Characterization of glycogen molecular structure in the worm Caenorhabditis elegans.

Glycogen, a glucose homopolymer with many glucose chains, is the primary blood-sugar reservoir in many organisms. It comprises ß particles (∼20 nm) which can bind together to form large α particles with a rosette morphology. When dimethyl sulfoxide (DMSO) is added to glycogen from diabetic livers, α particles break apart to ß particles ('fragility'), possibly due to H-bond disruption; this is not seen in healthy livers. Glycogen α and ß particles, and α-particle fragility, are observed in mammals and bacteria, and are examined here in the worm Caenorhabditis elegans, with glycogen from two C. elegans strains, cultured in normal and high-glucose conditions. There were mainly ß particles, with some large α particles. Most particles were fragile in DMSO. Growing in a high-glucose medium results in more long chains and more fragility, consistent with previous observations in diabetic animal models. Why high glucose levels facilitate fragility is worthy of further investigation.

Glycogen Dynamics Drives Lipid Droplet Biogenesis during Brown Adipocyte Differentiation.

Browning induction or transplantation of brown adipose tissue (BAT) or brown/beige adipocytes derived from progenitor or induced pluripotent stem cells (iPSCs) can represent a powerful strategy to treat metabolic diseases. However, our poor understanding of the mechanisms that govern the differentiation and activation of brown adipocytes limits the development of such therapy. Various genetic factors controlling the differentiation of brown adipocytes have been identified, although most studies have been performed using in vitro cultured pre-adipocytes. We investigate here the differentiation of brown adipocytes from adipose progenitors in the mouse embryo. We demonstrate that the formation of multiple lipid droplets (LDs) is initiated within clusters of glycogen, which is degraded through glycophagy to provide the metabolic substrates essential for de novo lipogenesis and LD formation. Therefore, this study uncovers the role of glycogen in the generation of LDs.

Molecular Structure of Glycogen in Escherichia coli.

Glycogen, a randomly branched glucose polymer, provides energy storage in organisms. It forms small ß particles which in animals bind to form composite α particles, which give better glucose release. Simulations imply ß particle size is controlled only by activities and sizes of glycogen biosynthetic enzymes and sizes of polymer chains. Thus, storing more glucose requires forming more ß particles, which are expected to sometimes form α particles. No α particles have been reported in bacteria, but the extraction techniques might have caused degradation. Using milder glycogen extraction techniques on Escherichia coli, transmission electron microscopy and size-exclusion chromatography showed α particles, consistent with this hypothesis for α-particle formation. Molecular density and size distributions show similarities with animal glycogen, despite very different metabolic processes. These general polymer constraints are such that any organism which needs to store and then release glucose will have similar α and ß particle structures: a type of convergent evolution.

Long-Term Hypoxic Tolerance in Murine Cornea.

Kosaku, Kazuhiro, Tomonori Harada, Toyoharu Jike, Isao Tsuboi, and Shin Aizawa. Long-term hypoxic tolerance in murine cornea. High Alt Med Biol 19:35-41, 2018. AIMS: The cornea is believed to be an exceedingly sensitive organ to decreases in atmospheric oxygen concentrations. Previous corneal studies have shown the hypoxic tolerance of the cornea during short-term and local hypoxic exposure. This study investigated the tolerance of the cornea during long-term and systemic hypoxia. METHODS AND RESULTS: Mice were bred under normobaric normoxia or hypoxia (10% oxygen concentration) conditions for 140 days. The layer structure, surface microvilli, and glycogen granules in the corneal epithelium were examined on day 2 and on day 140. The layer and surface structures of the corneal epithelium were normally maintained during the long-term hypoxia. Hypoxic stress caused a decrease in the glycogen granules in the corneal epithelial cells. CONCLUSIONS: Maintenance of normal structures during long-term hypoxia suggests that the cornea has a high tolerance for hypoxic stress. The quantity of glycogen in corneal epithelial cells is considered an index of corneal hypoxia resistance.

