Regulation of ATP hydrolase activity of the F0-F1 complex of rat-liver mitochondria during early hepatic regeneration

Enhanced PRL-1 expression in placenta-derived mesenchymal stem cells accelerates hepatic function via mitochondrial dynamics in a cirrhotic rat model

BACKGROUND

Placenta-derived mesenchymal stem cells (PD-MSCs) have been highlighted as an alternative cell therapy agent that has become a next-generation stem cell treatment. Phosphatase of regenerating liver-1 (PRL-1), an immediate early gene, plays a critical role during liver regeneration. Here, we generated enhanced PRL-1 in PD-MSCs (PD-MSCs^PRL-1, PRL-1+) using lentiviral and nonviral gene delivery systems and investigated mitochondrial functions by PD-MSC^PRL-1 transplantation for hepatic functions in a rat bile duct ligation (BDL) model.

METHODS

PD-MSCs^PRL-1 were generated by lentiviral and nonviral AMAXA gene delivery systems and analyzed for their characteristics and mitochondrial metabolic functions. Liver cirrhosis was induced in Sprague-Dawley (SD) rats using common BDL for 10 days. PKH67+ naïve and PD-MSCs^PRL-1 using a nonviral sysyem (2 × 10⁶ cells/animal) were intravenously administered into cirrhotic rats. The animals were sacrificed at 1, 2, 3, and 5 weeks after transplantation and engraftment of stem cells, and histopathological analysis and hepatic mitochondrial functions were performed.

RESULTS

PD-MSCs^PRL-1 were successfully generated using lentiviral and nonviral AMAXA systems and maintained characteristics similar to those of naïve cells. Compared with naïve cells, PD-MSCs^PRL-1 improved respirational metabolic states of mitochondria. In particular, mitochondria in PD-MSCs^PRL-1 generated by the nonviral AMAXA system showed a significant increase in the respirational metabolic state, including ATP production and mitochondrial biogenesis (*p < 0.05). Furthermore, transplantation of PD-MSCs^PRL-1 using a nonviral AMAXA system promoted engraftment into injured target liver tissues of a rat BDL cirrhotic model and enhanced the metabolism of mitochondria via increased mtDNA and ATP production, thereby improving therapeutic efficacy.

CONCLUSIONS

Our findings will further our understanding of the therapeutic mechanism of enhanced MSCs and provide useful data for the development of next-generation MSC-based cell therapy and therapeutic strategies for regenerative medicine in liver disease.

Function and expression study uncovered hepatocyte plasma membrane ecto-ATP synthase as a novel player in liver regeneration

ATP synthase, canonically mitochondrially located, is reported to be ectopically expressed on the plasma membrane outer face of several cell types. We analysed, for the first time, the expression and catalytic activities of the ecto- and mitochondrial ATP synthase during liver regeneration. Liver regeneration was induced in rats by two-thirds partial hepatectomy. The protein level and the ATP synthase and/or hydrolase activities of the hepatocyte ecto- and mitochondrial ATP synthase were analysed on freshly isolated hepatocytes and mitochondria from control, sham-operated and partial hepatectomized rats. During the priming phase of liver regeneration, 3 h after partial hepatectomy, liver mitochondria showed a marked lowering of the ATP synthase protein level that was reflected in the impairment of both ATP synthesis and hydrolysis. The ecto-ATP synthase level, in 3 h partial hepatectomized hepatocytes, was decreased similarly to the level of the mitochondrial ATP synthase, associated with a lowering of the ecto-ATP hydrolase activity coupled to proton influx. Noteworthily, the ecto-ATP synthase activity coupled to proton efflux was completely inhibited in 3 h partial hepatectomized hepatocytes, even in the presence of a marked intracellular acidification that would sustain it as in control and sham-operated hepatocytes. At the end of the liver regeneration, 7 days after partial hepatectomy, the level and the catalytic activities of the ecto- and mitochondrial ATP synthase reached the control and sham-operated values. The specific modulation of hepatocyte ecto-ATP synthase catalytic activities during liver regeneration priming phase may modulate the extracellular ADP/ATP levels and/or proton influx/efflux trafficking, making hepatocyte ecto-ATP synthase a candidate for a novel player in the liver regeneration process.

Changes in mitochondrial adenine nucleotides and in permeability transition in two models of rat liver regeneration

Although enhanced phosphorylative activity can be a requisite for later DNA synthesis during liver regeneration (LR), mitochondrial generation of reactive oxygen species could lead to altered mitochondrial membrane permeability during the prereplicative phase of LR. Therefore, the role of mitochondrial permeability transition (MPT) was evaluated during rat LR, induced by either partial hepatectomy (PH) or after CCl(4) administration. Parameters indicative of mitochondrial function and membrane potentials, those of oxidative stress, and in vivo changes of the intramitochondrial pool of adenine nucleotides were determined. Twelve hours after PH, mitochondrial oxidative and phosphorylative activities and adenosine diphosphate (ADP) content were increased, reaching a maximal peak at 24 hours after surgery (maximal DNA synthesis). Parameters suggestive of oxidant stress were enhanced, but mitochondrial volume and membrane electrical potential remained unaltered. Interestingly, moderate mitochondrial swelling and depolarization were found at later post-PH times (72 hours). In CCl(4)-treated animals, it was found that an active liver cell necrosis delayed mitotic activity and mitochondrial uncoupled respiration. Starting 12 hours after CCl(4) intoxication, a drastic increase of inorganic phosphate occurred within swollen and strongly depolarized mitochondria, suggesting changes in the MPT. Despite expression of messenger RNA (mRNA) for mitochondrial transcription, factor A showed a similar time course in both experimental models. The so-called augmenter liver regeneration was found significantly elevated only in PH rats. In conclusion, onset of MPT could be associated with cell necrosis and inflammation after CCl(4) treatment, whereas this mitochondrial event could constitute a putative effector mechanism, through which growth or inflammatory factors inhibiting cell proliferation could initiate LR termination.

In vivo 31P NMR spectroscopic changes during liver regeneration

Liver regeneration following partial hepatectomy involves rapid cell division 24 to 72 hr postresection. This cell division would necessarily involve changes in intracellular energy stores and cell membrane phospholipid precursors. In tumor models 31P nuclear magnetic resonance (NMR) has been shown to identify intracellular substrate changes associated with cell growth. The ability to monitor early changes in adenosine triphosphate (ATP), inorganic orthophosphate (Pi), phosphomonoesters (PME), or phosphodiesters (PDE) after liver resection could indicate the intracellular changes necessary for hepatocellular regeneration. In vivo 31P NMR scans of the liver were performed in both normal rats and in rats at 24, 48, 72, and 120 hr after 70% hepatectomy. At 48 hr, total ATP fell to 18.9% (P less than 0.05) and both Pi/beta-ATP and PME/beta-ATP were significantly elevated (P less than 0.01) from controls. These changes correlate with the known mitotic peak in the rat following hepatectomy. We conclude that in vivo 31P NMR is a potentially valuable tool for studying hepatic regeneration. The data also suggest that hepatocellular regeneration may be critically dependent on cellular ATP stores.