Limits...
Forced expression of fibroblast growth factor 21 reverses the sustained impairment of liver regeneration in hPPARα(PAC) mice due to dysregulated bile acid synthesis.

Liu HX, Hu Y, French SW, Gonzalez FJ, Wan YJ - Oncotarget (2015)

Bottom Line: The liver-to-body weight ratios did not recover even 3 months after PH in hPPARα(PAC).Forced FGF21 expression in partial hepatectomized hPPARα(PAC) reduced hepatic steatosis, prevented focal necrosis, and restored liver mass.In addition, FGF21 can compensate for the reduced ability of human PPARα in stimulating liver regeneration, which suggests the potential application of FGF21 in promoting hepatic growth in injured and steatotic livers in humans.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Pathology and Laboratory Medicine, University of California, Davis, Sacramento, CA, USA.

ABSTRACT
Peroxisome proliferator activated receptor α (PPARα) stimulates hepatocellular proliferation is species-specific. Activation of mouse, but not human, PPARα induces hepatocellular proliferation, hepatomegaly, and liver cancer. Here we tested the hypothesis that human and mouse PPARα affects liver regeneration differentially. PPARα-humanized mice (hPPARα(PAC)) were similar to wild type mice in responding to fasting-induced PPARα signaling. However, these mouse livers failed to regenerate in response to partial hepatectomy (PH). The liver-to-body weight ratios did not recover even 3 months after PH in hPPARα(PAC). The mouse PPARα-mediated down-regulation of let-7c was absent in hPPARα(PAC), which might partially be responsible for impaired proliferation. After PH, hPPARα(PAC) displayed steatosis, necrosis, and inflammation mainly in periportal zone 1, which suggested bile-induced toxicity. Quantification of hepatic bile acids (BA) revealed BA overload with increased hydrophobic BA in hPPARα(PAC). Forced FGF21 expression in partial hepatectomized hPPARα(PAC) reduced hepatic steatosis, prevented focal necrosis, and restored liver mass. Compared to mouse PPARα, human PPARα has a reduced capacity to regulate metabolic pathways required for liver regeneration. In addition, FGF21 can compensate for the reduced ability of human PPARα in stimulating liver regeneration, which suggests the potential application of FGF21 in promoting hepatic growth in injured and steatotic livers in humans.

No MeSH data available.


Related in: MedlinePlus

The induction of hepatic cell cycle genes is diminished in hPPARαPAC mice after PHExperiments were performed based on the description in Figure legend 2. Hepatic gene expression of Pcna, Cyclin A, Cyclin B/Cdk1, Cyclin D/Cdk6, and Cyclin E was studied by qPCR in WT and hPPARαPAC mouse livers after PH (A-G). Western blot analysis of CYCLIN D and E protein levels in WT and hPPARαPAC livers after PH (H). All values represent mean ± standard deviation, n = 5; * p<0.05, student's t test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4496390&req=5

Figure 3: The induction of hepatic cell cycle genes is diminished in hPPARαPAC mice after PHExperiments were performed based on the description in Figure legend 2. Hepatic gene expression of Pcna, Cyclin A, Cyclin B/Cdk1, Cyclin D/Cdk6, and Cyclin E was studied by qPCR in WT and hPPARαPAC mouse livers after PH (A-G). Western blot analysis of CYCLIN D and E protein levels in WT and hPPARαPAC livers after PH (H). All values represent mean ± standard deviation, n = 5; * p<0.05, student's t test.