Glycogen Synthesis in Glycogenin 1-Deficient Patients: A Role for Glycogenin 2 in Muscle.

Context: Glycogen storage disease (GSD) type XV is a rare disease caused by mutations in the GYG1 gene that codes for the core molecule of muscle glycogen, glycogenin 1. Nonetheless, glycogen is present in muscles of glycogenin 1-deficient patients, suggesting an alternative for glycogen buildup. A likely candidate is glycogenin 2, an isoform expressed in the liver and heart but not in healthy skeletal muscle. Objective: We wanted to investigate the formation of glycogen and changes in glycogen metabolism in patients with GSD type XV. Design, Setting, and Patients: Two patients with mutations in the GYG1 gene were investigated for histopathology, ultrastructure, and expression of proteins involved in glycogen synthesis and metabolism. Results: Apart from occurrence of polyglucosan (PG) bodies in few fibers, glycogen appeared normal in most cells, and the concentration was normal in patients with GSD type XV. We found that glycogenin 1 was absent, but glycogenin 2 was present in the patients, whereas the opposite was the case in healthy controls. Electron microscopy revealed that glycogen was present between and not inside myofibrils in type II fibers, compromising the ultrastructure of these fibers, and only type I fibers contained PG bodies. We also found significant changes to the expression levels of several enzymes directly involved in glycogen and glucose metabolism. Conclusions: To our knowledge, this is the first report demonstrating expression of glycogenin 2 in glycogenin 1-deficient patients, suggesting that glycogenin 2 rescues the formation of glycogen in patients with glycogenin 1 deficiency.

Characterization of the highly branched glycogen from the thermoacidophilic red microalga Galdieria sulphuraria and comparison with other glycogens.

The thermoacidophilic red microalga Galdieria sulphuraria synthesizes glycogen when growing under heterotrophic conditions. Structural characterization revealed that G. sulphuraria glycogen is the most highly branched glycogen described to date, with 18% of α-(1→6) linkages. Moreover, it differs from other glycogens because it is composed of short chains only and has a substantially smaller molecular weight and particle size. The physiological role of this highly branched glycogen in G. sulphuraria is discussed.

Acid hydrolysis and molecular density of phytoglycogen and liver glycogen helps understand the bonding in glycogen α (composite) particles.

Phytoglycogen (from certain mutant plants) and animal glycogen are highly branched glucose polymers with similarities in structural features and molecular size range. Both appear to form composite α particles from smaller ß particles. The molecular size distribution of liver glycogen is bimodal, with distinct α and ß components, while that of phytoglycogen is monomodal. This study aims to enhance our understanding of the nature of the link between liver-glycogen ß particles resulting in the formation of large α particles. It examines the time evolution of the size distribution of these molecules during acid hydrolysis, and the size dependence of the molecular density of both glucans. The monomodal distribution of phytoglycogen decreases uniformly in time with hydrolysis, while with glycogen, the large particles degrade significantly more quickly. The size dependence of the molecular density shows qualitatively different shapes for these two types of molecules. The data, combined with a quantitative model for the evolution of the distribution during degradation, suggest that the bonding between ß into α particles is different between phytoglycogen and liver glycogen, with the formation of a glycosidic linkage for phytoglycogen and a covalent or strong non-covalent linkage, most probably involving a protein, for glycogen as most likely. This finding is of importance for diabetes, where α-particle structure is impaired.

Labral gland in soldiers of the neotropical termite Cornitermes cumulans (Isoptera: Termitidae: Syntermitinae).

