory cytokines in G6PT-deficient THP-1 monocytes during the inflammatory response, despite their elevated glucose consumption. In conclusion, this study sheds light on the significance of G6PT in monocyte-to-macrophage differentiation and underscores its importance in maintaining glucose homeostasis and supporting immune response in GSD-Ib. These findings may contribute to a better understanding of the pathogenesis of GSD-Ib and potentially pave the way for the development of targeted therapeutic interventions.

Gene therapy for glycogen storage diseases.

Glycogen storage disorders (GSDs) are inherited disorders of metabolism resulting from the deficiency of individual enzymes involved in the synthesis, transport, and degradation of glycogen. This literature review summarizes the development of gene therapy for the GSDs. The abnormal accumulation of glycogen and deficiency of glucose production in GSDs lead to unique symptoms based upon the enzyme step and tissues involved, such as liver and kidney involvement associated with severe hypoglycemia during fasting and the risk of long-term complications including hepatic adenoma/carcinoma and end stage kidney disease in GSD Ia from glucose-6-phosphatase deficiency, and cardiac/skeletal/smooth muscle involvement associated with myopathy +/- cardiomyopathy and the risk for cardiorespiratory failure in Pompe disease. These symptoms are present to a variable degree in animal models for the GSDs, which have been utilized to evaluate new therapies including gene therapy and genome editing. Gene therapy for Pompe disease and GSD Ia has progressed to Phase I and Phase III clinical trials, respectively, and are evaluating the safety and bioactivity of adeno-associated virus vectors. Clinical research to understand the natural history and progression of the GSDs provides invaluable outcome measures that serve as endpoints to evaluate benefits in clinical trials. While promising, gene therapy and genome editing face challenges with regard to clinical implementation, including immune responses and toxicities that have been revealed during clinical trials of gene therapy that are underway. Gene therapy for the glycogen storage diseases is under development, addressing an unmet need for specific, stable therapy for these conditions.

Outcomes of Pediatric Liver Transplantation in Glycogen Storage Disease Type 1b-A Single-Center Experience.

BACKGROUND: Liver transplantation (LT) normalizes fasting tolerance in glycogen storage disease type (GSD) 1b. However, reported outcomes post-LT with respect to correction of neutropenia, infection risk and growth are varied. Sodium-glucose cotransporter-2 (SGLT2) inhibitors have been recently shown to improve neutropenia in GSD1b patients. METHODS: In this single-center retrospective study, we reviewed all children who underwent LT for GSD1b. Neutropenia, dose of granulocyte colony-stimulating factor (G-CSF), unplanned hospital attendance, anthropometrics, graft rejection, survival, and the effects of dapagliflozin were analyzed. Data from protocol biopsies obtained at 1, 5, and 10 years post-LT and immunosuppression levels were collected. RESULTS: Eight children (6 female), all on G-CSF pre-transplant, underwent cadaveric LT for GSD1b at median age 3.6 years (IQR 3.3-5.1) with mean follow-up time of 10.3 years (95% CI 7.5-13.1). Neutrophil count and G-CSF requirement did not improve post-LT. Although a reduction in unplanned hospital attendance due to infection (0.98 [95% CI 0.76-1.26] vs. 0.49 [95% CI 0.41 to 0.57] per person-year, p < 0.01) was observed, gastrointestinal complaints and graft dysfunction accounted for a similar hospitalization burden pre- versus post-LT. Body mass index (BMI) reduced post-LT (Z-score 1.47 [95%CI 0.39-2.23] vs. 0.56 [95% CI -0.74 to 1.45], p = 0.02), with no significant change in height. Although all children and grafts have survived, 75% of recipients developed rejection, despite adequate immunosuppression levels, with two children having been found to have developed significant fibrosis on their 5-year protocol biopsy. Although dapagliflozin allowed cessation of G-CSF, no improvement in neutrophil count was observed. Despite this, a reduction in gastrointestinal and infection-related morbidity was noted following dapagliflozin. CONCLUSION: Although LT normalizes fasting tolerance in GSD1b and reduces hospital attendance due to infection, morbidity from infection and gastrointestinal manifestations persist. Children in our cohort experienced high rates of rejection necessitating titration of immunosuppression to balance risk of infection against organ rejection. Future studies should investigate whether early introduction of SGLT2 inhibitors post-LT impact morbidity in this group.

