Type I glycogen storage diseases: disorders of the glucose-6-phosphatase/glucose-6-phosphate transporter complexes

Liver-Directed Gene Therapy Mitigates Early Nephropathy in Murine Glycogen Storage Disease Type Ia

Nephropathy is a complication of glycogen storage disease type Ia (GSD-Ia), a metabolic disorder caused by pathogenic variants in glucose-6-phosphatase-α (G6Pase-α or G6PC1). While maintaining blood glucose homeostasis can delay the progression of renal disease in GSD-Ia, the benefits of liver-directed G6PC1 gene therapy on nephropathy remain unclear. This study evaluates the effects of low- and high-dose G6PC1 liver gene augmentation therapy on kidney function. The G6pc-/- mice, which lack G6Pase-α activity in both liver and kidney, were treated with G6PC1 gene therapy to restore either low or near-normal levels of liver G6Pase-α activity, and renal phenotype was examined at age 12 weeks. Both groups exhibited impaired renal glucose homeostasis, altered renal glucose reabsorption, acute kidney injury, and early signs of renal fibrosis. However, mice with near-normal liver G6Pase-α activity had better renal glucose reabsorption and homeostasis with lower serum levels of cystatin C and blood urea nitrogen, key markers of kidney function. These findings highlight the potential of liver-directed G6PC1 gene therapy to enhance metabolic control and mitigate early kidney disease in GSD-Ia.

Lactylation-driven ALKBH5 diminishes macrophage NLRP3 inflammasome activation in patients with G6PT deficiency

BACKGROUND

Neutropenia represents an important clinical problem in patients with glycogen storage disease type Ib, characterized by genetic deficiency in glucose-6-phosphate translocase (G6PT/SLC37A4). However, the role of G6PT in macrophages has not been elucidated.

OBJECTIVE

We sought to investigate the function of G6PT in macrophage inflammation.

METHODS

Functional assays (including immunoblotting, real-time quantitative PCR, flow cytometry, immunofluorescence staining, and enzyme-linked immunosorbent assay) and RNA sequencing were performed.

RESULTS

We find that macrophages from patients deficient in G6PT exhibited diminished NLRP3 inflammasome activation. Mechanistically, deficiency of G6PT promotes glycolysis and lactate production in macrophages. Lactate accumulation potently induces ALKBH5 upregulation via H3K18 lactylation. ALKBH5 decreases m6A modification on NLRP3 messenger RNA, attenuating its transcript stability and thus inhibiting inflammasome activation. Further, treating G6PT-deficient macrophages with an inhibitor of the lactate dehydrogenase to lower their lactate levels restores NLRP3 inflammasome activation and rescues bacterial handling defect.

CONCLUSION

These findings reveal a previously unknown pathogenic mechanism of lactylation-driven defective NLRP3 inflammasome signaling and subsequent impaired antimicrobial activity as driving factors in these inflammatory disorders, indicating that glycolysis/lactate/histone lactylation cascade may be a potential therapeutic target for glycogen storage disease type Ib.

Biochemical characterization of the human ubiquitous glucose-6-phosphatase in neutrophil granulocytes

Glucose-6-phosphatase-β (G6PC3) is a ubiquitous phosphatase present in the endoplasmic reticulum, which, unlike G6PC1, is not responsible for maintaining blood glucose level under starvation. Recently, G6PC3 has been shown to play an important role in neutrophil granulocytes, eliminating the toxic metabolite 1,5-anhydroglucitol-6-phosphate. The present study aimed to look for alternative substrates for the enzyme and outline the expression changes in the parts of this multicomponent system during neutrophil granulocyte differentiation. We determined the kinetic characteristics of recombinant human G6PC3 towards different sugar phosphates, and the transport of these compounds was also measured in rat liver microsomes. We found that all investigated sugar phosphates are substrates for G6PC3, although their microsomal transport is much slower than that of glucose-6-phosphate. Using the HL-60 promyelocytic leukemia cell line as an in vitro model system for myeloid differentiation, we found no significant differences in enzyme expression and phosphatase activity latency between undifferentiated and differentiated cells. Our results provide novel insights into the possible role of G6PC3 in the dephosphorylation of alternative sugar phosphates or their metabolites synthesized in the endoplasmic reticulum and confirm the potential feature of the enzyme in the promyelocytic stage as well. These findings contribute to our knowledge of intracellular carbohydrate metabolism of neutrophil granulocytes, which facilitates further research directions to better understand the underlying mechanisms of neutropenias.

Characterization and Proteomic Profiling of Hepatocyte-like Cells Derived from Human Wharton's Jelly Mesenchymal Stromal Cells: De Novo Expression of Liver-Specific Enzymes

End-stage liver disease (ESLD), affecting millions worldwide, represents a challenging issue for clinical research and global public health. Liver transplantation is the gold standard therapeutic approach but shows some drawbacks. Hepatocyte transplantation could be a reliable alternative for patient treatment. Mesenchymal stromal cells derived from Wharton's jelly of the umbilical cord (WJ-MSCs) can differentiate into hepatocyte-like cells (HLCs) and show immunomodulatory functions. Due to the increasing demand for fully characterized cell therapy vehicles warranting both the safety and efficacy of treatments, in this work, we extensively characterized WJ-MSCs before and after the application of a hepatocyte-directed differentiation protocol. HLCs exhibited a morphology resembling that of hepatocytes, expressed early and late hepatic markers (α-fetoprotein, albumin, CK18, HNF4-α), and acquired hepatic functions (glycogen synthesis, xenobiotics detoxification), as also revealed by the shotgun proteomics approach. HLCs maintained the same pattern of immunomodulatory molecule expression and mesenchymal markers, other than displaying specific enzymes, suggesting these cells as promising candidates for cellular therapy of ESLD. Our work shed new light on the basic biology of HLCs, suggesting new therapeutic approaches to treat ESLD.

Phenylbutyric Acid Modulates Apoptosis and ER Stress-Related Gene Expression in Glycogen Storage Disease Type Ib In Vitro Model

INTRODUCTION

Chronic endoplasmic reticulum (ER) stress and increased apoptosis are involved in the pathogenesis of glycogen storage disease Ib (GSD Ib), whereas small molecule phenylbutyrate (4-PBA) showed the capability of reducing ER stress-induced apoptosis. The objective was to generate an in vitro system in which capability of small molecules (SMs) to influence ER stress and apoptosis could be screened at the expression level.

METHODS

G6PT-deficient FlpInHEK293 cell line was created and validated using the CRISPR/Cas9 knockout method. Molecular markers of unfolded protein response (ATF4, DDIT3, HSPA5, XBP1s), and apoptosis (BCL2/BAX, CASP3, CASP7) in G6PT-deficient cells were analyzed using RT-qPCR method before and upon the treatment with 4-PBA.

RESULTS

Treatment with the most effective dose of 1 mM 4-PBA reduced the expression of UPR markers and executioner caspases, while increased BCL2/BAX ratio in G6PT-deficient cells. Our results proved the concept that 4-PBA could alleviate markers of ER stress detected in the GSD Ib in vitro model system and prevent cell death.

CONCLUSION

This cost-effective in vitro model screens the therapeutic potential of SMs affecting ER stress and apoptosis in G6PT-deficient kidney cells, offering a first-line screening assay for promising compounds. 4-PBA's potential repurposing for GSD Ib patients opens new research directions.

Base-editing corrects metabolic abnormalities in a humanized mouse model for glycogen storage disease type-Ia

Glycogen storage disease type-Ia patients, deficient in the G6PC1 gene encoding glucose-6-phosphatase-α, lack blood glucose control, resulting in life-threatening hypoglycemia. Here we show our humanized mouse model, huR83C, carrying the pathogenic G6PC1-R83C variant displays the phenotype of glycogen storage disease type-Ia and dies prematurely. We evaluate the efficacy of BEAM-301, a formulation of lipid nanoparticles containing a newly-engineered adenine base editor, to correct the G6PC1-R83C variant in huR83C mice and monitor phenotypic correction through one year. BEAM-301 can correct up to ~60% of the G6PC1-R83C variant in liver cells, restores blood glucose control, improves metabolic abnormalities of the disease, and confers long-term survival to the mice. Interestingly, just ~10% base correction is therapeutic. The durable pharmacological efficacy of base editing in huR83C mice supports the development of BEAM-301 as a potential therapeutic for homozygous and compound heterozygous glycogen storage disease type-Ia patients carrying the G6PC1-R83C variant.

