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Mice lacking thyroid hormone receptor Beta show enhanced apoptosis and delayed liver commitment for proliferation after partial hepatectomy.

López-Fontal R, Zeini M, Través PG, Gómez-Ferrería M, Aranda A, Sáez GT, Cerdá C, Martín-Sanz P, Hortelano S, Boscá L - PLoS ONE (2010)

Bottom Line: Pharmacologically induced hypothyroidism yielded similar results.Loss of TR activity was associated with enhanced nitrosative stress in the liver remnant, due to an increase in the activity of the nitric oxide synthase (NOS) 2 and 3, caused by a transient decrease in the concentration of asymmetric dimethylarginine (ADMA), a potent NOS inhibitor.Taken together, these results indicate that TRbeta contributes significantly to the rapid initial round of hepatocyte proliferation following PH, and improves the survival of the regenerating liver at later times.

View Article: PubMed Central - PubMed

Affiliation: Centro Nacional de Investigaciones Cardiovasculares, Madrid, Spain.

ABSTRACT

Background: The role of thyroid hormones and their receptors (TR) during liver regeneration after partial hepatectomy (PH) was studied using genetic and pharmacologic approaches. Roles in liver regeneration have been suggested for T3, but there is no clear evidence distinguishing the contribution of increased amounts of T3 from the modulation by unoccupied TRs.

Methodology/principal findings: Mice lacking TRalpha1/TRbeta or TRbeta alone fully regenerated liver mass after PH, but showed delayed commitment to the initial round of hepatocyte proliferation and transient but intense apoptosis at 48h post-PH, affecting approximately 30% of the remaining hepatocytes. Pharmacologically induced hypothyroidism yielded similar results. Loss of TR activity was associated with enhanced nitrosative stress in the liver remnant, due to an increase in the activity of the nitric oxide synthase (NOS) 2 and 3, caused by a transient decrease in the concentration of asymmetric dimethylarginine (ADMA), a potent NOS inhibitor. This decrease in the ADMA levels was due to the presence of a higher activity of dimethylarginineaminohydrolase-1 (DDAH-1) in the regenerating liver of animals lacking TRalpha1/TRbeta or TRbeta. DDAH-1 expression and activity was paralleled by the activity of FXR, a transcription factor involved in liver regeneration and up-regulated in the absence of TR.

Conclusions/significance: We report that TRs are not required for liver regeneration; however, hypothyroid mice and TRbeta- or TRalpha1/TRbeta-deficient mice exhibit a delay in the restoration of liver mass, suggesting a specific role for TRbeta in liver regeneration. Altered regenerative responses are related with a delay in the expression of cyclins D1 and E, and the occurrence of liver apoptosis in the absence of activated TRbeta that can be prevented by administration of NOS inhibitors. Taken together, these results indicate that TRbeta contributes significantly to the rapid initial round of hepatocyte proliferation following PH, and improves the survival of the regenerating liver at later times.

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TRβ inhibits apoptosis in regenerating liver.(A) TUNEL staining of cells undergoing apoptosis in regenerating liver (green). Liver sections were obtained at the indicated times after PH. The mean (n = 5 sections) of TUNEL positive cells per 100 nuclei (blue; TO-PRO-3 staining) is given at 48 h. (B) Caspase 3 activity was determined fluorometrically in liver extracts obtained at the indicated times after PH, and expressed vs. the activity of sham samples at 0h. (C) Alternatively, liver sections were stained with eosin/hematoxylin or Nile red to visualize lipid bodies. (D,E) Intrahepatic levels of cholesterol and triglycerides determined in liver extracts obtained at the indicated times after PH. Results show means ± SD of 6 animals per condition (B,D,E) or sections from a representative experiment of three (A,C). *P<0.05 vs. the WT condition.
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pone-0008710-g003: TRβ inhibits apoptosis in regenerating liver.(A) TUNEL staining of cells undergoing apoptosis in regenerating liver (green). Liver sections were obtained at the indicated times after PH. The mean (n = 5 sections) of TUNEL positive cells per 100 nuclei (blue; TO-PRO-3 staining) is given at 48 h. (B) Caspase 3 activity was determined fluorometrically in liver extracts obtained at the indicated times after PH, and expressed vs. the activity of sham samples at 0h. (C) Alternatively, liver sections were stained with eosin/hematoxylin or Nile red to visualize lipid bodies. (D,E) Intrahepatic levels of cholesterol and triglycerides determined in liver extracts obtained at the indicated times after PH. Results show means ± SD of 6 animals per condition (B,D,E) or sections from a representative experiment of three (A,C). *P<0.05 vs. the WT condition.

Mentions: Analysis of apoptosis by TUNEL in regenerating liver identified a transient peak at 48 h after PH in TRα1/TRβ KO and MMI-treated mice (Fig. 3A). This apoptotic response was accompanied by an increased caspase 3 activity in samples of the remnant liver at 48 h (Fig. 3B). However, other processes relevant to the regenerative response, such as steatosis, evaluated by the accumulation of Nile red positive droplets (Fig. 3C) and liver cholesterol and triglyceride content (Fig. 3D–E), appeared to be little affected by the lack of functional TRs, although there was a moderate but statistically significant increase (p<0.05) in liver cholesterol and triglycerides in TRα1/TRβ KO animals at 48 h.


