Featured Article: Beta cell specific pyruvate dehydrogenase alpha gene deletion results in a reduced islet number and β-cell mass postnatally

Abstract

The ability of pancreatic β-cells to undertake glucose-stimulated insulin secretion (GSIS) depends on the generation of adenosine triphosphate (ATP) within the mitochondria from pyruvate, a major rate-limiting enzyme being pyruvate dehydrogenase (PDH) complex (PDC). However, glucose metabolism also controls β-cell mass. To examine the role of PDC in the regulation of pancreatic β-cell development and maturation, we generated β-cell-targeted PDHα subunit knock-out male mice (β-PDHKO) and compared these with control males (β-PDHCT) from birth until 6-8 weeks age. Pancreas morphology, transcription factor expression, pancreatic insulin content, and circulating glucose and insulin values were compared. Compared to β-PDHCT male mice, β-PDHKO animals had significantly reduced pancreatic insulin content from birth, a lower serum insulin content from day 15, and relative hyperglycemia from day 30. Isolated islets from β-PDHKO mice demonstrated a reduced GSIS. The number of islets per pancreatic area, mean islet area, and the proportion of islet cells that were β-cells were all reduced in β-PDHKO animals. Similarly the number of insulin-immunopositive, extra-islet small endocrine cell clusters, a possible source of β-cell progenitors, was lower in β-PDHKO mice. Analysis of pancreatic expression of transcription factors responsible for β-cell lineage commitment, proliferation, and maturation, Pdx1, Neurogenin3, and NeuroD1 showed that mRNA abundance was reduced in the β-PDHKO. This demonstrates that PDC is not only required for insulin expression and glucose-stimulated secretion, but also directly influences β-cell growth and maturity, and positions glucose metabolism as a direct regulator of β-cell mass and plasticity.

Lack of mitochondria-generated acetyl-CoA by pyruvate dehydrogenase complex downregulates gene expression in the hepatic de novo lipogenic pathway

“…Mice used in the present study had a B6 genetic background, whereas mice used in our previously reported paper (6) had a mixed (129J/B6) genetic background. Earlier, we also reported some differences for ␤-cell structure and function between two pancreatic ␤-cellspecific PDCKO mouse strains (30,39). So it is not surprising that we have observed some variations in the levels of serum insulin and blood glucose of L-PDCKO mice (B6 genetic background) in the present study compared with that of the L-PDCKO mice (129J/B6 mixed genetic background), as reported previously (6).…”

“…In our previously published paper (6), we bred PDH-floxed females with a 129J genetic background with liver-specific Cre transgenic mice (C57BL/6J genetic background), creating the progeny with a mixed genetic background (129J/B6). To overcome any effects of a mixed genotype on metabolic phenotype of L-PDCKO mice, the 129J PDH-floxed females were back-crossed with wild-type males (B6 genetic background) for 10 generations, as reported previously (30). The progeny of the last breeding were intrabred to derive a PDHfloxed colony with a B6 genetic background.…”

“…Animal colony maintenance and all experiments were performed in accordance with the Guide for the Use and Care of Laboratory Animals and approved by the Institutional Animal Care and Use Committee of the University at Buffalo. Mice harboring the Pdha1 flox8 allele(s) were generated as described previously (18,30). This mouse colony had a 129J genetic background.…”

“…RT-PCR reactions were performed using appropriately diluted cDNA in triplicate with 18S rRNA serving as an internal control, and gene expression levels were quantified using a CFX96 Touch RT-PCR detection system (Bio-Rad) according to the manufacturer's recommendation. Relative quantification of amplified DNA was performed using the 2 Ϫ⌬⌬CT method (26,30). Primers used for gene expression analysis are presented in Table 1.…”

“…Generation of the systemic null mutation in male mice proved to be lethal at an early embryonic stage. However, tissue-specific (except the brain) deletion of the Pdha1 gene permitted both pre-and postnatal development and growth of male mice for metabolic studies (6,30,38,39). Earlier, we generated liver-specific deletion of the Pdha1 gene in male mice (L-PDCKO) to investigate its impact on lipid biosynthesis from glucose in the liver (6).…”