PITX2 AND PITX1 regulate thyrotroph function and response to hypothyroidism

Area of Science:

• Endocrinology
• Molecular Biology
• Developmental Biology

Background:

• Pitx2 is a homeodomain transcription factor essential for pituitary and organ development.
• Pitx2 plays a dose-dependent role, with null mutations causing severe pituitary hypoplasia.
• Pitx2 is expressed in the fetal pituitary and adult thyrotrophs and gonadotrophs.

Purpose of the Study:

• To investigate the specific role of Pitx2 in thyrotroph function.
• To develop a thyrotroph-specific Cre transgenic mouse model for gene ablation.
• To elucidate the interplay between Pitx2 and Pitx1 in thyroid hormone regulation.

Main Methods:

• Generation of thyrotroph-specific Pitx2-deficient mice (Pitx2(flox/-);Tg(Tshb-cre)).
• Utilized a novel Tg(Tshb-Cre) bacterial artificial chromosome.
• Confirmed Pitx2 deletion via double immunohistochemistry.
• Assessed thyroid gland size, circulating hormone levels (T4, TSH), and Pitx1 transcript levels.
• Induced hypothyroidism using a low-iodine diet and propylthiouracil.

Main Results:

• Thyrotroph-specific Pitx2 deficiency resulted in smaller thyroid glands but normal circulating T4 and TSH levels.
• Pituitary Pitx1 transcript levels were significantly increased in Pitx2-deficient mice, suggesting compensation.
• Pitx2-deficient mice exhibited a blunted TSH response to induced hypothyroidism.
• Pitx1 upregulation in response to hypothyroidism was abolished in Pitx2-deficient mice.

Conclusions:

• PITX2 and PITX1 have overlapping functions in thyrotroph biology.
• PITX2 is involved in the thyrotroph response to hypothyroidism.
• The developed Tg(Tshb-Cre) mouse line is a valuable tool for studying gene function in thyrotrophs.