A large cohort from an immunology reference center and an algorithm for the follow-up of chronic neutropenia

Chronic neutropenia causes involve nutritional deficiencies and inborn errors of immunity(IEI), such as severe congenital neutropenia. To classify common chronic neutropenia causes in a pediatric immunology unit. We enrolled 109 chronic neutropenia patients admitted to a pediatric immunology department between 2002-2022. We recorded clinical/laboratory features and genetic characteristics. The male/female ratio was 63/46. Fifty-eight patients had parental consanguinity(57.4%). 26.6% (n = 29) patients had at least one individual in their family with neutropenia. Common symtpoms at presentation were upper respiratory tract infections(URTI)(31.1%), oral aphthae(23.6%), skin infections(23.6%), pneumonia(20.8%), and recurrent abscesses(12.3%). Common infections during follow-up were URTI(56.8%), pneumonia(33%), skin infections(25.6%), gastroenteritis(18.3%), and recurrent abscesses(14,6%). Common long-term complications were dental problems(n = 51), osteoporosis(n = 22), growth retardation(n = 14), malignancy(n = 16)[myelodysplastic syndrome(n = 10), large granulocytic leukemia(n = 1), acute lymphoblastic leukemia(n = 1), Hodgkin lymphoma(n = 1), EBV-related lymphoma(n = 1), leiomyosarcoma(n = 1), and thyroid neoplasm(n = 1)]. We performed a genetic study in 86 patients, and 69(71%) got a genetic diagnosis. Common gene defects were HAX-1(n = 26), ELA-2 (ELANE)(n = 10), AP3B1(n = 4), and ADA-2(n = 4) gene defects. The IEI ratio(70.6%) was high. GCSF treatment(93.4%), immunoglobulin replacement therapy(18.7%), and HSCT(15.9%) were the treatment options. The mortality rate was 12.9%(n = 14). The most common long term complications were dental problems that is three times more common in patients with known genetic mutations. We prepared an algorithm for chronic neutropenia depending on the present cohort. An important rate of inborn errors of immunity, especially combined immunodeficiency(11.9%) was presented in addition to congenital phagocytic cell defects. Early diagnosis will allow us tailor the disease-specific treatment options sooner, preventing irreversible consequences.

Neutrophil functions in patients with neutropenia due to glycogen storage disease type 1b treated with empagliflozin

ABSTRACT

Neutropenia and neutrophil dysfunction in glycogen storage disease type 1b (GSD1b) are caused by the accumulation of 1,5-anhydroglucitol-6-phosphate in granulocytes. The antidiabetic drug empagliflozin reduces the concentration of 1,5-anhydroglucitol (1,5-AG), thus restoring neutrophil counts and functions, leading to promising results in previous case reports. Here, we present a comprehensive analysis of neutrophil function in 7 patients with GSD1b and 11 healthy donors, aiming to evaluate the immediate (after 3 months) and long-term (after 12 months) efficacy of empagliflozin compared with the reference treatment with granulocyte-colony stimulating factor (G-CSF). We found that most patients receiving G-CSF remained neutropenic with dysfunctional granulocytes, whereas treatment with empagliflozin increased neutrophil counts and improved functionality by inhibiting apoptosis, restoring phagocytosis and the chemotactic response, normalizing the oxidative burst, and stabilizing cellular and plasma levels of defensins and lactotransferrin. These improvements correlated with the decrease in serum 1,5-AG levels. However, neither G-CSF nor empagliflozin overcame deficiencies in the production of cathelicidin/LL-37 and neutrophil extracellular traps. Given the general improvement promoted by empagliflozin treatment, patients were less susceptible to severe infections. G-CSF injections were therefore discontinued in 6 patients (and the dose was reduced in the seventh) without adverse effects. Our systematic analysis, the most extensive reported thus far, has demonstrated the superior efficacy of empagliflozin compared with G-CSF, restoring the neutrophil population and normal immune functions. This trial was registered as EudraCT 2021-000580-78.

Tanycytes release glucose using the glucose-6-phosphatase system during hypoglycemia to control hypothalamic energy balance

OBJECTIVE

The liver releases glucose into the blood using the glucose-6-phosphatase (G6Pase) system, a multiprotein complex located in the endoplasmic reticulum (ER). Here, we show for the first time that the G6Pase system is also expressed in hypothalamic tanycytes, and it is required to regulate energy balance.

METHODS

Using automatized qRT-PCR and immunohistochemical analyses, we evaluated the expression of the G6Pase system. Fluorescent glucose analogue (2-NBDG) uptake was evaluated by 4D live-cell microscopy. Glucose release was tested using a glucose detection kit and high-content live-cell analysis instrument, Incucyte s3. In vivo G6pt knockdown in tanycytes was performed by AAV1-shG6PT-mCherry intracerebroventricular injection. Body weight gain, adipose tissue weight, food intake, glucose metabolism, c-Fos, and neuropeptide expression were evaluated at 4 weeks post-transduction.

RESULTS

Tanycytes sequester glucose-6-phosphate (G6P) into the ER through the G6Pase system and release glucose in hypoglycaemia via facilitative glucose transporters (GLUTs). Strikingly, in vivo tanycytic G6pt knockdown has a powerful peripheral anabolic effect observed through decreased body weight, white adipose tissue (WAT) tissue mass, and strong downregulation of lipogenesis genes. Selective deletion of G6pt in tanycytes also decreases food intake, c-Fos expression in the arcuate nucleus (ARC), and Npy mRNA expression in fasted mice.

CONCLUSIONS

The tanycyte-associated G6Pase system is a central mechanism involved in controlling metabolism and energy balance.

A case study of a liver transplant-treated patient with glycogen storage disease type Ia presenting with multiple inflammatory hepatic adenomas: an analysis of clinicopathologic and genetic data

BACKGROUND

Glycogen storage disease (GSD) is a disease caused by excessive deposition of glycogen in tissues due to genetic disorders in glycogen metabolism. Glycogen storage disease type I (GSD-I) is also known as VonGeirk disease and glucose-6-phosphatase deficiency. This disease is inherited in an autosomal recessive manner, and both sexes can be affected. The main symptoms include hypoglycaemia, hepatomegaly, acidosis, hyperlipidaemia, hyperuricaemia, hyperlactataemia, coagulopathy and developmental delay.

CASE PRESENTATION

Here, we present the case of a 13-year-old female patient with GSD Ia complicated with multiple inflammatory hepatic adenomas. She presented to the hospital with hepatomegaly, hypoglycaemia, and epistaxis. By clinical manifestations and imaging and laboratory examinations, we suspected that the patient suffered from GSD I. Finally, the diagnosis was confirmed by liver pathology and whole-exome sequencing (WES). WES revealed a synonymous mutation, c.648 G > T (p.L216 = , NM_000151.4), in exon 5 and a frameshift mutation, c.262delG (p.Val88Phefs*14, NM_000151.4), in exon 2 of the G6PC gene. According to the pedigree analysis results of first-generation sequencing, heterozygous mutations of c.648 G > T and c.262delG were obtained from the patient's father and mother. Liver pathology revealed that the solid nodules were hepatocellular hyperplastic lesions, and immunohistochemical (IHC) results revealed positive expression of CD34 (incomplete vascularization), liver fatty acid binding protein (L-FABP) and C-reactive protein (CRP) in nodule hepatocytes and negative expression of β-catenin and glutamine synthetase (GS). These findings suggest multiple inflammatory hepatocellular adenomas. PAS-stained peripheral hepatocytes that were mostly digested by PAS-D were strongly positive. This patient was finally diagnosed with GSD-Ia complicated with multiple inflammatory hepatic adenomas, briefly treated with nutritional therapy after diagnosis and then underwent living-donor liver allotransplantation. After 14 months of follow-up, the patient recovered well, liver function and blood glucose levels remained normal, and no complications occurred.

CONCLUSION

The patient was diagnosed with GSD-Ia combined with multiple inflammatory hepatic adenomas and received liver transplant treatment. For childhood patients who present with hepatomegaly, growth retardation, and laboratory test abnormalities, including hypoglycaemia, hyperuricaemia, and hyperlipidaemia, a diagnosis of GSD should be considered. Gene sequencing and liver pathology play important roles in the diagnosis and typing of GSD.

Empagliflozin in children with glycogen storage disease-associated inflammatory bowel disease: a prospective, single-arm, open-label clinical trial

Glycogen storage disease type Ib (GSD-Ib) is a rare inborn error of glycogen metabolism caused by mutations in SLC37A4. Patients with GSD-Ib are at high risk of developing inflammatory bowel disease (IBD). We evaluated the efficacy of empagliflozin, a renal sodium‒glucose cotransporter protein 2 (SGLT2) inhibitor, on colonic mucosal healing in patients with GSD-associated IBD. A prospective, single-arm, open-label clinical trial enrolled eight patients with GSD-associated IBD from Guangdong Provincial People's Hospital in China from July 1, 2022 through December 31, 2023. Eight patients were enrolled with a mean age of 10.34 ± 2.61 years. Four male and four female. The endoscopic features included deep and large circular ulcers, inflammatory hyperplasia, obstruction and stenosis. The SES-CD score significantly decreased at week 48 compared with before empagliflozin. Six patients completed 48 weeks of empagliflozin therapy and endoscopy showed significant improvement or healing of mucosal ulcers, inflammatory hyperplasia, stenosis, and obstruction. One patient had severe sweating that required rehydration and developed a urinary tract infection. No serious or life-threatening adverse events. This study suggested that empagliflozin may promote colonic mucosal healing and reduce hyperplasia, stenosis, and obstruction in children with GSD-associated IBD.