DBS are suitable for 1,5-anhydroglucitol monitoring in GSD1b and G6PC3-deficient patients taking SGLT2 inhibitors to treat neutropenia.

Glycogen storage disease type Ib (GSD1b) and G6PC3-deficiency are rare autosomal recessive diseases caused by inactivating mutations in SLC37A4 (coding for G6PT) and G6PC3, respectively. Both diseases are characterized by neutropenia and neutrophil dysfunction due to the intracellular accumulation of 1,5-anhydroglucitol-6-phosphate (1,5-AG6P), a potent inhibitor of hexokinases. We recently showed that the use of SGLT2 inhibitor therapy to reduce tubular reabsorption of its precursor, 1,5-anhydroglucitol (1,5-AG), a glucose analog present in blood, successfully restored the neutropenia and neutrophil function in G6PC3-deficient and GSD1b patients. The intra-individual variability of response to the treatment and the need to adjust the dose during treatment, especially in pediatric populations, can only be efficiently optimized if the concentration of 1,5-AG in blood is monitored during treatment, together with the patients' clinical signs and symptoms. Monitoring the 1,5-AG levels would be greatly simplified if it could be performed on dry blood spots (DBS) which are easy to collect, store and transport. The challenge is to know if a suitable method can be developed to perform accurate and reproducible assays for 1,5-AG using DBS. Here, we describe and validate an assay that quantifies 1,5-AG in DBS using isotopic dilution quantitation by LC-MS/MS that should greatly facilitate patients' follow-up. 1,5-AG levels measured in plasma and DBS give comparable values. This assay was used to monitor the levels of 1,5-AG in DBS from 3 G6PC3-deficient and 6 GSD1b patients during treatment with SGLT2 inhibitors. We recommend this approach to verify the adequate therapeutical response and compliance to the treatment in G6PC3-deficient and GSD1b patients treated with SGLT2 inhibitors.

Blood glucose trends in glycogen storage disease type Ia: A cross-sectional study.

BACKGROUND: Glycogen storage disease type Ia (GSDIa) is caused by biallelic pathogenic variants in the glucose-6-phosphatase gene (G6PC) and mainly characterized by hypoglycemia, hepatomegaly, and renal insufficiency. Although its symptoms are reportedly mild in patients carrying the G6PC c.648G>T variant, the predominant variant in Japanese patients, details remain unclear. Therefore, we examined continuous glucose monitoring (CGM) data and daily nutritional intake to clarify their associations in Japanese patients with GSDIa with G6PC c.648G>T. METHODS: This cross-sectional study enrolled 32 patients across 10 hospitals. CGM was performed for 14 days, and nutritional intake was recorded using electronic diaries. Patients were divided according to genotype (homozygous/compound heterozygous) and age. The durations of biochemical hypoglycemia and corresponding nutritional intake were analyzed. Multiple regression analysis was performed to identify factors associated with the duration of biochemical hypoglycemia. RESULTS: Data were analyzed for 30 patients. The mean daily duration of hypoglycemia (<4.0 mmol/L) in the homozygous group increased with age (2-11 years [N = 8]: 79.8 min; 12-18 years [5]: 84.8 min; ≥19 years [10]: 131.5 min). No severe hypoglycemic symptoms were recorded in the patients' diaries. The mean frequency of snack intake was approximately three times greater in patients aged 2-11 years (7.1 times/day) than in those aged 12-18 years (1.9 times/day) or ≥19 years (2.2 times/day). Total cholesterol and lactate were independently associated with the duration of biochemical hypoglycemia. CONCLUSION: Although nutritional therapy prevents severe hypoglycemia in patients with GSDIa with G6PC c.648G>T, patients often experience asymptomatic hypoglycemia.

Persistent acidosis and chronic kidney disease in a patient with type 1 glycogen storage disease.

