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

Area of Science:

• Hepatology
• Endocrinology
• Molecular Biology

Background:

• Thyroid hormones and their receptors (TRs) are implicated in liver regeneration.
• Previous studies lacked clear evidence distinguishing the roles of T3 levels versus unoccupied TRs.

Purpose of the Study:

• To investigate the specific roles of TRs in liver regeneration after partial hepatectomy (PH).
• To differentiate the contributions of thyroid hormone (T3) levels and TR modulation.

Main Methods:

• Genetic ablation of TRalpha1/TRbeta or TRbeta in mice.
• Pharmacological induction of hypothyroidism.
• Analysis of hepatocyte proliferation, apoptosis, and molecular markers (NOS, ADMA, DDAH-1, FXR, cyclins).

Main Results:

• Mice lacking TRs regenerated liver mass but showed delayed proliferation and increased apoptosis.
• TR deficiency was linked to enhanced nitrosative stress via altered nitric oxide synthase (NOS) activity.
• Changes in asymmetric dimethylarginine (ADMA) and dimethylarginineaminohydrolase-1 (DDAH-1) activity were observed, paralleling FXR activity.

Conclusions:

• TRs are not essential for liver regeneration but TRbeta significantly influences the rate of hepatocyte proliferation and liver mass restoration.
• TRbeta deficiency leads to delayed regeneration and apoptosis, which can be mitigated by NOS inhibitors.
• TRbeta plays a crucial role in ensuring rapid hepatocyte proliferation and survival during liver regeneration.