Integrative analysis of pathogenic variants in glucose-6-phosphatase based on an AlphaFold2 model

Mediating the terminal reaction of gluconeogenesis and glycogenolysis, the integral membrane protein glucose-6-phosphate catalytic subunit 1 (G6PC1) regulates hepatic glucose production by catalyzing hydrolysis of glucose-6-phosphate (G6P) within the lumen of the endoplasmic reticulum. Consistent with its vital contribution to glucose homeostasis, inactivating mutations in G6PC1 causes glycogen storage disease (GSD) type 1a characterized by hepatomegaly and severe hypoglycemia. Despite its physiological importance, the structural basis of G6P binding to G6PC1 and the molecular disruptions induced by missense mutations within the active site that give rise to GSD type 1a are unknown. In this study, we determine the atomic interactions governing G6P binding as well as explore the perturbations imposed by disease-linked missense variants by subjecting an AlphaFold2 G6PC1 structural model to molecular dynamics simulations and in silico predictions of thermodynamic stability validated with robust in vitro and in situ biochemical assays. We identify a collection of side chains, including conserved residues from the signature phosphatidic acid phosphatase motif, that contribute to a hydrogen bonding and van der Waals network stabilizing G6P in the active site. The introduction of GSD type 1a mutations modified the thermodynamic landscape, altered side chain packing and substrate-binding interactions, and induced trapping of catalytic intermediates. Our results, which corroborate the high quality of the AF2 model as a guide for experimental design and to interpret outcomes, not only confirm the active-site structural organization but also identify previously unobserved mechanistic contributions of catalytic and noncatalytic side chains.

Inhibition of Wnt/β-catenin signaling reduces renal fibrosis in murine glycogen storage disease type Ia

Glycogen storage disease type Ia (GSD-Ia) is caused by a deficiency in the enzyme glucose-6-phosphatase-α (G6Pase-α or G6PC) that is expressed primarily in the gluconeogenic organs, namely liver, kidney cortex, and intestine. Renal G6Pase-α deficiency in GSD-Ia is characterized by impaired gluconeogenesis, nephromegaly due to elevated glycogen accumulation, and nephropathy caused, in part, by renal fibrosis, mediated by activation of the renin-angiotensin system (RAS). The Wnt/β-catenin signaling regulates the expression of a variety of downstream mediators implicated in renal fibrosis, including multiple genes in the RAS. Sustained activation of Wnt/β-catenin signaling is associated with the development and progression of renal fibrotic lesions that can lead to chronic kidney disease. In this study, we examined the molecular mechanism underlying GSD-Ia nephropathy. Damage to the kidney proximal tubules is known to trigger acute kidney injury (AKI) that can, in turn, activate Wnt/β-catenin signaling. We show that GSD-Ia mice have AKI that leads to activation of the Wnt/β-catenin/RAS axis. Renal fibrosis was demonstrated by increased renal levels of Snail1, α-smooth muscle actin (α-SMA), and extracellular matrix proteins, including collagen-Iα1 and collagen-IV. Treating GSD-Ia mice with a CBP/β-catenin inhibitor, ICG-001, significantly decreased nuclear translocated active β-catenin and reduced renal levels of renin, Snail1, α-SMA, and collagen-IV. The results suggest that inhibition of Wnt/β-catenin signaling may be a promising therapeutic strategy for GSD-Ia nephropathy.

Lipid Nanoparticles Optimized for Targeting and Release of Nucleic Acid

Lipid nanoparticles (LNPs) are currently the most promising clinical nucleic acids drug delivery vehicles. LNPs prevent the degradation of cargo nucleic acids during blood circulation. Upon entry into the cell, specific components of the lipid nanoparticles can promote the endosomal escape of nucleic acids. These are the basic properties of lipid nanoparticles as nucleic acid carriers. As LNPs exhibit hepatic aggregation characteristics, enhancing targeting out of the liver is a crucial way to improve LNPs administrated in vivo. Meanwhile, endosomal escape of nucleic acids loaded in LNPs is often considered inadequate, and therefore, much effort is devoted to enhancing the intracellular release efficiency of nucleic acids. Here, different strategies to efficiently deliver nucleic acid delivery from LNPs are concluded and their mechanisms are investigated. In addition, based on the information on LNPs that are in clinical trials or have completed clinical trials, the issues that are necessary to be approached in the clinical translation of LNPs are discussed, which it is hoped will shed light on the development of LNP nucleic acid drugs.

Severe perioperative lactic acidosis in a pediatric patient with glycogen storage disease type Ia: a case report

BACKGROUND

Glycogen storage disease (GSD) is a group of rare inherited metabolic disorders caused by enzyme deficiencies in glycogen catabolism. GSD type Ia is a congenital deficiency of the enzyme responsible for the final step in glucose production by glycolysis, resulting in impaired carbohydrate metabolism.

CASE PRESENTATION

A 14-year-old boy with GSD type Ia was scheduled for a maxillary cystectomy under general anesthesia. He was taking oral sugars such as uncooked cornstarch regularly to prevent hypoglycemia. Perioperatively, glucose was administered via the peripheral vein for fasting; however, severe lactic acidosis occurred. He also developed hypercapnia because of intraoperative poor ventilation caused by hepatomegaly.

CONCLUSIONS

We experienced a child with GSD type Ia who developed severe lactic acidosis despite continuous glucose infusion. Further studies are required to determine appropriate perioperative management for patients with GSD, including fasting glucose administration.

Three novel SLC37A4 variants in glycogen storage disease type 1b and a literature review

Glycogen storage disease type 1b (GSD1b) is a rare genetic disorder, resulting from mutations in the SLC37A4 gene located on chromosome 11q23.3. Although the SLC37A4 gene has been identified as the pathogenic gene for GSD1b, the complete variant spectrum of this gene remains to be fully elucidated. In this study, we present three patients diagnosed with GSD1b through genetic testing. We detected five variants of the SLC37A4 gene in these three patients, with three of these mutations (p. L382Pfs*15, p. G117fs*28, and p. T312Sfs*13) being novel variants not previously reported in the literature. We also present a literature review and general overview of the currently reported SLC37A4 gene variants. Our study expands the mutation spectrum of SLC37A4, which may help enable genetic testing to facilitate prompt diagnosis, appropriate intervention, and genetic counseling for affected families.

A molecular signature for the G6PC3/SLC37A2/SLC37A4 interactors in glioblastoma disease progression and in the acquisition of a brain cancer stem cell phenotype

BACKGROUND

Glycogen plays an important role in glucose homeostasis and contributes to key functions related to brain cancer cell survival in glioblastoma multiforme (GBM) disease progression. Such adaptive molecular mechanism is dependent on the glycogenolytic pathway and intracellular glucose-6-phosphate (G6P) sensing by brain cancer cells residing within those highly hypoxic tumors. The involvement of components of the glucose-6-phosphatase (G6Pase) system remains however elusive.

OBJECTIVE

We questioned the gene expression levels of components of the G6Pase system in GBM tissues and their functional impact in the control of the invasive and brain cancer stem cells (CSC) phenotypes.

METHODS

In silico analysis of transcript levels in GBM tumor tissues was done by GEPIA. Total RNA was extracted and gene expression of G6PC1-3 as well as of SLC37A1-4 members analyzed by qPCR in four human brain cancer cell lines and from clinically annotated brain tumor cDNA arrays. Transient siRNA-mediated gene silencing was used to assess the impact of TGF-β-induced epithelial-to-mesenchymal transition (EMT) and cell chemotaxis. Three-dimensional (3D) neurosphere cultures were generated to recapitulate the brain CSC phenotype.

RESULTS

Higher expression in G6PC3, SLC37A2, and SLC37A4 was found in GBM tumor tissues in comparison to low-grade glioma and healthy tissue. The expression of these genes was also found elevated in established human U87, U251, U118, and U138 GBM cell models compared to human HepG2 hepatoma cells. SLC37A4/G6PC3, but not SLC37A2, levels were induced in 3D CD133/SOX2-positive U87 neurospheres when compared to 2D monolayers. Silencing of SLC37A4/G6PC3 altered TGF-β-induced EMT biomarker SNAIL and cell chemotaxis.

CONCLUSION

Two members of the G6Pase system, G6PC3 and SLC37A4, associate with GBM disease progression and regulate the metabolic reprogramming of an invasive and CSC phenotype. Such molecular signature may support their role in cancer cell survival and chemoresistance and become future therapeutic targets.