Type 1 glycogen storage disease (GSDI) is a rare autosomal recessive disorder caused by glucose-6-phosphatase (G6Pase) deficiency. We discuss a case of a 29-year-old gentleman who had GSDI with metabolic complications of hypoglycemia, hypertriglyceridemia, hyperuricemia, and short stature. He also suffered from advanced chronic kidney disease, nephrotic range proteinuria, and hepatic adenomas. He presented with acute pneumonia and refractory metabolic acidosis despite treatment with isotonic bicarbonate infusion, reversal of hypoglycemia, and lactic acidosis. He eventually required kidney replacement therapy. The case report highlights the multiple contributing mechanisms and challenges to managing refractory metabolic acidosis in a patient with GSDI. Important considerations for dialysis initiation, decision for long-term dialysis modality and kidney transplantation for patients with GSDI are also discussed in this case report.

Molecular mechanisms of aberrant neutrophil differentiation in glycogen storage disease type Ib.

Glycogen storage disease type Ib (GSD-Ib), characterized by impaired glucose homeostasis, neutropenia, and neutrophil dysfunction, is caused by a deficiency in glucose-6-phosphate transporter (G6PT). Neutropenia in GSD-Ib has been known to result from enhanced apoptosis of neutrophils. However, it has also been raised that neutrophil maturation arrest in the bone marrow would contribute to neutropenia. We now show that G6pt-/- mice exhibit severe neutropenia and impaired neutrophil differentiation in the bone marrow. To investigate the role of G6PT in myeloid progenitor cells, the G6PT gene was mutated using CRISPR/Cas9 system, and single cell-derived G6PT-/- human promyelocyte HL-60 cell lines were established. The G6PT-/- HL-60s exhibited impaired neutrophil differentiation, which is associated with two mechanisms: (i) abnormal lipid metabolism causing a delayed metabolic reprogramming and (ii) reduced nuclear transcriptional activity of peroxisome proliferator-activated receptor-γ (PPARγ) in G6PT-/- HL-60s. In this study, we demonstrated that G6PT is essential for neutrophil differentiation of myeloid progenitor cells and regulates PPARγ activity.

Dapagliflozin Prevents Kidney Glycogen Accumulation and Improves Renal Proximal Tubule Cell Functions in a Mouse Model of Glycogen Storage Disease Type 1b.

BACKGROUND: Mutations in SLC37A4, which encodes the intracellular glucose transporter G6PT, cause the rare glycogen storage disease type 1b (GSD1b). A long-term consequence of GSD1b is kidney failure, which requires KRT. The main protein markers of proximal tubule function, including NaPi2A, NHE3, SGLT2, GLUT2, and AQP1, are downregulated as part of the disease phenotype. METHODS: We utilized an inducible mouse model of GSD1b, TM-G6PT-/-, to show that glycogen accumulation plays a crucial role in altering proximal tubule morphology and function. To limit glucose entry into proximal tubule cells and thus to prevent glycogen accumulation, we administered an SGLT2-inhibitor, dapagliflozin, to TM-G6PT-/- mice. RESULTS: In proximal tubule cells, G6PT suppression stimulates the upregulation and activity of hexokinase-I, which increases availability of the reabsorbed glucose for intracellular metabolism. Dapagliflozin prevented glycogen accumulation and improved kidney morphology by promoting a metabolic switch from glycogen synthesis toward lysis and by restoring expression levels of the main proximal tubule functional markers. CONCLUSION: We provide proof of concept for the efficacy of dapagliflozin in preserving kidney function in GSD1b mice. Our findings could represent the basis for repurposing this drug to treat patients with GSD1b.

A case of glycogen storage disease type â a with gout as the first manifestation. / 以痛风为首发的糖原贮积症â a型一例.

A 24-year-old male was admitted due to recurrent redness, swelling, fever and pain in the ankle, frequently accompanied by hungry feeling. Dual energy CT scans showed multiple small gouty stones in the posterior edge of the bilateral calcaneus and in the space between the bilateral metatarsophalangeal joints. The laboratory examination results indicated hyperlipidemia, high lactate lipids, and low fasting blood glucose. Histopathology of liver biopsy showed significant glycogen accumulation. The results of gene sequencing revealed the compound heterozygous mutations of the G6PC gene c.248G>A (p.Arg83His) and c.238T>A (p.Phe80Ile) in the proband. The c.248G>A mutation was from mother and the c.238T>A mutation was from father. The diagnosis of glycogen storage disease type Ⅰa was confirmed. After giving a high starch diet and limiting monosaccharide intake, as well as receiving uric acid and blood lipids lowering therapy, the condition of the patient was gradually stabilized. After a one-year follow-up, there were no acute episodes of gout and a significant improvement in hungry feeling in the patient.

