Limits...
Loss of Liver Kinase B1 (LKB1) in Beta Cells Enhances Glucose-stimulated Insulin Secretion Despite Profound Mitochondrial Defects.

Swisa A, Granot Z, Tamarina N, Sayers S, Bardeesy N, Philipson L, Hodson DJ, Wikstrom JD, Rutter GA, Leibowitz G, Glaser B, Dor Y - J. Biol. Chem. (2015)

Bottom Line: However, the full spectrum of LKB1 effects and the mechanisms involved in the secretory phenotype remain incompletely understood.Surprisingly, enhanced GSIS is seen despite profound defects in mitochondrial structure and function in LKB1-deficient β cells, expected to greatly diminish insulin secretion via the classic triggering pathway.This study shows that β cells can be manipulated to enhance GSIS to supra-normal levels even in the face of defective mitochondria and without deterioration over months.

View Article: PubMed Central - PubMed

Affiliation: From the Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.

Show MeSH

Related in: MedlinePlus

In vitro rescue of LKB1-deficient β cells.A, LKB1 mRNA levels measured by qRT-PCR in cultured wild type and βLKB islets, 48 h after infection with adenoviruses encoding wild type LKB1. n = 3 mice/condition. Cells were infected at the multiplicity of infection indicated. *, p < 0.05; **, p < 0.01; ***, p < 0.005. B, rescue of glucose-stimulated calcium influx in LKB1-deficient islets. Both the amplitude (center) and the fraction of responding cells (right) returned to normal upon LKB1 re-expression. n = 3 mice per genotype, 9–12 islets per genotype. AU, arbitrary units. C, rescue of glucose-stimulated [ATP/ADP]cyt rise in LKB1-deficient islets. Both the amplitude (center) and the fraction of responding islets (right) are improved upon LKB1 re-expression. n = 5 mice per genotype, 9–15 islets per genotype. *, p < 0.05; **, p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4543653&req=5

Figure 6: In vitro rescue of LKB1-deficient β cells.A, LKB1 mRNA levels measured by qRT-PCR in cultured wild type and βLKB islets, 48 h after infection with adenoviruses encoding wild type LKB1. n = 3 mice/condition. Cells were infected at the multiplicity of infection indicated. *, p < 0.05; **, p < 0.01; ***, p < 0.005. B, rescue of glucose-stimulated calcium influx in LKB1-deficient islets. Both the amplitude (center) and the fraction of responding cells (right) returned to normal upon LKB1 re-expression. n = 3 mice per genotype, 9–12 islets per genotype. AU, arbitrary units. C, rescue of glucose-stimulated [ATP/ADP]cyt rise in LKB1-deficient islets. Both the amplitude (center) and the fraction of responding islets (right) are improved upon LKB1 re-expression. n = 5 mice per genotype, 9–15 islets per genotype. *, p < 0.05; **, p < 0.01.

Mentions: The deletion of LKB1 in β cells in vivo is incomplete, as in most tamoxifen-inducible mouse systems. Therefore, the phenotypes analyzed here could in principle reflect either a cell autonomous, direct effect of LKB1 deletion in β cells or, alternatively, a compensatory effect in wild type β cells. We showed before that LKB1 deletion leads to improved glucose tolerance in vivo as early as 1 week after tamoxifen injection (23), strongly suggesting that the underlying mechanism is a direct enhancement of insulin secretion from LKB1-deficient β cells. In addition, a recent paper has documented enhanced secretion in min6 cells with LKB1 knockdown (47), further supporting this conclusion. To examine whether the energy metabolism phenotype (defective mitochondrial function) also acts in a cell autonomous manner, we reintroduced wild type LKB1 via adenoviral infection to cultured LKB1-deficient islets. Within 48 h of infection, LKB1 levels in mutant islets were restored (Fig. 6A), and both calcium influx and ATP levels were restored to near-normal levels (Fig. 6, B and C). These results indicate that the defects in energy metabolism in LKB1-deficient islets are a direct effect of LKB1 loss in β cells rather than an indirect compensatory mechanism.