CRISPR/Cas9-based double-strand oligonucleotide insertion strategy corrects metabolic abnormalities in murine glycogen storage disease type-Ia

Glycogen storage disease type-Ia (GSD-Ia), characterized by impaired blood glucose homeostasis, is caused by a deficiency in glucose-6-phosphatase-α (G6Pase-α or G6PC). Using the G6pc-R83C mouse model of GSD-Ia, we explored a CRISPR/Cas9-based double-strand DNA oligonucleotide (dsODN) insertional strategy that uses the nonhomologous end-joining repair mechanism to correct the pathogenic p.R83C variant in G6pc exon-2. The strategy is based on the insertion of a short dsODN into G6pc exon-2 to disrupt the native exon and to introduce an additional splice acceptor site and the correcting sequence. When transcribed and spliced, the edited gene would generate a wild-type mRNA encoding the native G6Pase-α protein. The editing reagents formulated in lipid nanoparticles (LNPs) were delivered to the liver. Mice were treated either with one dose of LNP-dsODN at age 4 weeks or with two doses of LNP-dsODN at age 2 and 4 weeks. The G6pc-R83C mice receiving successful editing expressed ~4% of normal hepatic G6Pase-α activity, maintained glucose homeostasis, lacked hypoglycemic seizures, and displayed normalized blood metabolite profile. The outcomes are consistent with preclinical studies supporting previous gene augmentation therapy which is currently in clinical trials. This editing strategy may offer the basis for a therapeutic approach with an earlier clinical intervention than gene augmentation, with the additional benefit of a potentially permanent correction of the GSD-Ia phenotype.

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.

Molecular mechanisms of catalytic inhibition for active site mutations in glucose-6-phosphatase catalytic subunit 1 linked to glycogen storage disease

Mediating the terminal reaction of gluconeogenesis and glycogenolysis, the integral membrane protein G6PC1 regulates hepatic glucose production by catalyzing hydrolysis of glucose-6-phosphate (G6P) within the lumen of the endoplasmic reticulum. Consistent with its vital contribution to glucose homeostasis, inactivating mutations in G6PC1 cause glycogen storage disease (GSD) type 1a characterized by hepatomegaly and severe hypoglycemia. Despite its physiological importance, the structural basis of G6P binding to G6PC1 and the molecular disruptions induced by missense mutations within the active site that give rise to GSD type 1a are unknown. Exploiting a computational model of G6PC1 derived from the groundbreaking structure prediction algorithm AlphaFold2 (AF2), we combine molecular dynamics (MD) simulations and computational predictions of thermodynamic stability with a robust in vitro screening platform to define the atomic interactions governing G6P binding as well as explore the energetic perturbations imposed by disease-linked variants. We identify a collection of side chains, including conserved residues from the signature phosphatidic acid phosphatase motif, that contribute to a hydrogen bonding and van der Waals network stabilizing G6P in the active site. Introduction of GSD type 1a mutations into the G6PC1 sequence elicits changes in G6P binding energy, thermostability and structural properties, suggesting multiple pathways of catalytic impairment. Our results, which corroborate the high quality of the AF2 model as a guide for experimental design and to interpret outcomes, not only confirm active site structural organization but also suggest novel mechanistic contributions of catalytic and non-catalytic side chains.

Glycogen storage diseases: An update

Glycogen storage diseases (GSDs), also referred to as glycogenoses, are inherited metabolic disorders of glycogen metabolism caused by deficiency of enzymes or transporters involved in the synthesis or degradation of glycogen leading to aberrant storage and/or utilization. The overall estimated GSD incidence is 1 case per 20000-43000 live births. There are over 20 types of GSD including the subtypes. This heterogeneous group of rare diseases represents inborn errors of carbohydrate metabolism and are classified based on the deficient enzyme and affected tissues. GSDs primarily affect liver or muscle or both as glycogen is particularly abundant in these tissues. However, besides liver and skeletal muscle, depending on the affected enzyme and its expression in various tissues, multiorgan involvement including heart, kidney and/or brain may be seen. Although GSDs share similar clinical features to some extent, there is a wide spectrum of clinical phenotypes. Currently, the goal of treatment is to maintain glucose homeostasis by dietary management and the use of uncooked cornstarch. In addition to nutritional interventions, pharmacological treatment, physical and supportive therapies, enzyme replacement therapy (ERT) and organ transplantation are other treatment approaches for both disease manifestations and long-term complications. The lack of a specific therapy for GSDs has prompted efforts to develop new treatment strategies like gene therapy. Since early diagnosis and aggressive treatment are related to better prognosis, physicians should be aware of these conditions and include GSDs in the differential diagnosis of patients with relevant manifestations including fasting hypoglycemia, hepatomegaly, hypertransaminasemia, hyperlipidemia, exercise intolerance, muscle cramps/pain, rhabdomyolysis, and muscle weakness. Here, we aim to provide a comprehensive review of GSDs. This review provides general characteristics of all types of GSDs with a focus on those with liver involvement.

Elucidation of intermolecular interactions between chlorogenic acid and glucose-6-phosphate translocase: A step towards chemically induced glycogen storage disease type 1b model

Glucose-6-phosphate translocase enzyme, encoded by SLC37A4 gene, is a crucial enzyme involved in transporting glucose-6-phosphate into the endoplasmic reticulum. Inhibition of this enzyme can cause Von-Gierke's/glycogen storage disease sub-type 1b. The current study dealt to elucidate the intermolecular interactions to assess the inhibitory activity of Chlorogenic acid (CGA) against SLC37A4 was assessed by molecular docking and dynamic simulation. The alpha folded model of SLC37A4 and CGA 3D structure were optimized using CHARMM force field, using energy minimization protocol in the Discovery Studio software. Glucose-6-phosphate (G6P) and CGA molecular docking, Molecular dynamics (MD) simulation, analysis of binding free energy of G6P-SLC37A4 and CGA-SLC37A4 complexes was performed for 100 ns using GROMACS, followed by principal component analysis (PCA). The docking score of the CGA-SLC37A4 complex exhibited a higher docking score (- 8.2 kcal/mol) when compared to the G6P-SLC37A4 complex (- 6.5 kcal/mol), suggesting a stronger binding interaction between CGA and SLC37A4. Further, the MD simulation demonstrated a stable backbone and complex Root Mean Square Deviation (RMSD), the least RMS fluctuation, and stable active site residue interactions throughout the 100 ns production run. The CGA complex with SLC37A4 exhibits higher compactness and formed 8 hydrogen bonds to achieve stability. The binding free energy of the G6P-SLC37A4 and CGA-SLC37A4 complex was found to be - 12.73 and - 31.493 kcal/mol. Lys29 formed stable contact for both G6P (- 4.73 kJ/mol) and SLC37A4 (- 2.18 kJ/mol). This study imparts structural insights into the competitive inhibition of SLC37A4 by CGA. CGA shows potential as a candidate to induce manifestations of GSD1b by inhibiting glycogenolysis, and gluconeogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03661-5.

Identification of mutations that causes glucose-6-phosphate transporter defect in tunisian patients with glycogenosis type 1b

BACKGROUND

Glycogen storage disease type 1b (GSD1b) is an autosomal recessive lysosomal storage disease caused by defective glucose-6-phosphate transporter encoded by SLC37A4 leading to the accumulation of glycogen in various tissues. The high rate of consanguineous marriages in Tunisian population provides an ideal environment to facilitate the identification of homozygous pathogenic mutations. We aimed to determine the clinical and genetic profiles of patients with GSD1b to evaluate SLC37A4 mutations spectrum in Tunisian patients.

METHODS

All exons and flanking intron regions of SLC37A4 gene were screened by direct sequencing to identify mutations and polymorphisms in three unrelated families with GSD1b. Bioinformatics tools were then used to predict the impacts of identified mutations on the structure and function of protein in order to propose a function-structure relationship of the G6PT1 protein.

RESULTS

Three patients (MT, MB and SI) in Families I, II and III who had the severe phenotype were homoallelic for the two identified mutations: p.R300H (famillies I, II) and p.W393X (Family III), respectively. One of the alterations was a missense mutation p.R300H of exon 6 in SLC37A4 gene. The analysis of the protein structure flexibility upon p.R300H mutation using DynaMut tool and CABS-flex 2.0 server showed that the reported mutation increase the molecule flexibility of in the cytosol region and would probably lead to significant conformational changes.

CONCLUSION

This is the first Tunisian report of SLC37A4 mutations identified in Tunisia causing the glycogenosis type Ib disease. Bioinformatics analysis allowed us to establish an approximate structure-function relationship for the G6PT1 protein, thereby providing better genotype/phenotype correlation knowledge.

Normalization of hepatic ChREBP activity does not protect against liver disease progression in a mouse model for Glycogen Storage Disease type Ia

BACKGROUND

Glycogen storage disease type 1a (GSD Ia) is an inborn error of metabolism caused by a defect in glucose-6-phosphatase (G6PC1) activity, which induces severe hepatomegaly and increases the risk for liver cancer. Hepatic GSD Ia is characterized by constitutive activation of Carbohydrate Response Element Binding Protein (ChREBP), a glucose-sensitive transcription factor. Previously, we showed that ChREBP activation limits non-alcoholic fatty liver disease (NAFLD) in hepatic GSD Ia. As ChREBP has been proposed as a pro-oncogenic molecular switch that supports tumour progression, we hypothesized that ChREBP normalization protects against liver disease progression in hepatic GSD Ia.