[Dental rehabilitation in a young patient with glycogen storage disease type 1B]. / Dentale rehabilitatie bij jonge patiënt met glycogeenstapelingsziekte type 1B.

A young woman, known to have glycogen storage disease type 1B (GSD1B) presents with severe periodontitis. GDS1B causes decreased hepatic and renal glucose production and in many cases neutropenia and neutrophil dysfunction leading to recurrent infections. It was decided to treat the patient by extraction of the most affected teeth and retention of the remaining teeth through periodontal treatment, both with antibiotic prophylaxis. After a follow-up period of 1.5 years, during which there was no visible improvement, it was decided to do a full dental extraction and fabricate complete dentures. Due to subsequent bone resorption in both jaws, the dentures were not functional. After consulting the internist and the oral and maxillofacial surgeon, the decision was then made to place dental implants in both the upper and lower jaw for implant-supported prosthetics. After successful treatment and an osseointegration period, the prosthetics were placed. 1 year after placement, there is a stable implantological situation, without pockets or apparent bone loss. The start of SGLT2 medication may have played a significant role in this.

Treating neutropenia and neutrophil dysfunction in glycogen storage disease type Ib with an SGLT2 inhibitor.

Neutropenia and neutrophil dysfunction cause serious infections and inflammatory bowel disease in glycogen storage disease type Ib (GSD-Ib). Our discovery that accumulating 1,5-anhydroglucitol-6-phosphate (1,5AG6P) caused neutropenia in a glucose-6-phosphatase 3 (G6PC3)-deficient mouse model and in 2 rare diseases (GSD-Ib and G6PC3 deficiency) led us to repurpose the widely used antidiabetic drug empagliflozin, an inhibitor of the renal glucose cotransporter sodium glucose cotransporter 2 (SGLT2). Off-label use of empagliflozin in 4 GSD-Ib patients with incomplete response to granulocyte colony-stimulating factor (GCSF) treatment decreased serum 1,5AG and neutrophil 1,5AG6P levels within 1 month. Clinically, symptoms of frequent infections, mucosal lesions, and inflammatory bowel disease resolved, and no symptomatic hypoglycemia was observed. GCSF could be discontinued in 2 patients and tapered by 57% and 81%, respectively, in the other 2. The fluctuating neutrophil numbers in all patients were increased and stabilized. We further demonstrated improved neutrophil function: normal oxidative burst (in 3 of 3 patients tested), corrected protein glycosylation (2 of 2), and normal neutrophil chemotaxis (1 of 1), and bactericidal activity (1 of 1) under treatment. In summary, the glucose-lowering SGLT2 inhibitor empagliflozin, used for type 2 diabetes, was successfully repurposed for treating neutropenia and neutrophil dysfunction in the rare inherited metabolic disorder GSD-Ib without causing symptomatic hypoglycemia. We ascribe this to an improvement in neutrophil function resulting from the reduction of the intracellular concentration of 1,5AG6P.

Studies on glycogen storage disease type 1a animal models: a brief perspective.