Cornitermes cumulans is a termite species of the subfamily Syntermitinae with a nasute mandibulate soldier caste, members of which are morphologically equipped with structures and organs specialized for the defence of the colony. We investigated the labrum of soldiers of C. cumulans and described the labral gland, an exocrine structure present in this appendage. The labrum of C. cumulans soldiers presented two distinct regions, the hyaline tip and the proximal region connected to the head. The hyaline tip exhibited a thick cuticle composed of a loose endocuticle involving an epithelium of class 1 cells, which synthesize the glandular product into a subcuticular space that function as a reservoir prior to release the final secretion. The proximal region of the labrum had an epithelium composed of class 1 and class 3 cells, which released the secretion onto both ventral and dorsal surfaces. The ultrastructure showed abundant smooth endoplasmic reticulum and glycogen in the class 1 cells, whereas the class 3 cells had many electron-lucent vesicles that varied in size. We associated the labral gland with the production of toxic substances that may act inside enemy wounds made by the soldiers' mandibles. Other possible functions for the labral secretion are also discussed.

Improving size-exclusion chromatography separation for glycogen.

Glycogen is a hyperbranched glucose polymer comprised of glycogen ß particles, which can also form much larger composite α particles. The recent discovery using size-exclusion chromatography (SEC) that fewer, smaller, α particles are found in diabetic-mouse liver compared to healthy mice highlights the need to achieve greater accuracy in the size separation methods used to analyze α and ß particles. While past studies have used dimethyl sulfoxide as the SEC eluent to analyze the molecular size and structure of native glycogen, an aqueous eluent has not been rigorously tested and compared with dimethyl sulfoxide. The conditions for SEC of pig-liver glycogen, phytoglycogen and oyster glycogen were optimized by comparing two different eluents, aqueous 50 mM NH4NO3/0.02% NaN3 and dimethyl sulfoxide/0.5% LiBr, run through different column materials and pore sizes at various flow rates. The aqueous system gave distinct size separation of α- and ß-particle peaks, allowing for a more detailed and quantitative analysis and comparison between liver glycogen samples. This greater resolution has also revealed key differences between the structure of liver glycogen and phytoglycogen.

Urethral striated muscle and extracellular matrix morphological characteristics among mildly diabetic pregnant rats: translational approach.

INTRODUCTION AND HYPOTHESIS: Diabetes mellitus (DM) during pregnancy is associated with high levels of urinary incontinence (UI) and pelvic floor muscle dysfunction. Mild DM can lead to changes in urethral striated muscle and extracellular matrix (ECM) in pregnant rats considering both structures as an entire system responsible for urinary continence. METHODS: Ninety-two female Wistar rats were distributed in four experimental groups: virgin, pregnant, diabetic, and diabetic pregnant. In adult life, parental nondiabetic female rats were mated with nondiabetic male rats to obtain newborns. At the first day of birth, newborns received citrate buffer (nondiabetic group) or streptozotocin 100 mg/kg body weight, subcutaneous route (mild DM group). At day 21 of the pregnancy, the rats were lethally anesthetized and the urethra and vagina were extracted as a unit. Urethral and vaginal sections were cut and analyzed by: (a) cytochemical staining for ECM and muscle structural components, (b) immunohistochemistry to identify fast- and slow-muscle fibers, and (c) transmission electron microscopy for ultrastructural analysis of urethral striated muscle. RESULTS: In comparison with the three control groups, variations in the urethral striated muscle and ECM from diabetic pregnant rats were observed including thinning, atrophy, fibrosis, increased area of blood vessels, mitochondria accumulation, increased lipid droplets, glycogen granules associated with colocalization of fast and slow fibers, and a steady decrease in the proportion of fast to slow fibers. CONCLUSIONS: Mild DM and pregnancy can lead to a time-dependent disorder and tissue remodeling in which the urethral striated muscle and ECM has a fundamental function.

[Dynamics of pro- and macroglycogen content in hepatocytes of normal and cirrhotic rat liver at different stages of glycogenesis].