METHODS

Hepatocyte-specific G6pc knockout (L-G6pc-/-) mice were treated with AAV-shChREBP to normalize hepatic ChREBP activity.

RESULTS

Hepatic ChREBP normalization in GSD Ia mice induced dysplastic liver growth, massively increased hepatocyte size, and was associated with increased hepatic inflammation. Furthermore, nuclear levels of the oncoprotein Yes Associated Protein (YAP) were increased and its transcriptional targets were induced in ChREBP-normalized GSD Ia mice. Hepatic ChREBP normalization furthermore induced DNA damage and mitotic activity in GSD Ia mice, while gene signatures of chromosomal instability, the cytosolic DNA-sensing cGAS-STING pathway, senescence, and hepatocyte dedifferentiation emerged.

CONCLUSIONS

In conclusion, our findings indicate that ChREBP activity limits hepatomegaly while decelerating liver disease progression and protecting against chromosomal instability in hepatic GSD Ia. These results disqualify ChREBP as a therapeutic target for treatment of liver disease in GSD Ia. In addition, they underline the importance of establishing the context-specific roles of hepatic ChREBP to define its therapeutic potential to prevent or treat advanced liver disease.

Gene therapy and genome editing for type I glycogen storage diseases

Type I glycogen storage diseases (GSD-I) consist of two major autosomal recessive disorders, GSD-Ia, caused by a reduction of glucose-6-phosphatase-α (G6Pase-α or G6PC) activity and GSD-Ib, caused by a reduction in the glucose-6-phosphate transporter (G6PT or SLC37A4) activity. The G6Pase-α and G6PT are functionally co-dependent. Together, the G6Pase-α/G6PT complex catalyzes the translocation of G6P from the cytoplasm into the endoplasmic reticulum lumen and its subsequent hydrolysis to glucose that is released into the blood to maintain euglycemia. Consequently, all GSD-I patients share a metabolic phenotype that includes a loss of glucose homeostasis and long-term risks of hepatocellular adenoma/carcinoma and renal disease. A rigorous dietary therapy has enabled GSD-I patients to maintain a normalized metabolic phenotype, but adherence is challenging. Moreover, dietary therapies do not address the underlying pathological processes, and long-term complications still occur in metabolically compensated patients. Animal models of GSD-Ia and GSD-Ib have delineated the disease biology and pathophysiology, and guided development of effective gene therapy strategies for both disorders. Preclinical studies of GSD-I have established that recombinant adeno-associated virus vector-mediated gene therapy for GSD-Ia and GSD-Ib are safe, and efficacious. A phase III clinical trial of rAAV-mediated gene augmentation therapy for GSD-Ia (NCT05139316) is in progress as of 2023. A phase I clinical trial of mRNA augmentation for GSD-Ia was initiated in 2022 (NCT05095727). Alternative genetic technologies for GSD-I therapies, such as gene editing, are also being examined for their potential to improve further long-term outcomes.

Amnio acid substitution at position 298 of human glucose-6 phosphatase-α significantly impacts its stability in mammalian cells

Glucose-6-phosphatase-α (G6Pase-α) catalyzes the hydrolysis of glucose-6-phosphate to glucose and functions as a key regulator in maintaining blood glucose homeostasis. Deficiency in G6Pase-α causes glycogen storage disease 1a (GSD1a), an inherited disorder characterized by life-threatening hypoglycemia and other long-term complications. We have developed a potential mRNA-based therapy for GSD1a and demonstrated that a human G6Pase-α (hG6Pase-α) variant harboring a single serine (S) to cysteine (C) substitution at the amino acid site 298 (S298C) had > twofold increase in protein expression, resulting in improved in vivo efficacy. Here, we sought to investigate the mechanisms contributing to the increased expression of the S298C variant. Mutagenesis of hG6Pase-α identified distinct protein variants at the 298 amino acid position with substantial reduction in protein expression in cultured cells. Kinetic analysis of expression and subcellular localization in mammalian cells, combined with cell-free in vitro translation assays, revealed that altered protein expression stemmed from differences in cellular protein stability rather than biosynthetic rates. Site-specific mutagenesis studies targeting other cysteines of the hG6Pase-α S298C variant suggest the observed improvements in stability are not due to additional disulfide bond formation. The glycosylation at Asparagine (N)-96 is critical in maintaining enzymatic activity and mutations at position 298 mainly affected glycosylated forms of hG6Pase-α. Finally, proteasome inhibition by lactacystin improved expression levels of unstable hG6Pase-α variants. Taken together, these data uncover a critical role for a single amino acid substitution impacting the stability of G6Pase-α and provide insights into the molecular genetics of GSD1a and protein engineering for therapeutic development.

Molecular mechanism underlying impaired hepatic autophagy in glycogen storage disease type Ib

Type Ib glycogen storage disease (GSD-Ib) is caused by a deficiency in the glucose-6-phosphate (G6P) transporter (G6PT) that translocates G6P from the cytoplasm into the endoplasmic reticulum lumen, where the intraluminal G6P is hydrolyzed to glucose by glucose-6-phosphatase-α (G6Pase-α). Clinically, GSD-Ib patients manifest a metabolic phenotype of impaired blood glucose homeostasis and a long-term risk of hepatocellular adenoma/carcinoma (HCA/HCC). Studies have shown that autophagy deficiency contributes to hepatocarcinogenesis. In this study, we show that G6PT deficiency leads to impaired hepatic autophagy evident from attenuated expression of many components of the autophagy network, decreased autophagosome formation and reduced autophagy flux. The G6PT-deficient liver displayed impaired sirtuin 1 (SIRT1) and AMP-activated protein kinase (AMPK) signaling, along with reduced expression of SIRT1, forkhead boxO3a (FoxO3a), liver kinase B-1 (LKB1) and the active p-AMPK. Importantly, we show that overexpression of either SIRT1 or LKB1 in G6PT-deficient liver restored autophagy and SIRT1/FoxO3a and LKB1/AMPK signaling. The hepatosteatosis in G6PT-deficient liver decreased SIRT1 expression. LKB1 overexpression reduced hepatic triglyceride levels, providing a potential link between LKB1/AMPK signaling upregulation and the increase in SIRT1 expression. In conclusion, downregulation of SIRT1/FoxO3a and LKB1/AMPK signaling underlies impaired hepatic autophagy which may contribute to HCA/HCC development in GSD-Ib. Understanding this mechanism may guide future therapies.

Impact of hematopoietic stem cell transplantation in glycogen storage disease type Ib: A single-subject research design using 13C-glucose breath test

Background

Glycogen storage disease type Ib (GSD Ib) is an autosomal recessively inherited deficiency of the glucose-6-phosphate translocase (G6PT). Clinical features include a combination of a metabolic phenotype (fasting hypoglycemia, lactic acidosis, hepatomegaly) and a hematologic phenotype with neutropenia and neutrophil dysfunction. Dietary treatment involves provision of starches such as uncooked cornstarch (UCCS) and Glycosade® to provide prolonged enteral supply of glucose. Granulocyte colony-stimulating factor (G-CSF) is the treatment of choice for neutropenia. Because long-term stimulation of hematopoiesis with G-CSF causes serious complications such as splenomegaly, hypersplenism, and osteopenia; hematopoietic stem cell transplantation (HSCT) has been considered in some patients with GSD Ib to correct neutropenia and avoid G-CSF related adverse effects. Whether HSCT also has an effect on the metabolic phenotype and utilization of carbohydrate sources has not been determined.

Objective

Our objective was to measure the utilization of starch in a patient with GSD Ib before and after HSCT using the minimally invasive ¹³C-glucose breath test (¹³C-GBT).

Design

A case of GSD Ib (18y; female) underwent ¹³C-GBT four times: UCCS (pre-HSCT), UCCS (3, 5 months post-HSCT) and Glycosade® (6 months post-HSCT) with a dose of 80 g administered via nasogastric tube after a 4 h fast according to our patient's fasting tolerance. Breath samples were collected at baseline and every 30 min for 240 min. Rate of CO₂ production was measured at 120 min using indirect calorimetry. Finger-prick blood glucose was measured using a glucometer hourly to test hypoglycemia (glucose <4 mmol/L). Biochemical and clinical data were obtained from the medical records as a post-hoc chart review.

Results

UCCS utilization was significantly higher in GSD Ib pre-HSCT, which reduced and stabilized 5 months post-HSCT. UCCS and Glycosade® utilizations were low and not different at 5 and 6 months post-HSCT. Blood glucose concentrations were not significantly different at any time point.

Conclusions

Findings show that HSCT stabilized UCCS utilization, as reflected by lower and stable glucose oxidation. The results also illustrate the application of ¹³C-GBT to examine glucose metabolism in response to various carbohydrate sources after other treatment modalities like HSCT in GSD Ib.

