Gonadotropin-releasing hormone stimulation of annexin A5 expression in the thymus of male rats

Abstract

As gonadotropin-releasing hormone (GnRH) is expressed in the thymus, its direct action on thymic cells, including thymic involution, has been suggested. Annexin A5 (ANXA5), a biomarker of GnRH, was used to determine whether GnRH affects the thymus of male rats. Immunohistochemistry showed positive reactions for ANXA5 in large medullary epithelial cells at 30 days of age, and the expression continued until 180 days of age. Organ culture of thymus pieces was performed to examine the direct action of a GnRH agonist (GnRHa) on the expression of Anxa5 and Gnrh mRNA. Thymus tissues obtained from male rats (40-60 days old) were cut into small pieces (2-3 mm³) and incubated for 3 hr with the GnRHa. The expression levels of Anxa5 and Gnrh mRNA were augmented by the GnRHa. Immunohistochemistry of these tissue fragments showed that ANXA5 expression was enhanced, especially in medullary epithelial cells. These results revealed that GnRH synthesis in the thymus could affect thymic epithelial cells after puberty.

Keywords: annexin A5 (ANXA5); gonadotropin-releasing hormone (GnRH); thymus.

Fig. 1.

Immunohistochemistry of annexin A5 (ANXA5) in rat thymus tissue. The expression of ANXA5 in the thymus of rats aged 0–180 days was examined by immunohistochemistry using an anti-ANXA5 antibody. (A) Thymus tissues showing the cortex and medulla. Intense immunoreactions in the cortex and medulla are indicated by the red and black arrows, respectively. (B) Enlarged medulla. Blue arrowheads indicate epithelial cells stained for ANXA5. Blue arrowheads indicate Hassal corpuscle-like structures.

Fig. 2.

Changes in the thymus weight. The body and thymus weights of male rats were measured at 0, 30, 60, and 180 days of age. The (A) body weight, and (B) thymus weight. Different letters indicate a statistical difference at P<0.05.

Fig. 3.

Changes in thymic Anxa5 and Gnrh mRNA after gonadotropin releasing hormone agonist (GnRHa) treatment in the organ culture of thymus tissue. Thymus tissues from male rats (40–60 days old) were cut into 2–3 mm³ blocks and incubated with 10⁻⁹ M GnRHa for 3 hr at 37°C with 5% CO₂ and 40% O₂. The expression levels of thymic (A) Anxa5 and (B) Gnrh mRNA were measured by qRT-PCR. Asterisks indicate a significant difference (P<0.05).

Fig. 4.

Immunohistochemistry of annexin A5 (ANXA5) in cultured thymus tissue. (A and C) Control. (B and D) gonadotropin releasing hormone agonist (GnRHa)-treated tissues. Black arrowheads indicate intense staining.