# Nonerythroid Hemoglobin Present in Porcine Testes

## TL;DR

The study finds hemoglobin in pig testes, suggesting it may help regulate oxygen for sperm development in low-oxygen environments.

## Contribution

It confirms nonerythroid hemoglobin beta presence in porcine testes and its localization in interstitial cells.

## Key findings

- Hemoglobin beta mRNA and protein are present in porcine testes.
- Localization of hemoglobin beta differs between male and female gonads.
- Expression decreases with age due to changes in testicular composition.

## Abstract

Sperm development occurs in the seminiferous tubules within the testes. Sertoli cells and developing germ cells are dependent on oxygen diffusing from capillaries located within the interstitial tissue and diffusing through the interstitial tissue, followed by diffusion through or around the peritubular myoid cells and through the basement membrane. As a result of this long diffusion path, oxygen concentration within the seminiferous tubules is thought to be very low. The qPCR analysis demonstrated the presence of hemoglobin mRNA, consistent with previous reports of the presence of mRNA in the murine testis by microarray analysis. Immunohistochemical localization of protein in the interstitial compartment distinct from the vascular compartment confirms synthesis in this tissue. Although qPCR expression is lower in adult testis than in juvenile testis, the localization of protein in the interstitial compartment and the reduction in the proportion of interstitium with age may be the actual cause for the age-associated reduction in expression. The localization of the hemoglobin protein in the porcine oocyte and surrounding follicle confirmed a similar pattern to that recently reported for rodent and human follicles, supporting a significant difference in localization in gametes and proximal tissue between female and male gonads. This information on expression and localization provides a foundation for further experiments.

The presence of hemoglobin beta mRNA and protein in the female gonad suggests that hemoglobin beta may be present in the male gonad as well. The frequent occurrence of hemoglobin beta in nonerythroid tissues with hypoxic environments further underscores a potential role for hemoglobin beta in the testis to facilitate the regulation of oxygen availability for the developing germ cells and Sertoli cells since they are separated from the blood supply by multiple tissues. The presence of mRNA and protein were evaluated by qPCR and immunohistochemistry, respectively. The mRNA and protein for hemoglobin were detected in juvenile and postpuberal porcine testes. The most intense immunolabelling for the protein was present in testicular interstitial cells, in contrast to previously reported ovarian labelling in close proximity to the gamete and observed in porcine ovaries in the current study. The observed decrease in mRNA expression of hemoglobin beta with age is probably due to the change in testicular composition (increase in seminiferous tubule compartment) with age. The localization of hemoglobin beta in the testis will contribute to future understanding of its potential function in facilitating oxygen availability to seminiferous tubules or reducing oxidative damage.