Current understanding on pathogenesis and effective treatment of glycogen storage disease type Ib with empagliflozin: new insights coming from diabetes for its potential implications in other metabolic disorders

Glycogen storage type Ib (GSDIb) is a rare inborn error of metabolism caused by glucose-6-phosphate transporter (G6PT, SLC37A4) deficiency. G6PT defect results in excessive accumulation of glycogen and fat in the liver, kidney, and intestinal mucosa and into both glycogenolysis and gluconeogenesis impairment. Clinical features include hepatomegaly, hypoglycemia, lactic acidemia, hyperuricemia, hyperlipidemia, and growth retardation. Long-term complications are liver adenoma, hepatocarcinoma, nephropathy and osteoporosis. The hallmark of GSDIb is neutropenia, with impaired neutrophil function, recurrent infections and inflammatory bowel disease. Alongside classical nutritional therapy with carbohydrates supplementation and immunological therapy with granulocyte colony-stimulating factor, the emerging role of 1,5-anhydroglucitol in the pathogenesis of neutrophil dysfunction led to repurpose empagliflozin, an inhibitor of the renal glucose transporter SGLT2: the current literature of its off-label use in GSDIb patients reports beneficial effects on neutrophil dysfunction and its clinical consequences. Surprisingly, this glucose-lowering drug ameliorated the glycemic and metabolic control in GSDIb patients. Furthermore, numerous studies from big cohorts of type 2 diabetes patients showed the efficacy of empagliflozin in reducing the cardiovascular risk, the progression of kidney disease, the NAFLD and the metabolic syndrome. Beneficial effects have also been described on peripheral neuropathy in a prediabetic rat model. Increasing evidences highlight the role of empagliflozin in regulating the cellular energy sensors SIRT1/AMPK and Akt/mTOR, which leads to improvement of mitochondrial structure and function, stimulation of autophagy, decrease of oxidative stress and suppression of inflammation. Modulation of these pathways shift the oxidative metabolism from carbohydrates to lipids oxidation and results crucial in reducing insulin levels, insulin resistance, glucotoxicity and lipotoxicity. For its pleiotropic effects, empagliflozin appears to be a good candidate for drug repurposing also in other metabolic diseases presenting with hypoglycemia, organ damage, mitochondrial dysfunction and defective autophagy.

Repurposing of Empagliflozin as a Possible Treatment for Neutropenia and Inflammatory Bowel Disease in Glycogen Storage Disease Type Ib: A Case Report

Glycogen storage disease type Ib (GSD-Ib) is an autosomal-recessive inborn error of carbohydrate metabolism, where severe fasting hypoglycemia is associated (among other manifestations) with neutropenia and neutrophil dysfunction (predisposing to recurrent, potentially life-threatening infections) and inflammatory bowel disease (IBD). Granulocyte colony-stimulating factors (G-CSFs) are commonly used for its treatment. Although they have improved the prognosis of the disease, these medicines have also led to concerns about complications associated with their use (namely splenomegaly and hematopoietic malignancies), not to mention their increased cost. Recently, a novel new treatment for neutropenia associated with this disease was discovered. It was found that sodium-glucose cotransporter type 2 (SGLT-2) inhibitors, usually used for the treatment of diabetes mellitus, can ameliorate both neutropenia and IBD-related symptoms and improve the quality of life in patients suffering from these diseases. They do it by inhibiting the renal reabsorption of 1,5-anhydroglucitol, a dietary analog of glucose, whose accumulation due to the specific enzyme deficiency leads to toxic effects on granulocytes. Herein we report the treatment of an adult patient suffering from GSD-Ib with empagliflozin, an SGLT-2 inhibitor.

Untargeted metabolomic profiling in a patient with glycogen storage disease Ib receiving empagliflozin treatment

Glycogen storage disease type Ib (GSD-Ib) is a rare inborn error of glycogen metabolism uniquely associated with neutropenia and neutrophil dysfunction, causing severe infections, inflammatory bowel disease (IBD), and impaired wound healing. Recently, kidney sodium-glucose co-transporter-2 (SGLT2) inhibitors such as empagliflozin known to reduce plasma levels of 1,5-anhydroglucitol (1,5-AG) and its toxic derivatives in neutrophils, have been described as a new treatment option in case reports of patients with GSD-Ib from Europe and Asia. We report our experience with an 11-year-old girl with GSD-Ib presenting with short fasting hypoglycemia, neutropenia with neutrophil dysfunction, recurrent infections, suboptimal growth, iron-deficiency anemia, and IBD. Treatment with daily empagliflozin improved neutrophil counts and function with a significant reduction in G-CSF needs. Significant improvement in IBD has led to weight gain with improved nutritional markers and improved fasting tolerance. Reduction of maximum empagliflozin dose was needed due to arthralgia. No other significant side effects of empagliflozin were observed. This report uniquely highlights the novel use of untargeted metabolomics profiling for monitoring plasma levels of 1,5-AG to assess empagliflozin dose responsiveness and guide dietary management and G-CSF therapy. Clinical improvement correlated to rapid normalization of 1,5-AG levels in plasma sustained after dose reduction. In conclusion, empagliflozin appeared to be a safe treatment option for GSD-Ib-associated neutropenia and neutrophil dysfunction. Global untargeted metabolomics is an efficient method to assess biochemical responsiveness to treatment.

Increased atherosclerosis in a mouse model of glycogen storage disease type 1a

Glycogen storage disease type 1a (GSD Ia) is an inborn error of carbohydrate metabolism. Despite severe hyperlipidemia, GSD Ia patients show limited atherogenesis compared to age-and-gender matched controls. Employing a GSD Ia mouse model that resembles the severe hyperlipidemia in patients, we here found increased atherogenesis in GSD Ia. These data provide a rationale for investigating atherogenesis in GSD Ia in a larger patient cohort.

Biophysical and functional properties of purified glucose-6-phosphatase catalytic subunit 1

Glucose-6-phosphatase catalytic subunit 1 (G6PC1) plays a critical role in hepatic glucose production during fasting by mediating the terminal step of the gluconeogenesis and glycogenolysis pathways. In concert with accessory transport proteins, this membrane-integrated enzyme catalyzes glucose production from glucose-6-phosphate (G6P) to support blood glucose homeostasis. Consistent with its metabolic function, dysregulation of G6PC1 gene expression contributes to diabetes, and mutations that impair phosphohydrolase activity form the clinical basis of glycogen storage disease type 1a. Despite its relevance to health and disease, a comprehensive view of G6PC1 structure and mechanism has been limited by the absence of expression and purification strategies that isolate the enzyme in a functional form. In this report, we apply a suite of biophysical and biochemical tools to fingerprint the in vitro attributes of catalytically active G6PC1 solubilized in lauryl maltose neopentyl glycol (LMNG) detergent micelles. When purified from Sf9 insect cell membranes, the glycosylated mouse ortholog (mG6PC1) recapitulated functional properties observed previously in intact hepatic microsomes and displayed the highest specific activity reported to date. Additionally, our results establish a direct correlation between the catalytic and structural stability of mG6PC1, which is underscored by the enhanced thermostability conferred by phosphatidylcholine and the cholesterol analog cholesteryl hemisuccinate. In contrast, the N96A variant, which blocks N-linked glycosylation, reduced thermostability. The methodologies described here overcome long-standing obstacles in the field and lay the necessary groundwork for a detailed analysis of the mechanistic structural biology of G6PC1 and its role in complex metabolic disorders.

Evaluation of Glycogen Storage Patients: Report of Twelve Novel Variants and New Clinical Findings in a Turkish Population

Glycogen storage diseases (GSDs) are clinically and genetically heterogeneous disorders that disturb glycogen synthesis or utilization. Although it is one of the oldest inherited metabolic disorders, new genetic methods and long-time patient follow-ups provide us with unique insight into the genotype-phenotype correlations. The aim of this study was to share the phenotypic features and molecular diagnostic results that include new pathogenic variants in our GSD cases. Twenty-six GSD patients were evaluated retrospectively. Demographic data, initial laboratory and imaging features, and current findings of the patients were recorded. Molecular analysis results were classified as novel or previously defined variants. Novel variants were analyzed with pathogenicity prediction tools according to American College of Medical Genetics and Genomics (ACGM) criteria. Twelve novel and rare variants in six different genes were associated with the disease. Hearing impairment in two patients with GSD I, early peripheral neuropathy after liver transplantation in one patient with GSD IV, epilepsy and neuromotor retardation in three patients with GSD IXA were determined. We characterized a heterogeneous group of all diagnosed GSDs over a 5-year period in our institution, and identified novel variants and new clinical findings. It is still difficult to establish a genotype-phenotype correlation in GSDs.