Glycogen storage disease type 1 (GSD1) is a rare hereditary monogenic disease characterized by the disturbed glucose metabolism. The most widespread variant of GSD1 is GSD1a, which is a deficiency of glucose-6-phosphatase-ɑ. Glucose-6-phosphatase-ɑ is expressed only in liver, kidney, and intestine, and these organs are primarily affected by its deficiency, and long-term complications of GSD1a include hepatic tumors and chronic liver disease. This article is a brief overview of existing animal models for GSD1a, from the first mouse model of 1996 to modern CRISPR/Cas9-generated ones. First whole-body murine models demonstrated exact metabolic symptoms of GSD1a, but the animals did not survive weaning. The protocol for glucose treatment allowed prolonged survival of affected animals, but long-term complications, such as hepatic tumorigenesis, could not be investigated. Next, organ-specific knockout models were developed, and most of the metabolic research was performed on liver glucose-6-phosphate-deficient mice. Naturally occuring mutation was also discovered in dogs. All these models are widely used to study GSD1a from metabolic and physiological standpoints and to develop possible treatments involving gene therapy. Research performed using these models helped elucidate the role of glycogen and lipid accumulation, hypoxia, mitochondrial dysfunction, and autophagy impairment in long-term complications of GSD1a, including hepatic tumorigenesis. Recently, gene replacement therapy and genome editing were tested on described models, and some of the developed approaches have reached clinical trials.

Untargeted plasma metabolomics identifies broad metabolic perturbations in glycogen storage disease type I.

BACKGROUND: The metabolic defect in glycogen storage disease type I (GSDI) results in fasting hypoglycemia and typical secondary metabolic abnormalities (eg, hypertriglyceridemia, hyperlactatemia, hyperuricemia). The aim of this study was to assess further perturbations of the metabolic network in GSDI patients under ongoing treatment. METHODS: In this prospective observational study, plasma samples of 14 adult patients (11 GSDIa, 3 GSDIb. Mean age 26.4 years, range 16-46 years) on standard treatment were compared to a cohort of 31 healthy controls utilizing ultra-high performance liquid chromatography (UHPLC) in combination with high resolution tandem mass spectrometry (HR-MS/MS) and subsequent statistical multivariate analysis. In addition, plasma fatty acid profiling was performed by GC/EI-MS. RESULTS: The metabolomic profile showed alterations of metabolites in different areas of the metabolic network in both GSD subtypes, including pathways of fuel metabolism and energy generation, lipids and fatty acids, amino acid and methyl-group metabolism, the urea cycle, and purine/pyrimidine metabolism. These alterations were present despite adequate dietary treatment, did not correlate with plasma triglycerides or lactate, both parameters typically used to assess the quality of metabolic control in clinical practice, and were not related to the presence or absence of complications (ie, nephropathy or liver adenomas). CONCLUSION: The metabolic defect of GSDI has profound effects on a variety of metabolic pathways in addition to the known typical abnormalities. These alterations are present despite optimized dietary treatment, which may contribute to the risk of developing long-term complications, an inherent problem of GSDI which appears to be only partly modified by current therapy.

Hepatic Carbohydrate Response Element Binding Protein Activation Limits Nonalcoholic Fatty Liver Disease Development in a Mouse Model for Glycogen Storage Disease Type 1a.

BACKGROUND AND AIMS: Glycogen storage disease (GSD) type 1a is an inborn error of metabolism caused by defective glucose-6-phosphatase catalytic subunit (G6PC) activity. Patients with GSD 1a exhibit severe hepatomegaly due to glycogen and triglyceride (TG) accumulation in the liver. We have shown that the activity of carbohydrate response element binding protein (ChREBP), a key regulator of glycolysis and de novo lipogenesis, is increased in GSD 1a. In the current study, we assessed the contribution of ChREBP to nonalcoholic fatty liver disease (NAFLD) development in a mouse model for hepatic GSD 1a. APPROACH AND RESULTS: Liver-specific G6pc-knockout (L-G6pc-/- ) mice were treated with adeno-associated viruses (AAVs) 2 or 8 directed against short hairpin ChREBP to normalize hepatic ChREBP activity to levels observed in wild-type mice receiving AAV8-scrambled short hairpin RNA (shSCR). Hepatic ChREBP knockdown markedly increased liver weight and hepatocyte size in L-G6pc-/- mice. This was associated with hepatic accumulation of G6P, glycogen, and lipids, whereas the expression of glycolytic and lipogenic genes was reduced. Enzyme activities, flux measurements, hepatic metabolite analysis and very low density lipoprotein (VLDL)-TG secretion assays revealed that hepatic ChREBP knockdown reduced downstream glycolysis and de novo lipogenesis but also strongly suppressed hepatic VLDL lipidation, hence promoting the storage of "old fat." Interestingly, enhanced VLDL-TG secretion in shSCR-treated L-G6pc-/- mice associated with a ChREBP-dependent induction of the VLDL lipidation proteins microsomal TG transfer protein and transmembrane 6 superfamily member 2 (TM6SF2), the latter being confirmed by ChIP-qPCR. CONCLUSIONS: Attenuation of hepatic ChREBP induction in GSD 1a liver aggravates hepatomegaly because of further accumulation of glycogen and lipids as a result of reduced glycolysis and suppressed VLDL-TG secretion. TM6SF2, critical for VLDL formation, was identified as a ChREBP target in mouse liver. Altogether, our data show that enhanced ChREBP activity limits NAFLD development in GSD 1a by balancing hepatic TG production and secretion.