Mice lacking thyroid hormone receptor Beta show enhanced apoptosis and delayed liver commitment for proliferation after partial hepatectomy.

López-Fontal R, Zeini M, Través PG, Gómez-Ferrería M, Aranda A, Sáez GT, Cerdá C, Martín-Sanz P, Hortelano S, Boscá L - PLoS ONE (2010)

TRβ inhibits apoptosis in regenerating liver.(A) TUNEL staining of cells undergoing apoptosis in regenerating liver (green). Liver sections were obtained at the indicated times after PH. The mean (n = 5 sections) of TUNEL positive cells per 100 nuclei (blue; TO-PRO-3 staining) is given at 48 h. (B) Caspase 3 activity was determined fluorometrically in liver extracts obtained at the indicated times after PH, and expressed vs. the activity of sham samples at 0h. (C) Alternatively, liver sections were stained with eosin/hematoxylin or Nile red to visualize lipid bodies. (D,E) Intrahepatic levels of cholesterol and triglycerides determined in liver extracts obtained at the indicated times after PH. Results show means ± SD of 6 animals per condition (B,D,E) or sections from a representative experiment of three (A,C). *P<0.05 vs. the WT condition.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2806828&req=5

pone-0008710-g003: TRβ inhibits apoptosis in regenerating liver.(A) TUNEL staining of cells undergoing apoptosis in regenerating liver (green). Liver sections were obtained at the indicated times after PH. The mean (n = 5 sections) of TUNEL positive cells per 100 nuclei (blue; TO-PRO-3 staining) is given at 48 h. (B) Caspase 3 activity was determined fluorometrically in liver extracts obtained at the indicated times after PH, and expressed vs. the activity of sham samples at 0h. (C) Alternatively, liver sections were stained with eosin/hematoxylin or Nile red to visualize lipid bodies. (D,E) Intrahepatic levels of cholesterol and triglycerides determined in liver extracts obtained at the indicated times after PH. Results show means ± SD of 6 animals per condition (B,D,E) or sections from a representative experiment of three (A,C). *P<0.05 vs. the WT condition.
Mentions: Analysis of apoptosis by TUNEL in regenerating liver identified a transient peak at 48 h after PH in TRα1/TRβ KO and MMI-treated mice (Fig. 3A). This apoptotic response was accompanied by an increased caspase 3 activity in samples of the remnant liver at 48 h (Fig. 3B). However, other processes relevant to the regenerative response, such as steatosis, evaluated by the accumulation of Nile red positive droplets (Fig. 3C) and liver cholesterol and triglyceride content (Fig. 3D–E), appeared to be little affected by the lack of functional TRs, although there was a moderate but statistically significant increase (p<0.05) in liver cholesterol and triglycerides in TRα1/TRβ KO animals at 48 h.

Bottom Line: Pharmacologically induced hypothyroidism yielded similar results.Loss of TR activity was associated with enhanced nitrosative stress in the liver remnant, due to an increase in the activity of the nitric oxide synthase (NOS) 2 and 3, caused by a transient decrease in the concentration of asymmetric dimethylarginine (ADMA), a potent NOS inhibitor.Taken together, these results indicate that TRbeta contributes significantly to the rapid initial round of hepatocyte proliferation following PH, and improves the survival of the regenerating liver at later times.

View Article: PubMed Central - PubMed

Affiliation: Centro Nacional de Investigaciones Cardiovasculares, Madrid, Spain.

ABSTRACT

Background: The role of thyroid hormones and their receptors (TR) during liver regeneration after partial hepatectomy (PH) was studied using genetic and pharmacologic approaches. Roles in liver regeneration have been suggested for T3, but there is no clear evidence distinguishing the contribution of increased amounts of T3 from the modulation by unoccupied TRs.

Methodology/principal findings: Mice lacking TRalpha1/TRbeta or TRbeta alone fully regenerated liver mass after PH, but showed delayed commitment to the initial round of hepatocyte proliferation and transient but intense apoptosis at 48h post-PH, affecting approximately 30% of the remaining hepatocytes. Pharmacologically induced hypothyroidism yielded similar results. Loss of TR activity was associated with enhanced nitrosative stress in the liver remnant, due to an increase in the activity of the nitric oxide synthase (NOS) 2 and 3, caused by a transient decrease in the concentration of asymmetric dimethylarginine (ADMA), a potent NOS inhibitor. This decrease in the ADMA levels was due to the presence of a higher activity of dimethylarginineaminohydrolase-1 (DDAH-1) in the regenerating liver of animals lacking TRalpha1/TRbeta or TRbeta. DDAH-1 expression and activity was paralleled by the activity of FXR, a transcription factor involved in liver regeneration and up-regulated in the absence of TR.

Conclusions/significance: We report that TRs are not required for liver regeneration; however, hypothyroid mice and TRbeta- or TRalpha1/TRbeta-deficient mice exhibit a delay in the restoration of liver mass, suggesting a specific role for TRbeta in liver regeneration. Altered regenerative responses are related with a delay in the expression of cyclins D1 and E, and the occurrence of liver apoptosis in the absence of activated TRbeta that can be prevented by administration of NOS inhibitors. Taken together, these results indicate that TRbeta contributes significantly to the rapid initial round of hepatocyte proliferation following PH, and improves the survival of the regenerating liver at later times.

Show MeSH
Related in: MedlinePlus