Modeling Phenotypic Heterogeneity of Glycogen Storage Disease Type 1a Liver Disease in Mice by Somatic CRISPR/CRISPR-associated protein 9-Mediated Gene Editing

BACKGROUND AND AIMS

Patients with glycogen storage disease type 1a (GSD-1a) primarily present with life-threatening hypoglycemia and display severe liver disease characterized by hepatomegaly. Despite strict dietary management, long-term complications still occur, such as liver tumor development. Variations in residual glucose-6-phosphatase (G6PC1) activity likely contribute to phenotypic heterogeneity in biochemical symptoms and complications between patients. However, lack of insight into the relationship between G6PC1 activity and symptoms/complications and poor understanding of the underlying disease mechanisms pose major challenges to provide optimal health care and quality of life for GSD-1a patients. Currently available GSD-1a animal models are not suitable to systematically investigate the relationship between hepatic G6PC activity and phenotypic heterogeneity or the contribution of gene-gene interactions (GGIs) in the liver.

APPROACH AND RESULTS

To meet these needs, we generated and characterized a hepatocyte-specific GSD-1a mouse model using somatic CRISPR/CRISPR-associated protein 9 (Cas9)-mediated gene editing. Hepatic G6pc editing reduced hepatic G6PC activity up to 98% and resulted in failure to thrive, fasting hypoglycemia, hypertriglyceridemia, hepatomegaly, hepatic steatosis (HS), and increased liver tumor incidence. This approach was furthermore successful in simultaneously modulating hepatic G6PC and carbohydrate response element-binding protein, a transcription factor that is activated in GSD-1a and protects against HS under these conditions. Importantly, it also allowed for the modeling of a spectrum of GSD-1a phenotypes in terms of hepatic G6PC activity, fasting hypoglycemia, hypertriglyceridemia, hepatomegaly and HS.

CONCLUSIONS

In conclusion, we show that somatic CRISPR/Cas9-mediated gene editing allows for the modeling of a spectrum of hepatocyte-borne GSD-1a disease symptoms in mice and to efficiently study GGIs in the liver. This approach opens perspectives for translational research and will likely contribute to personalized treatments for GSD-1a and other genetic liver diseases.

Hepatocyte-specific glucose-6-phosphatase deficiency disturbs platelet aggregation and decreases blood monocytes upon fasting-induced hypoglycemia

OBJECTIVE

Glycogen storage disease type 1a (GSD Ia) is a rare inherited metabolic disorder caused by mutations in the glucose-6-phosphatase (G6PC1) gene. When untreated, GSD Ia leads to severe fasting-induced hypoglycemia. Although current intensive dietary management aims to prevent hypoglycemia, patients still experience hypoglycemic events. Poor glycemic control in GSD Ia is associated with hypertriglyceridemia, hepatocellular adenoma and carcinoma, and also with an increased bleeding tendency of unknown origin.

METHODS

To evaluate the effect of glycemic control on leukocyte levels and coagulation in GSD Ia, we employed hepatocyte-specific G6pc1 deficient (L-G6pc-/-) mice under fed or fasted conditions, to match good or poor glycemic control in GSD Ia, respectively.

RESULTS

We found that fasting-induced hypoglycemia in L-G6pc-/- mice decreased blood leukocytes, specifically proinflammatory Ly6Chi monocytes, compared to controls. Refeeding reversed this decrease. The decrease in Ly6Chi monocytes was accompanied by an increase in plasma corticosterone levels and was prevented by the glucocorticoid receptor antagonist mifepristone. Further, fasting-induced hypoglycemia in L-G6pc-/- mice prolonged bleeding time in the tail vein bleeding assay, with reversal by refeeding. This could not be explained by changes in coagulation factors V, VII, or VIII, or von Willebrand factor. While the prothrombin and activated partial thromboplastin time as well as total platelet counts were not affected by fasting-induced hypoglycemia in L-G6pc-/- mice, ADP-induced platelet aggregation was disturbed.

CONCLUSIONS

These studies reveal a relationship between fasting-induced hypoglycemia, decreased blood monocytes, and disturbed platelet aggregation in L-G6pc-/- mice. While disturbed platelet aggregation likely accounts for the bleeding phenotype in GSD Ia, elevated plasma corticosterone decreases the levels of proinflammatory monocytes. These studies highlight the necessity of maintaining good glycemic control in GSD Ia.

The SGLT2-inhibitor dapagliflozin improves neutropenia and neutrophil dysfunction in a mouse model of the inherited metabolic disorder GSDIb

Glycogen Storage Disease type 1b (GSDIb) is a genetic disorder with long term severe complications. Accumulation of the glucose analog 1,5-anhydroglucitol-6-phosphate (1,5AG6P) in neutrophils inhibits the phosphorylation of glucose in these cells, causing neutropenia and neutrophil dysfunctions. This condition leads to serious infections and inflammatory bowel disease (IBD) in GSDIb patients. We show here that dapagliflozin, an inhibitor of the renal sodium-glucose co-transporter-2 (SGLT2), improves neutrophil function in an inducible mouse model of GSDIb by reducing 1,5AG6P accumulation in myeloid cells.

Glycogen Storage Disease Type Ia: Current Management Options, Burden and Unmet Needs

Glycogen storage disease type Ia (GSDIa) is caused by defective glucose-6-phosphatase, a key enzyme in carbohydrate metabolism. Affected individuals cannot release glucose during fasting and accumulate excess glycogen and fat in the liver and kidney, putting them at risk of severe hypoglycaemia and secondary metabolic perturbations. Good glycaemic/metabolic control through strict dietary treatment and regular doses of uncooked cornstarch (UCCS) is essential for preventing hypoglycaemia and long-term complications. Dietary treatment has improved the prognosis for patients with GSDIa; however, the disease itself, its management and monitoring have significant physical, psychological and psychosocial burden on individuals and parents/caregivers. Hypoglycaemia risk persists if a single dose of UCCS is delayed/missed or in cases of gastrointestinal intolerance. UCCS therapy is imprecise, does not treat the cause of disease, may trigger secondary metabolic manifestations and may not prevent long-term complications. We review the importance of and challenges associated with achieving good glycaemic/metabolic control in individuals with GSDIa and how this should be balanced with age-specific psychosocial development towards independence, management of anxiety and preservation of quality of life (QoL). The unmet need for treatment strategies that address the cause of disease, restore glucose homeostasis, reduce the risk of hypoglycaemia/secondary metabolic perturbations and improve QoL is also discussed.

The signaling pathways implicated in impairment of hepatic autophagy in glycogen storage disease type Ia

Glucose-6-phosphatase-α (G6Pase-α or G6PC) deficiency in glycogen storage disease type-Ia (GSD-Ia) leads to impaired hepatic autophagy, a recycling process important for cellular metabolism and homeostasis. Autophagy can be regulated by several energy sensing pathways, including sirtuin 1 (SIRT1), forkhead box O (FoxO), AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor-α (PPAR-α), and mammalian target of rapamycin (mTOR). Using 10-day old global G6pc-deficient (G6pc-/-) mice, hepatic autophagy impairment was attributed to activation of mTOR and inhibition of AMPK signaling. In other studies, using adult liver-specific G6pc-deficient mice at both pre-tumor and tumor stages, hepatic autophagy impairment was attributed to downregulation of SIRT1 signaling and mTOR was not implicated. In this study, we provide a detailed analysis of the major autophagy pathways in young G6pc-/- mice over the first 4 weeks of life. We show that impaired SIRT1, FoxO3a, AMPK, and PPAR-α signaling are responsible for autophagy impairment but mTOR is involved minimally. Hepatic SIRT1 overexpression corrects defective autophagy, restores the expression of FoxO3a and liver kinase B1 but fails to normalize impaired PPAR-α expression or metabolic abnormalities associated with GSD-Ia. Importantly, restoration of hepatic G6Pase-α expression in G6pc-/- mice corrects defective autophagy, restores SIRT1/FoxO3a/AMPK/PPAR-α signaling and rectifies metabolic abnormalities. Taken together, these data show that hepatic autophagy impairment in GSD-Ia is mediated by downregulation of SIRT1/FoxO3a/AMPK/PPAR-α signaling.

Classifying molecular phenotypes of G6PC variants for pathogenic properties and to guide therapeutic development

Due to advances in sequencing technologies, identification of genetic variants is rapid. However, the functional consequences of most genomic variants remain unknown. Consequently, variants of uncertain significance (VUS) that appear in clinical DNA diagnostic reports lack sufficient data for interpretation. Algorithms exist to aid prediction of a variant's likelihood of pathogenicity, but these predictions usually lack empiric evidence. To examine the feasibility of generating functional evidence in vitro for a given variant's role in disease, a panel of 29 coding sequence variants in the G6PC gene was assessed. G6PC encodes glucose-6 phosphatase enzyme, and reduction in its function causes the rare metabolic disease glycogen storage disease type 1a (GSD1a). Variants were heterologously expressed as fusion proteins in a hepatocyte-derived cell line and examined for effects on steady-state protein levels, biosynthetic processing, and intracellular distribution. The screen revealed variant effects on protein levels, N-linked glycosylation status, and cellular distribution. Of the eight VUS tested, seven behaved similar to wild-type protein while one VUS, p.Cys109Tyr, exhibited features consistent with pathogenicity for all molecular phenotypes assayed, including significantly reduced protein levels, alteration in protein glycosylation status, and abnormally diffuse protein localization pattern, and has recently been reported in a patient with GSD1a. Our results show that such a screen can add empiric evidence to existing databases to aid in diagnostics, and also provides further classification for molecular phenotypes that could be used in future therapeutic screening approaches for small molecule or gene editing strategies directed at specific variants.