The content and structure of glycogen in hepatocytes of normal and cirrhotic rat liver has been studied at definite time intervals after the administration of glucose to starving animals. In the study, an original cytofluorimetric method for detection and quatification of proglycogen (PG) and macroglycogen (MG) content in isolated hepatocytes was applied. This method is based on using Schiff reagents with different spectral characteristics. It has been determined that the content MG content in the hepatocytes of control rats increases in 10 min after initiation of glycogenesis by 52% (P < 0.01). MG content in the cells of cirrhotic liver increased only after 20 min (43%, P < 0.05) after glucose administration to starving animals. The coefficient of correlation between MG content and the total glycogen content in the hepatocytes at different stages of glycogenesis ranged from 0.90 to 0.99 (P < 0.001) in both groups of rats. Increase in PG content in hepatocytes of control rats appeared within 10-30 and 45-70 min. In the case of cirrhosis PG content increased only 60 min after the start of glycogenesis, but after 120 min it was 1.5 times higher than the control values (P < 0.001). The correlation coefficient between the PG and the total glycogen content in rat liver cells averaged 0.86 (P < 0.001) and 0.77 (P < 0.001) in control and experimental groups, respectively. Thus, the change in total glycogen content in hepatocytes of normal and cirrhotic liver is associated mainly with the level of MG. In normal cells, contribution of PG is most significant in the early glycogenesis (10-30 min), and in the cirrhotic liver--in the later stages.

Clinicopathological, genetic, ultrastructural characterizations and prognostic factors of papillary renal cell carcinoma: new diagnostic and prognostic information.

Papillary renal cell carcinoma (PRCC) includes two different morphological subtypes. The differences of genetics and ultrastructure of the two subtypes have been rarely reported. Also, new biomarkers related to the diagnosis and prognosis of PRCC have still not been well elucidated. Immunohistochemistry, fluorescence in situ hybridization (FISH) and transmission electron microscopy were used systematically to determine the characteristics of 56 cases of PRCC and to reveal new diagnostic and prognostic information. Type 1 PRCC presented higher expression rates of EMA and CK7, whereas type 2 presented a higher expression rate of CD10. New immunohistochemical markers, including: p504s, PAX-2, PAX-8 and CA-IX showed extensive immunostaining in PRCC. We first revealed a distinct immunostaining pattern of CA-IX, which was located in multiple foci in PRCC. All tumors had at least one chromosomal aberration including loss of Y, gains of 7 or 17. Gain of chromosome 17 was common in type 1; losses of chromosome 18, 11 and 8 appeared in type 2. Ultrastructurally, glycogen granules and secondary lysosomes were seen in type 1, mitochondria and smooth endoplasmic reticulum were scattered in type 2. Tumor subtype, nuclear grade, TNM stage, clear cell renal cell carcinoma (CCRCC) component and sarcomatoid elements, metastasis, CAIX expression, losses of chromosome 18 and 8 were related to poor outcome of PRCC. We conclude that the two subtypes of PRCC originate from different renal cells, and arise from partially common genetic pathways. EMA, CK7, CD10, p504s, PAX-2, PAX-8 and CA-IX are helpful markers in the differential diagnosis of PRCC. CA-IX expression, losses of chromosome 18 and 8 are new prognostic factors of PRCC.

Schwann cell glycogen selectively supports myelinated axon function.

OBJECTIVE: Interruption of energy supply to peripheral axons is a cause of axon loss. We determined whether glycogen was present in mammalian peripheral nerve, and whether it supported axon conduction during aglycemia. METHODS: We used biochemical assay and electron microscopy to determine the presence of glycogen, and electrophysiology to monitor axon function. RESULTS: Glycogen was present in sciatic nerve, its concentration varying directly with ambient glucose. Electron microscopy detected glycogen granules primarily in myelinating Schwann cell cytoplasm, and these diminished after exposure to aglycemia. During aglycemia, conduction failure in large myelinated axons (A fibers) mirrored the time course of glycogen loss. Latency to compound action potential (CAP) failure was directly related to nerve glycogen content at aglycemia onset. Glycogen did not benefit the function of slow-conducting, small-diameter unmyelinated axons (C fibers) during aglycemia. Blocking glycogen breakdown pharmacologically accelerated CAP failure during aglycemia in A fibers, but not in C fibers. Lactate was as effective as glucose in supporting sciatic nerve function, and was continuously released into the extracellular space in the presence of glucose and fell rapidly during aglycemia. INTERPRETATION: Our findings indicated that glycogen is present in peripheral nerve, primarily in myelinating Schwann cells, and exclusively supports large-diameter, myelinated axon conduction during aglycemia. Available evidence suggests that peripheral nerve glycogen breaks down during aglycemia and is passed, probably as lactate, to myelinated axons to support function. Unmyelinated axons are not protected by glycogen and are more vulnerable to dysfunction during periods of hypoglycemia. .

