Histochemical examination of blood vessels in murine femora with intermittent PTH administration

Abstract

Objective: To verify the biological effects of parathyroid hormone (PTH) on the blood vessels in the bone, this study aimed to investigate histological alterations in endomucin-positive blood vessels and perivascular cells in murine femora after intermittent PTH administration. For comparison with blood vessels in the bone, we examined the distribution of endomucin-positive blood vessels and surrounding αSMA-immunoreactive perivascular cells in the liver, kidney, and aorta with or without PTH administration.

Methods: Six-week-old male C57BL/6J mice received hPTH [1-34] or vehicle for two weeks. All mice were fixed with a paraformaldehyde solution after euthanasia, and the right femora, kidney, liver, and aorta were extracted for immunohistochemical analysis of endomucin, αSMA, ephrinB2, EphB4, and HIF1α. Light microscopic observations of semi-thin sections and transmission electron microscopic (TEM) observations of ultra-thin sections were performed on the left femora.

Results: After intermittent PTH administration, αSMA-reactive/ephrinB2-positive stromal cells appeared around endomucin-positive/EphB4-immunoreactive blood vessels in the bone. In addition, intense immunoreactivities of EphB4 and HIF1α were seen in vascular endothelial cells after the PTH treatment. Several stromal cells surrounding PTH-treated blood vessels exhibited well-developed rough endoplasmic reticulum under TEM observations. In contrast to bone tissues, αSMA-positive stromal cells did not increase around the endomucin-positive blood vessels in the kidney, liver, or aorta, even after PTH administration.

Conclusion: These findings show that intermittent PTH administration increases αSMA-reactive/ephrinB2-positive perivascular stromal cells in bone tissue but not in the kidney, liver, or aorta, suggesting that PTH preferentially affects blood vessels in the bone.

Keywords: Blood vessels; Endomucin; Parathyroid hormone (PTH); Perivascular stromal cells; αSMA.