A case study of glycogen storage disease type Ia presenting with multiple hepatocellular adenomas: an analysis by gadolinium ethoxybenzyl-diethylenetriamine-pentaacetic acid magnetic resonance imaging

Glycogen storage disease type Ia (GSD Ia) is a rare disease caused by a deficiency of hepatic glucose-6-phosphatase (G6Pase). Here, we report a 17-year-old Chinese boy with GSD Ia. Clinical manifestations of the patient included hepatomegaly, growth retardation, doll face, and biochemical abnormalities, including hypoglycaemia, hyperuricaemia, and hyperlipidaemia. The computed tomography (CT) and gadolinium ethoxybenzyl-diethylenetriamine-pentaacetic acid (Gd-EOB-DTPA) magnetic resonance imaging (MRI) revealed multiple masses in the left and right hemiliver. These masses presented as different dynamic enhanced patterns in the Gd-EOB-DTPA MRI. In addition, a large amount of glycogen deposit was detected in the liver tissue biopsy. Liver puncture confirmed that the masses were hepatocellular adenomas (HCAs). Genetic analyses confirmed the presence of liver metabolic disease, and the final clinical diagnostic was GSD Ia. The patient's clinical manifestations were significantly improved following regular treatment with raw corn starch for 9 months. Unfortunately, it was suspected that parts of the adenoma had undergone malignant transformation.

mRNA therapy restores euglycemia and prevents liver tumors in murine model of glycogen storage disease

Glycogen Storage Disease 1a (GSD1a) is a rare, inherited metabolic disorder caused by deficiency of glucose 6-phosphatase (G6Pase-α). G6Pase-α is critical for maintaining interprandial euglycemia. GSD1a patients exhibit life-threatening hypoglycemia and long-term liver complications including hepatocellular adenomas (HCAs) and carcinomas (HCCs). There is no treatment for GSD1a and the current standard-of-care for managing hypoglycemia (Glycosade®/modified cornstarch) fails to prevent HCA/HCC risk. Therapeutic modalities such as enzyme replacement therapy and gene therapy are not ideal options for patients due to challenges in drug-delivery, efficacy, and safety. To develop a new treatment for GSD1a capable of addressing both the life-threatening hypoglycemia and HCA/HCC risk, we encapsulated engineered mRNAs encoding human G6Pase-α in lipid nanoparticles. We demonstrate the efficacy and safety of our approach in a preclinical murine model that phenotypically resembles the human condition, thus presenting a potential therapy that could have a significant therapeutic impact on the treatment of GSD1a.

LONG TERM MANAGEMENT OF GLYCOGEN STORAGE DISEASE TYPE 1B: A BRAZILIAN TERTIARY CENTER EXPERIENCE

BACKGROUND

Glycogen storage disease (GSD) type 1b is a multisystemic disease in which immune and infectious complications are present, in addition to the well-known metabolic manifestations of GSD. Treatment with granulocyte-colony stimulating factor (G-CSF) is often indicated in the management of neutropenia and inflammatory bowel disease.

OBJECTIVE

To report on the demographics, genotype, clinical presentation, management, and complications of pediatric patients with glycogen storage disease type 1b (GSD 1b), with special attention to immune-related complications.

METHODS

Retrospective case series of seven patients with GSD 1b diagnosed and followed at a tertiary university hospital in Brazil, from July/2000 until July/2016.

RESULTS

Mean age at referral was fourteen months. Diagnosis of GSD 1b was based on clinical and laboratory findings and supported by genetic studies in five cases. All patients presented suffered from neutropenia, managed with G-CSF - specifically Filgrastim. Hospitalizations for infections were frequent. Two patients developed inflammatory bowel disease. Six patients remained alive, one died at age 14 years and 9 months. The mean age at the end of the follow-up was 11.5 years. Compliance to treatment was suboptimal: poor compliance to medications, starch and dietetic management of GSD were documented, and outpatient appointments were frequently missed.

CONCLUSION

Managing GSD 1b is challenging not only for the chronic and multisystemic nature of this disease, but also for the additional demands related dietary restrictions, use of multiple medications and the need for frequent follow-up visits; furthermore in Brazil, the difficulties are increased in a scenario where we frequently care for patients with unfavorable socioeconomic status and with irregular supply of medications in the public health system.

Correction of metabolic abnormalities in a mouse model of glycogen storage disease type Ia by CRISPR/Cas9-based gene editing

Glycogen storage disease type Ia (GSD-Ia), deficient in glucose-6-phosphatase-α (G6PC), is characterized by impaired glucose homeostasis and a hallmark of fasting hypoglycemia. We have developed a recombinant adeno-associated virus (rAAV) vector-mediated gene therapy for GSD-Ia that is currently in a phase I/II clinical trial. While therapeutic expression of the episomal rAAV-G6PC clinical vector is stable in mice, the long-term durability of expression in humans is currently being established. Here we evaluated CRISPR/Cas9-based in vivo genome editing technology to correct a prevalent pathogenic human variant, G6PC-p.R83C. We have generated a homozygous G6pc-R83C mouse strain and shown that the G6pc-R83C mice manifest impaired glucose homeostasis and frequent hypoglycemic seizures, mimicking the pathophysiology of GSD-Ia patients. We then used a CRISPR/Cas9-based gene editing system to treat newborn G6pc-R83C mice and showed that the treated mice grew normally to age 16 weeks without hypoglycemia seizures. The treated G6pc-R83C mice, expressing ≥ 3% of normal hepatic G6Pase-α activity, maintained glucose homeostasis, displayed normalized blood metabolites, and could sustain 24 h of fasting. Taken together, we have developed a second-generation therapy in which in vivo correction of a pathogenic G6PC-p.R83C variant in its native genetic locus could lead to potentially permanent, durable, long-term correction of the GSD-Ia phenotype.

Inborn errors of immunity and metabolic disorders: current understanding, diagnosis, and treatment approaches

Inborn errors of metabolism consist of a heterogeneous group of disorders with various organ systems manifestations, and some metabolic diseases also cause immunological disorders or dysregulation. In this review, metabolic diseases that affect the immunological system and particularly lead to primary immune deficiency will be reviewed. In a patient with frequent infections and immunodeficiency, the presence of symptoms such as growth retardation, abnormal facial appearance, heart, skeletal, lung deformities, skin findings, arthritis, motor developmental retardation, seizure, deafness, hepatomegaly, splenomegaly, impairment of liver function tests, the presence of anemia, thrombocytopenia and eosinophilia in hematological examinations should suggest metabolic diseases for the underlying cause. In some patients, these phenotypic findings may appear before the immunodeficiency picture. Metabolic diseases leading to immunological disorders are likely to be rare but probably underdiagnosed. Therefore, the presence of recurrent infections or autoimmune findings in a patient with a suspected metabolic disease should suggest that immune deficiency may also accompany the picture, and diagnostic examinations in this regard should be deepened.

Clinical analysis and long-term treatment monitoring of 3 patients with glycogen storage disease type Ib

BACKGROUND

To investigate the clinical and genetic characteristics of patients with glycogen storage disease type Ib (GSD Ib).

CASE PRESENTATION

This report retrospectively analyzed the clinical data of 3 patients with GSD Ib admitted into our hospital, and summarized their onset characteristics, clinical manifestations, related examinations and treatment as well as mutational spectrum. After gene sequencing, the diagnosis of GSD Ib was confirmed in all 3 patients. Five variants of SLC37A4 gene were detected, of which c. 572C > T was the common variant and c. 680G > A was a novel variant. The 3 cases of GSD Ib were mainly affected by liver enlargement, growth retardation, etc., and all had a history of repeated infections. At the onset, patients mainly manifested as mildly elevated alanine-aminotransferase (ALT), accompanied by decreased absolute neutrophil count (ANC), hypertriglyceridemia, and metabolic disorders (hypoglycemia, hyperlactic acidemia, metabolic acidosis, etc.). After long-term treatment by oral uncooked cornstarch, the abnormal liver enzymes gradually returned to normal, and metabolic abnormalities were basically controlled most of the time. With increasing age, ANC of 2 patients decreased progressively, whereas the times of infections was reduced.

CONCLUSIONS

We reported 3 cases with GSD Ib and a novel SLC37A4 variant. The possibility of GSD type Ib should be kept on alert when a patient suffers recurrent infections, accompanied by hepatomegaly, elevated liver enzymes, hypoglycemia, dyslipidemia, and metabolic disorders.

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.