Thymomas with prominent signet ring cell-like features: a clinicopathologic and immunohistochemical study of 10 cases.

Ten cases of an unusual growth pattern of thymomas are presented. The patients were 8 men and 2 women between the ages of 43 and 62 years. Clinically, 6 patients presented with symptoms of chest pain, cough, and shortness of breath, whereas 4 patients were asymptomatic. Surgical resection of the mediastinal mass was performed in all patients obtaining tumors that varied in size from 4 to 11 cm in greatest dimension. Grossly, the tumors were described as round and well defined, which, at cut surface, showed a firm consistency with a slight lobulated appearance. Areas of necrosis and/or hemorrhage were not present. Histologically, all the tumors showed similar growth pattern characterized by the presence of cells arranged in small cords dissecting fibroconnective tissue and, in some areas, resembling "signet ring" cells. Mitotic activity was not present. Using the Masaoka staging system, 6 cases were in stage I, and 4 cases were in stage II. Histochemical stains for periodic-acid Schiff stain with diastase and mucicarmine were negative for intracytoplasmic mucin. Immunohistochemical studies for CAM5.2 and cytokeratin 5/6 showed a strong positive reaction, whereas thyroid transcription factor 1, epithelial membrane antigen, calretinin, α-fetoprotein, and CD31 were all negative. Follow-up information obtained for 7 patients between 1 and 12 years showed that all these patients are alive and well. The current cases highlight an unusual histologic growth pattern of thymomas that likely can be confused with other tumors of the anterior mediastinum that may require different treatment approaches and carry a different prognosis.

Extra-osseous Ewing sarcoma of the thyroid gland mimicking lymphoma recurrence: a case report.

Extra-osseous Ewing sarcomas/peripheral primitive neuroectodermal tumors (EOES/pPNETs) are high-grade malignant tumors found in various organs, such as the lung, skin, intestine, kidney and female genital tract; however, to the best of our knowledge, only two cases have previously been identified in the thyroid gland. We describe a case of primary EOES/PNET of the thyroid gland in a 66-year-old man with a previous history of large B cell lymphoma. During a routine follow-up examination, the patient underwent an ultrasound cervical scan showing a solid nodule of the left thyroid lobe. The fine-needle aspiration biopsy of the nodule suggested a neuroendocrine tumor. Histological and immunohistochemical examination of the surgical specimen supported a diagnosis of EOES/PNET, which was further confirmed by the demonstration of EWSR1 gene translocation by means of fluorescent in situ hybridization and by the detection of glycogen particles and neurosecretory granules by means of electron microscopy. Total body computed tomography and magnetic resonance imaging excluded the involvement of other sites, and therefore a diagnosis of primary EOES/PNET of the thyroid gland was made.This paper also discusses the main differential diagnoses, including lymphoma recurrence, other small round cell tumors (primary or metastatic), and a thyroid localization of an EWS/PNET from another organ.

Skeletal muscle glycogen content and particle size of distinct subcellular localizations in the recovery period after a high-level soccer match.

