Extrahepatic cholestasis is characterized by bile acid accumulation in the liver, associated with loss of mitochondrial membrane potential, respiratory inefficiency, decreased ATP production and increased generation of reactive oxygen species.

Aim: 

To assess the regulation of mitochondrial biogenesis in rat liver during chronic cholestasis.

Methods: 

28 days after surgery, livers from 3 groups of rats (BDL, bile duct ligated; SHAM, control; PAIR-FED to BDL animals) were collected and the expression of NRF-1, Tfam and GABP-alpha was assessed by RT-PCR and western blotting. The expression of mitochondrial chaperones Hsp70 and Hsp60, cyt-c, HVDAC-1 and Tomm20, 40 and 70 was determined by western blotting; mitochondrial-DNA/nuclear-DNA ratio (mtDNA/nDNA) was measured by qPCR.

Results: 

GABP-alpha, and NRF-1 were slightly increased in BDL vs. PAIR-FED, but Tfam was not. Tfam import into the mitochondria was impaired only in BDL, but not the import of cyt-c or HVDAC-1. Hsp60 slightly decreased in BDL vs. PAIR-FED, but Hsp-70 was 4 fold increased in BDL. Immunoblotting for Hsp70 in mitochondria preparations showed a failure in the import only in BDL. Tomm20 was unchanged, Tomm40 was increased and Tomm70 decreased in BDL vs. PAIR-FED. mtDNA/nDNA was decreased in BDL.

Conclusions: 

Mitochondrial biogenesis is impaired in BDL animals due to import failure of the matrix-directed mitochondrial proteins Tfam and Hsp70. Compensatory mechanisms, such as an increase in Tomm40 despite the loss in Tomm70 can maintain the import of some proteins different from Tfam and Hsp-70. Consequently, mtDNA maintenance is largely compromised in rats with chronic extrahepatic cholestasis.

Supported by Grant CSD-2007-0020 from M.C.I.