Impaired Very-Low-Density Lipoprotein catabolism links hypoglycemia to hypertriglyceridemia in Glycogen Storage Disease type Ia.

Prevention of hypertriglyceridemia is one of the biomedical targets in Glycogen Storage Disease type Ia (GSD Ia) patients, yet it is unclear how hypoglycemia links to plasma triglyceride (TG) levels. We analyzed whole-body TG metabolism in normoglycemic (fed) and hypoglycemic (fasted) hepatocyte-specific glucose-6-phosphatase deficient (L-G6pc-/- ) mice. De novo fatty acid synthesis contributed substantially to hepatic TG accumulation in normoglycemic L-G6pc-/- mice. In hypoglycemic conditions, enhanced adipose tissue lipolysis was the main driver of liver steatosis, supported by elevated free fatty acid concentrations in GSD Ia mice and GSD Ia patients. Plasma very-low-density lipoprotein (VLDL) levels were increased in GSD Ia patients and in normoglycemic L-G6pc-/- mice, and further elevated in hypoglycemic L-G6pc-/- mice. VLDL-TG secretion rates were doubled in normo- and hypoglycemic L-G6pc-/- mice, while VLDL-TG catabolism was selectively inhibited in hypoglycemic L-G6pc-/- mice. In conclusion, fasting-induced hypoglycemia in L-G6pc-/- mice promotes adipose tissue lipolysis and arrests VLDL catabolism. This mechanism likely contributes to aggravated liver steatosis and dyslipidemia in GSD Ia patients with poor glycemic control and may explain clinical heterogeneity in hypertriglyceridemia between GSD Ia patients.

Emerging roles of autophagy in hepatic tumorigenesis and therapeutic strategies in glycogen storage disease type Ia: A review.

Glycogen storage disease type Ia (GSD-Ia) is an inherited metabolic disease caused by a deficiency in glucose-6-phosphatase-α (G6Pase-α or G6PC) which plays a critical role in blood glucose homeostasis by catalyzing the hydrolysis of glucose-6-phosphate (G6P) to glucose and phosphate in the terminal step of glycogenolysis and gluconeogenesis. Patients with GSD-Ia manifest life-threatening fasting hypoglycemia along with the excessive accumulation of hepatic glycogen and triglycerides which results in hepatomegaly and a risk of long-term complications such as hepatocellular adenoma and carcinoma (HCA/HCC). The etiology of HCA/HCC development in GSD-Ia, however, is unknown. Recent studies have shown that the livers in model animals of GSD-Ia display impairment of autophagy, a cellular recycling process which is critical for energy metabolism and cellular homeostasis. However, molecular mechanisms of autophagy impairment and its involvement in pathogenesis in GSD-Ia are still under investigation. Here, we summarize the latest advances for signaling pathways implicated in hepatic autophagy impairment and the roles of autophagy in hepatic tumorigenesis in GSD-Ia. In addition, recent evidence has illustrated that autophagy plays an important role in hepatic metabolism and liver-directed gene therapy mediated by recombinant adeno-associated virus (rAAV). Therefore, we highlight the possible role of hepatic autophagy in metabolic control and rAAV-mediated gene therapy for GSD-Ia. In this review, we also provide potential therapeutic strategies for GSD-Ia on the basis of molecular mechanisms underlying hepatic autophagy impairment in GSD-Ia.