Whole muscle glycogen levels remain low for a prolonged period following a soccer match. The present study was conducted to investigate how this relates to glycogen content and particle size in distinct subcellular localizations. Seven high-level male soccer players had a vastus lateralis muscle biopsy collected immediately after and 24, 48, 72 and 120 h after a competitive soccer match. Transmission electron microscopy was used to estimate the subcellular distribution of glycogen and individual particle size. During the first day of recovery, glycogen content increased by ~60% in all subcellular localizations, but during the subsequent second day of recovery glycogen content located within the myofibrils (Intramyofibrillar glycogen, a minor deposition constituting 10-15% of total glycogen) did not increase further compared with an increase in subsarcolemmal glycogen (-7 vs. +25%, respectively, P = 0.047). Conversely, from the second to the fifth day of recovery, glycogen content increased (53%) within the myofibrils compared to no change in subsarcolemmal or intermyofibrillar glycogen (P < 0.005). Independent of location, increment in particle size preceded increment in number of particles. Intriguingly, average particle size decreased; however, in the period from 3 to 5 days after the match. These findings suggest that glycogen storage in skeletal muscle is influenced by subcellular localization-specific mechanisms, which account for an increase in number of glycogen particles located within the myofibrils in the period from 2 to 5 days after the soccer match.

Differential pattern of glycogen accumulation after protein phosphatase 1 glycogen-targeting subunit PPP1R6 overexpression, compared to PPP1R3C and PPP1R3A, in skeletal muscle cells.

BACKGROUND: PPP1R6 is a protein phosphatase 1 glycogen-targeting subunit (PP1-GTS) abundant in skeletal muscle with an undefined metabolic control role. Here PPP1R6 effects on myotube glycogen metabolism, particle size and subcellular distribution are examined and compared with PPP1R3C/PTG and PPP1R3A/G(M). RESULTS: PPP1R6 overexpression activates glycogen synthase (GS), reduces its phosphorylation at Ser-641/0 and increases the extracted and cytochemically-stained glycogen content, less than PTG but more than G(M). PPP1R6 does not change glycogen phosphorylase activity. All tested PP1-GTS-cells have more glycogen particles than controls as found by electron microscopy of myotube sections. Glycogen particle size is distributed for all cell-types in a continuous range, but PPP1R6 forms smaller particles (mean diameter 14.4 nm) than PTG (36.9 nm) and G(M) (28.3 nm) or those in control cells (29.2 nm). Both PPP1R6- and G(M)-derived glycogen particles are in cytosol associated with cellular structures; PTG-derived glycogen is found in membrane- and organelle-devoid cytosolic glycogen-rich areas; and glycogen particles are dispersed in the cytosol in control cells. A tagged PPP1R6 protein at the C-terminus with EGFP shows a diffuse cytosol pattern in glucose-replete and -depleted cells and a punctuate pattern surrounding the nucleus in glucose-depleted cells, which colocates with RFP tagged with the Golgi targeting domain of ß-1,4-galactosyltransferase, according to a computational prediction for PPP1R6 Golgi location. CONCLUSIONS: PPP1R6 exerts a powerful glycogenic effect in cultured muscle cells, more than G(M) and less than PTG. PPP1R6 protein translocates from a Golgi to cytosolic location in response to glucose. The molecular size and subcellular location of myotube glycogen particles is determined by the PPP1R6, PTG and G(M) scaffolding.

Glycogen storage diseases: a brief review and update on clinical features, genetic abnormalities, pathologic features, and treatment.

Glycogen storage diseases (GSD) affect primarily the liver, skeletal muscle, heart, and sometimes the central nervous system and the kidneys. These unique diseases are quite varied in age of onset of symptoms, morbidity, and mortality. Glycogen storage diseases are classified according to their individual enzyme deficiency. Each of these enzymes regulates synthesis or degradation of glycogen. Interestingly, there is great phenotypic variation and variable clinical courses even when a specific enzyme is altered by mutation. Depending on the specific mutation in an enzyme, a GSD patient may have a favorable or unfavorable prognosis. With neonatal or infantile forms, some GSDs lead to death within the first year of life, whereas other glycogen storage diseases are relatively asymptomatic or may cause only exercise intolerance. The paper provides a brief review and update of glycogen storage diseases, with respect to clinical features, genetic abnormalities, pathologic features, and treatment.