Mentions: PH was performed in WT and hPPARαPAC mice, and livers were collected on 1 day up to 3 months post-surgery. The liver-to-body weight ratio of WT and hPPARαPAC mice (without surgery) ranged from 4.2-4.5% and no statistical difference was found between the groups (data not shown). After PH, the liver-to-body weight ratio restored within 7 days in WT mice, whereas in hPPARαPAC mice, the liver-to-body weight ratios were reduced at all studied time points compared to WT controls. The liver-to-body weight ratio was 3.6% from 7 days to 3 months after PH in hPPARαPAC mice indicating that these mice failed to restore their original liver mass and normal liver regeneration was disrupted (Fig. 2A). WT livers, compared with hPPARαPAC livers, exhibited greater hepatocellular proliferation, as shown by increased numbers of Ki67-positive hepatocytes after PH (Fig. 2B). Hematoxylin and eosin (H&E) staining revealed transient accumulation of hepatic lipids in WT mice 1.5 days after PH, which is likely essential for liver regeneration [3]. Two days after PH, lipid accumulation was diminished in WT livers (Fig. 2C). Representative images of hPPARαPAC liver sections harvested 1.5 and 2 days post-PH indicate that hPPARαPAC mice had lipid deposition (Fig. 2C). hPPARαPAC mice also showed 3 to 7-fold increase in hepatic triglyceride levels 1.5 and 2 days after PH (Fig. 2C). Furthermore, the increased cell proliferation found in WT mice 1.5-2 day after PH were accompanied by higher expression levels of proliferating cell nuclear antigen (Pcna), Cyclin A, Cyclin B/Cyclin-dependent kinase (Cdk) 1 complex, Cyclin D/Cdk6 complex, and Cyclin E mRNAs (Fig. 3A-G). However, such inductions were delayed and reduced in hPPARαPAC mouse livers. Moreover, Western blots indicated that CYCLIN D and E proteins were induced after PH in WT mouse livers, but not in hPPARαPAC livers (Fig. 3H). In addition, the expression of PPARα target let-7c, which promotes cell cycle arrest by targeting c-Myc mRNA [20], was studied to compare the differences between mouse and human PPARα in regulating liver regeneration. A temporal pattern of down-regulated let-7c was observed in regenerating WT mice. At most studied time points, except 3 days after PH, let-7c levels were higher in hPPARαPAC than WT mouse livers (Fig. 4A). Accordingly, c-Myc mRNA levels were lower in hPPARαPAC than WT mouse livers 1, 2, and 5 days after PH (Fig. 4B).


Forced expression of fibroblast growth factor 21 reverses the sustained impairment of liver regeneration in hPPARα(PAC) mice due to dysregulated bile acid synthesis.

Liu HX, Hu Y, French SW, Gonzalez FJ, Wan YJ - Oncotarget (2015)

The induction of hepatic cell cycle genes is diminished in hPPARαPAC mice after PHExperiments were performed based on the description in Figure legend 2. Hepatic gene expression of Pcna, Cyclin A, Cyclin B/Cdk1, Cyclin D/Cdk6, and Cyclin E was studied by qPCR in WT and hPPARαPAC mouse livers after PH (A-G). Western blot analysis of CYCLIN D and E protein levels in WT and hPPARαPAC livers after PH (H). All values represent mean ± standard deviation, n = 5; * p<0.05, student's t test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496390&req=5

