Description
Pre-diabetes, a risk factor for type 2 diabetes development, leads to metabolic changes at testicular level. Peroxisome
proliferator-activated receptor γ coactivator 1α(PGC-1α) and Sirtuin 3 (Sirt3) are pivotal inmitochondrial
function. We hypothesized that pre-diabetes disrupts testicular PGC-1α/Sirt3 axis, compromising testicular
mitochondrial function. Using a high-energy-diet induced pre-diabetic rat model, we evaluated testicular levels
of PGC-1α and its downstream targets, nuclear respiratory factors 1 (NRF-1) and 2 (NRF-2),mitochondrial transcription
factor A (TFAM) and Sirt3.We also assessedmitochondrial DNA (mtDNA) content, mitochondrial function,
energy levels and oxidative stress parameters. Protein levels were quantified by Western Blot, mtDNA
contentwas determined by qPCR.Mitochondrial complex activity and oxidative stress parameterswere spectrophotometrically
evaluated. Adenine nucleotide levels, adenosine and its metabolites (inosine and hypoxanthine)
were determined by reverse-phase HPLC.
Pre-diabetic rats showed increased blood glucose levels and impaired glucose tolerance. Both testicular PGC-1α
and Sirt3 levels were decreased. NRF-1, NRF-2 and TFAM were not altered. Testicular mtDNA content was
decreased. Mitochondrial complex I activity was increased, whereas mitochondrial complex III activity was
decreased. Adenylate energy charge was decreased in pre-diabetic rats, as were ATP and ADP levels. Conversely,
AMP levels were increased, evidencing a decreased ATP/AMP ratio. Concerning to oxidative stress pre-diabetes
decreased testicular antioxidant capacity and increased lipid and protein oxidation. In sum, pre-diabetes compromises
testicular mitochondrial function by repressing PGC-1α/Sirt3 axis and mtDNA copy number, declining
respiratory capacity and increasing oxidative stress. This study gives newinsights into overall testicular bioenergetics
at this prodromal stage of disease. This work was supported by the Portuguese “Fundação para a
Ciência e a Tecnologia”—FCT, co-funded by FEDER via Programa
Operacional Factores de Competitividade—COMPETE/QREN (PTDC/
QUI-BIQ/121446/2010 and PEst-C/SAU/UI0709/2011). L. Rato (SFRH/
BD/72733/2010), A. I. Duarte (SFRH/BPD/26872/2006) and M. G. Alves
(SFRH/BPD/80451/2011) were financed by FCT and European Social
Fund. P. F. Oliveira was financed by FCT through FSE and POPH funds
(Programa Ciência 2008).
; Duarte, Ana I. 