Human skeletal muscle glycogen utilization in exhaustive exercise: role of subcellular localization and fibre type.

Although glycogen is known to be heterogeneously distributed within skeletal muscle cells, there is presently little information available about the role of fibre types, utilization and resynthesis during and after exercise with respect to glycogen localization. Here, we tested the hypothesis that utilization of glycogen with different subcellular localizations during exhaustive arm and leg exercise differs and examined the influence of fibre type and carbohydrate availability on its subsequent resynthesis. When 10 elite endurance athletes (22 ± 1 years, VO2 max = 68 ± 5 ml kg-1 min-1, mean ± SD) performed one hour of exhaustive arm and leg exercise, transmission electron microscopy revealed more pronounced depletion of intramyofibrillar than of intermyofibrillar and subsarcolemmal glycogen. This phenomenon was the same for type I and II fibres, although at rest prior to exercise, the former contained more intramyofibrillar and subsarcolemmal glycogen than the latter. In highly glycogen-depleted fibres, the remaining small intermyofibrillar and subsarcolemmal glycogen particles were often found to cluster in groupings. In the recovery period, when the athletes received either a carbohydrate-rich meal or only water the impaired resynthesis of glycogen with water alone was associated primarily with intramyofibrillar glycogen. In conclusion, after prolonged high-intensity exercise the depletion of glycogen is dependent on subcellular localization. In addition, the localization of glycogen appears to be influenced by fibre type prior to exercise, as well as carbohydrate availability during the subsequent period of recovery. These findings provide insight into the significance of fibre type-specific compartmentalization of glycogen metabolism in skeletal muscle during exercise and subsequent recovery. .

Conditional ablation of glycogen synthase kinase 3ß in postnatal mouse kidney.

Glycogen synthase kinase (GSK)3 is a ubiquitously expressed serine/threonine kinase existing in two isoforms, namely GSK3α and GSK3ß. Aside from the long-recognized role in insulin signal transduction and glycogen biosynthesis, GSK3ß has been recently coined as a master control molecule in nuclear factor-κB activation and inflammatory kidney injury. Nevertheless, previous studies are less conclusive because they relied greatly on small molecule inhibitors, which lack selectivity and barely distinguish between the GSK3 isoforms. In addition, early embryonic lethality after global knockout of GSK3ß precludes interrogation of the biological role of GSK3ß in the adult kidney. To circumvent these issues, the Cre/loxP system was used to generate a conditional knockout mouse model in which the GSK3ß gene was specifically deleted in kidney cortical tubules at postnatal mature stage. Kidney-specific ablation of GSK3ß resulted in a phenotype no different from control littermates. Knockout mice (KO) were viable and exhibited normal development and normal kidney physiology in terms of kidney function, urine albumin excretion, and urine-concentrating ability. It is noteworthy that apart from normal glomerular and tubulointerstitial morphology, the kidneys from KO demonstrated more glycogen accumulation in the renal cortical tubules as assessed by both periodic acid-Schiff staining for light microscopy and direct biochemical assay, consistent with an elevated glycogen synthetic activity as evidenced by diminished inhibitory phosphorylation of glycogen synthase that occurred subsequent to GSK3ß ablation. This finding was further validated by electron microscopic observations of increased deposition of glycogen particles in the renal tubules of KO, suggesting that GSK3α could not fully compensate for the loss of GSK3ß in regulating glycogen metabolism in the kidney. Collectively, our study suggests that kidney-specific ablation of GSK3ß barely affects kidney function and histology under normal circumstances. Extended examinations of these KO under diseased conditions are merited to understand the role of GSK3ß in renal pathophysiology.