Figure 3: The induction of hepatic cell cycle genes is diminished in hPPARαPAC mice after PHExperiments were performed based on the description in Figure legend 2. Hepatic gene expression of Pcna, Cyclin A, Cyclin B/Cdk1, Cyclin D/Cdk6, and Cyclin E was studied by qPCR in WT and hPPARαPAC mouse livers after PH (A-G). Western blot analysis of CYCLIN D and E protein levels in WT and hPPARαPAC livers after PH (H). All values represent mean ± standard deviation, n = 5; * p<0.05, student's t test.
Mentions: PH was performed in WT and hPPARαPAC mice, and livers were collected on 1 day up to 3 months post-surgery. The liver-to-body weight ratio of WT and hPPARαPAC mice (without surgery) ranged from 4.2-4.5% and no statistical difference was found between the groups (data not shown). After PH, the liver-to-body weight ratio restored within 7 days in WT mice, whereas in hPPARαPAC mice, the liver-to-body weight ratios were reduced at all studied time points compared to WT controls. The liver-to-body weight ratio was 3.6% from 7 days to 3 months after PH in hPPARαPAC mice indicating that these mice failed to restore their original liver mass and normal liver regeneration was disrupted (Fig. 2A). WT livers, compared with hPPARαPAC livers, exhibited greater hepatocellular proliferation, as shown by increased numbers of Ki67-positive hepatocytes after PH (Fig. 2B). Hematoxylin and eosin (H&E) staining revealed transient accumulation of hepatic lipids in WT mice 1.5 days after PH, which is likely essential for liver regeneration [3]. Two days after PH, lipid accumulation was diminished in WT livers (Fig. 2C). Representative images of hPPARαPAC liver sections harvested 1.5 and 2 days post-PH indicate that hPPARαPAC mice had lipid deposition (Fig. 2C). hPPARαPAC mice also showed 3 to 7-fold increase in hepatic triglyceride levels 1.5 and 2 days after PH (Fig. 2C). Furthermore, the increased cell proliferation found in WT mice 1.5-2 day after PH were accompanied by higher expression levels of proliferating cell nuclear antigen (Pcna), Cyclin A, Cyclin B/Cyclin-dependent kinase (Cdk) 1 complex, Cyclin D/Cdk6 complex, and Cyclin E mRNAs (Fig. 3A-G). However, such inductions were delayed and reduced in hPPARαPAC mouse livers. Moreover, Western blots indicated that CYCLIN D and E proteins were induced after PH in WT mouse livers, but not in hPPARαPAC livers (Fig. 3H). In addition, the expression of PPARα target let-7c, which promotes cell cycle arrest by targeting c-Myc mRNA [20], was studied to compare the differences between mouse and human PPARα in regulating liver regeneration. A temporal pattern of down-regulated let-7c was observed in regenerating WT mice. At most studied time points, except 3 days after PH, let-7c levels were higher in hPPARαPAC than WT mouse livers (Fig. 4A). Accordingly, c-Myc mRNA levels were lower in hPPARαPAC than WT mouse livers 1, 2, and 5 days after PH (Fig. 4B).

Bottom Line: The liver-to-body weight ratios did not recover even 3 months after PH in hPPARα(PAC).Forced FGF21 expression in partial hepatectomized hPPARα(PAC) reduced hepatic steatosis, prevented focal necrosis, and restored liver mass.In addition, FGF21 can compensate for the reduced ability of human PPARα in stimulating liver regeneration, which suggests the potential application of FGF21 in promoting hepatic growth in injured and steatotic livers in humans.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Pathology and Laboratory Medicine, University of California, Davis, Sacramento, CA, USA.

ABSTRACT
Peroxisome proliferator activated receptor α (PPARα) stimulates hepatocellular proliferation is species-specific. Activation of mouse, but not human, PPARα induces hepatocellular proliferation, hepatomegaly, and liver cancer. Here we tested the hypothesis that human and mouse PPARα affects liver regeneration differentially. PPARα-humanized mice (hPPARα(PAC)) were similar to wild type mice in responding to fasting-induced PPARα signaling. However, these mouse livers failed to regenerate in response to partial hepatectomy (PH). The liver-to-body weight ratios did not recover even 3 months after PH in hPPARα(PAC). The mouse PPARα-mediated down-regulation of let-7c was absent in hPPARα(PAC), which might partially be responsible for impaired proliferation. After PH, hPPARα(PAC) displayed steatosis, necrosis, and inflammation mainly in periportal zone 1, which suggested bile-induced toxicity. Quantification of hepatic bile acids (BA) revealed BA overload with increased hydrophobic BA in hPPARα(PAC). Forced FGF21 expression in partial hepatectomized hPPARα(PAC) reduced hepatic steatosis, prevented focal necrosis, and restored liver mass. Compared to mouse PPARα, human PPARα has a reduced capacity to regulate metabolic pathways required for liver regeneration. In addition, FGF21 can compensate for the reduced ability of human PPARα in stimulating liver regeneration, which suggests the potential application of FGF21 in promoting hepatic growth in injured and steatotic livers in humans.

No MeSH data available.


Related in: MedlinePlus