Muscle glycogen synthase isoform is responsible for testicular glycogen synthesis: Glycogen overproduction induces apoptosis in male germ cells

Villarroel‐Espíndola, Franz; Maldonado, R.; Mancilla, Héctor; Stelt, Karen Vander; Acuña, Aníbal I.; Covarrubias, Alejandra A.; López, Camila; Angulo, Constanza; Castro, Maite A.; Slebe, Juan C.; Durán, Jordi; Garcı́a-Rocha, Mar; Guinovart, Joan J.; Concha, Ilona I.

doi:10.1002/jcb.24507

Cited by 26 publications

(33 citation statements)

References 48 publications

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“…This protein acts as a hub between glycogen synthase (GS), protein phosphatase 1 and glycogen to promote glycogen synthesis [15]. This strategy has been used to successfully enhance glycogen accumulation in several tissues [16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Genetic models rule out a major role of beta cell glycogen in the control of glucose homeostasis

et al. 2016

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Aims/hypothesis Glycogen accumulation occurs in beta cells of diabetic patients and has been proposed to partly mediate glucotoxicity-induced beta cell dysfunction. However, the role of glycogen metabolism in beta cell function and its contribution to diabetes pathophysiology remain poorly understood. We investigated the function of beta cell glycogen by studying glucose homeostasis in mice with (1) defective glycogen synthesis in the pancreas; and (2) excessive glycogen accumulation in beta cells. Methods Conditional deletion of the Gys1 gene and overexpression of protein targeting to glycogen (PTG) was accomplished by Cre-lox recombination using pancreasspecific Cre lines. Glucose homeostasis was assessed by determining fasting glycaemia, insulinaemia and glucose tolerance. Beta cell mass was determined by morphometry. Glycogen was detected histologically by periodic acidSchiff's reagent staining. Isolated islets were used for the determination of glycogen and insulin content, insulin secretion, immunoblots and gene expression assays. Results Gys1 knockout (Gys1 KO ) mice did not exhibit differences in glucose tolerance or basal glycaemia and insulinaemia relative to controls. Insulin secretion and gene expression in isolated islets was also indistinguishable between Gys1 KO and controls. Conversely, despite effective glycogen overaccumulation in islets, mice with PTG overexpression (PTG OE ) presented similar glucose tolerance to controls. However, under fasting conditions they exhibited lower glycaemia and higher insulinaemia. Importantly, neither young nor aged PTG OE mice showed differences in beta cell mass relative to age-matched controls. Finally, a high-fat diet did not reveal a beta cell-autonomous phenotype in either model. Conclusions/interpretation Glycogen metabolism is not required for the maintenance of beta cell function. Glycogen accumulation in beta cells alone is not sufficient to trigger the dysfunction or loss of these cells, or progression to diabetes.

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Section: Introductionmentioning

confidence: 99%

Genetic models rule out a major role of beta cell glycogen in the control of glucose homeostasis

et al. 2016

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“…We have suggested that our previous results observed in whole testis from the transgenic models could be explained by the pathway for glycogen synthesis (Villarroel‐Espíndola et al, ), which grows attached to the desmin and actin filaments and microtubules (Graham et al, ; Stapleton et al, ). Tight junctions and desmosome present in the blood‐testis barrier are stabilized by cytoskeleton proteins.…”

Section: Discussionmentioning

confidence: 78%

“…Previously, we have published that glycogen accumulation promotes apoptosis on male germ cells and testis degeneration (Villarroel‐Espíndola et al, ); however, the mechanism involved is not clear. We have evaluated if glucose polymer accumulation can induce a differential response in cells from the seminiferous tubules.…”

Section: Resultsmentioning

confidence: 99%

“…The histochemical studies using periodic acid‐Schiff stain and Masson stain performed to analyze the effects of glycogen accumulation in testis from transgenic animals, showed higher levels of stored glycogen and an increase on the intertubular thickness, suggesting a fibrosis condition in addition to the apoptosis of male germ cells (supplementary data). This transgenic model showed serious alterations on the architecture of the seminiferous tubules, suggesting that glycogen accumulation may promote an impairment of the blood‐testis barrier affecting directly the viability of the spermatogenic cells, or promoting differential effects on cells from the seminiferous tubules (Villarroel‐Espíndola et al, ). To analyze in vitro the observed phenotype of the transgenic mice overexpressing a super active mutant of MGS, we have proposed two main goals: (i) to determine if glycogen accumulation affects the stability and functionality of blood‐testis barrier; or (ii) to determine if glycogen accumulation induces a differential effect on cells from the seminiferous tubules.…”