Loss of Liver Kinase B1 (LKB1) in Beta Cells Enhances Glucose-stimulated Insulin Secretion Despite Profound Mitochondrial Defects.

Swisa A, Granot Z, Tamarina N, Sayers S, Bardeesy N, Philipson L, Hodson DJ, Wikstrom JD, Rutter GA, Leibowitz G, Glaser B, Dor Y - J. Biol. Chem. (2015)

In vitro rescue of LKB1-deficient β cells.A, LKB1 mRNA levels measured by qRT-PCR in cultured wild type and βLKB islets, 48 h after infection with adenoviruses encoding wild type LKB1. n = 3 mice/condition. Cells were infected at the multiplicity of infection indicated. *, p < 0.05; **, p < 0.01; ***, p < 0.005. B, rescue of glucose-stimulated calcium influx in LKB1-deficient islets. Both the amplitude (center) and the fraction of responding cells (right) returned to normal upon LKB1 re-expression. n = 3 mice per genotype, 9–12 islets per genotype. AU, arbitrary units. C, rescue of glucose-stimulated [ATP/ADP]cyt rise in LKB1-deficient islets. Both the amplitude (center) and the fraction of responding islets (right) are improved upon LKB1 re-expression. n = 5 mice per genotype, 9–15 islets per genotype. *, p < 0.05; **, p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4543653&req=5

Figure 6: In vitro rescue of LKB1-deficient β cells.A, LKB1 mRNA levels measured by qRT-PCR in cultured wild type and βLKB islets, 48 h after infection with adenoviruses encoding wild type LKB1. n = 3 mice/condition. Cells were infected at the multiplicity of infection indicated. *, p < 0.05; **, p < 0.01; ***, p < 0.005. B, rescue of glucose-stimulated calcium influx in LKB1-deficient islets. Both the amplitude (center) and the fraction of responding cells (right) returned to normal upon LKB1 re-expression. n = 3 mice per genotype, 9–12 islets per genotype. AU, arbitrary units. C, rescue of glucose-stimulated [ATP/ADP]cyt rise in LKB1-deficient islets. Both the amplitude (center) and the fraction of responding islets (right) are improved upon LKB1 re-expression. n = 5 mice per genotype, 9–15 islets per genotype. *, p < 0.05; **, p < 0.01.
Mentions: The deletion of LKB1 in β cells in vivo is incomplete, as in most tamoxifen-inducible mouse systems. Therefore, the phenotypes analyzed here could in principle reflect either a cell autonomous, direct effect of LKB1 deletion in β cells or, alternatively, a compensatory effect in wild type β cells. We showed before that LKB1 deletion leads to improved glucose tolerance in vivo as early as 1 week after tamoxifen injection (23), strongly suggesting that the underlying mechanism is a direct enhancement of insulin secretion from LKB1-deficient β cells. In addition, a recent paper has documented enhanced secretion in min6 cells with LKB1 knockdown (47), further supporting this conclusion. To examine whether the energy metabolism phenotype (defective mitochondrial function) also acts in a cell autonomous manner, we reintroduced wild type LKB1 via adenoviral infection to cultured LKB1-deficient islets. Within 48 h of infection, LKB1 levels in mutant islets were restored (Fig. 6A), and both calcium influx and ATP levels were restored to near-normal levels (Fig. 6, B and C). These results indicate that the defects in energy metabolism in LKB1-deficient islets are a direct effect of LKB1 loss in β cells rather than an indirect compensatory mechanism.

Bottom Line: However, the full spectrum of LKB1 effects and the mechanisms involved in the secretory phenotype remain incompletely understood.Surprisingly, enhanced GSIS is seen despite profound defects in mitochondrial structure and function in LKB1-deficient β cells, expected to greatly diminish insulin secretion via the classic triggering pathway.This study shows that β cells can be manipulated to enhance GSIS to supra-normal levels even in the face of defective mitochondria and without deterioration over months.

View Article: PubMed Central - PubMed

Affiliation: From the Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.

Show MeSH
Related in: MedlinePlus