Section: Resultsmentioning

confidence: 99%

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Polyglucosan Molecules Induce Mitochondrial Impairment and Apoptosis in Germ Cells Without Affecting the Integrity and Functionality of Sertoli Cells

Villarroel‐Espíndola

Tapia

González-Stegmaier

et al. 2016

Journal Cellular Physiology

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Glycogen is the main storage form of glucose; however, the accumulation of glycogen-like glucose polymers can lead to degeneration and cellular death. Previously, we reported that the accumulation of glycogen in testis of transgenic animals overexpressing a constitutively active form of glycogen synthase enhances the apoptosis of pre-meiotic male germ cells and a complete disorganization of the seminiferous tubules. Here we sought to further identify the effects of glycogen storage in cells from the seminiferous tubules and the mechanism behind the pro-apoptotic activity induced by its accumulation. Using an in vitro culture of Sertoli cells (line 42GPA9) and spermatocyte-like cells (line GC-1) expressing a superactive form of glycogen synthase or the Protein Targeting to Glycogen (PTG), we found that glycogen synthesized in both cell lines is poorly branched. In addition, the immunodetection of key molecules of apoptotic events suggests that cellular death induced by polyglucosan molecules affects GC-1 cells, but not 42GPA9 cells by mitochondrial impairment and activation of an intrinsic apoptotic pathway. Furthermore, we analyzed the effects of glycogen deposition during the establishment of an in vitro blood-testis barrier. The results using a non-permeable fluorescent molecule showed that, in conditions of over-synthesis of glycogen, 42GPA9 cells do not lose their capacity to generate an impermeable barrier and the levels of connexin43, occludin, and ZO1 proteins were not affected. These results suggest that the accumulation of polyglucosan molecules has a selective effect-triggered by the intrinsic activation of the apoptotic pathway-in germ cells without directly affecting Sertoli cells. J. Cell. Physiol. 231: 2142-2152, 2016. © 2016 Wiley Periodicals, Inc.

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“…Glycogen content in testis decreases from the first post‐natal day onwards, reaching values below 10 µg of glycogen/mg of protein after post‐natal day 10 [Villarroel‐Espíndola et al, ]. Sertoli cells are the main source of tubular glycogen when compared with germ cells [Villarroel‐Espíndola et al, ]. Nevertheless, Sertoli cell glycogen content is lower than muscle, adipose and hepatic cells.…”

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confidence: 99%

Glycogen Synthase in Sertoli Cells: More Than Glycogenesis?

Maldonado

Mancilla

Villarroel‐Espíndola

et al. 2016

J of Cellular Biochemistry

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Sertoli cell metabolism actively maintains the nutritional needs of germ cells. It has been described that after glucose incorporation in Sertoli cells, less than 1% is converted to glycogen suggesting low levels of glycogen synthase activity. Phosphorylation of muscle glycogen synthase (MGS) at serine 640 (pS640MGS) decreases its activity, and this form of the enzyme was discovered as a non-ribosomal protein that modulates the translation of a subset of transcripts in HeLa cells. The aim of our study was to functionally characterize MGS in cultured Sertoli cells, as well as to explore this new feature related to RNA molecules. We detected MGS in the cytoplasm of Sertoli cells as well as in the nuclei. The activity rates of the enzyme were extremely low indicating that MGS is expressed but almost inactive. Protein targeting to glycogen (PTG) overexpression was performed to activate MGS by dephosphorylation. PTG induced glycogen synthesis massively, confirming that this enzyme is present but inactive. This finding correlates with high levels of pS640MGS, which were assayed by phosphatase treatment. To explore a putative new function for MGS in Sertoli cells, we performed RNA immunoprecipitation coupled to microarray studies. The results revealed that MGS co-immunoprecipitated with the several mRNAs and also rRNAs. These findings indicate that MGS is expressed Sertoli cells but in an inactive form, and also support a possibly novel feature of this metabolic enzyme associated with RNA-related molecules. J. Cell. Biochem. 117: 2597-2607, 2016. © 2016 Wiley Periodicals, Inc.

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Muscle glycogen synthase isoform is responsible for testicular glycogen synthesis: Glycogen overproduction induces apoptosis in male germ cells

Cited by 26 publications

References 48 publications

Genetic models rule out a major role of beta cell glycogen in the control of glucose homeostasis

Genetic models rule out a major role of beta cell glycogen in the control of glucose homeostasis

Polyglucosan Molecules Induce Mitochondrial Impairment and Apoptosis in Germ Cells Without Affecting the Integrity and Functionality of Sertoli Cells

Glycogen Synthase in Sertoli Cells: More Than Glycogenesis?

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