Transferrin receptor expression in serum exosomes as a marker of regenerative anaemia in the horse.

Abstract

REASONS FOR PERFORMING STUDY: Evaluation of erythrocyte regeneration in horses is challenging, as they do not release reticulocytes into the peripheral blood. This study investigated transferrin receptor 1 (TfR1) expression in exosomes as a noninvasive method of characterising the regenerative response in anaemic horses. OBJECTIVES: To quantify TfR1 in ultraprecipitate of serum in horses before and after phlebotomy-induced anaemia, and to identify exosomes as the source of TfR1. The hypothesis was that serum exosomal TfR1 expression would increase during a regenerative response. STUDY DESIGN: Experimental model of anaemia. METHODS: Six horses were phlebotomised to achieve a 25% decrease in packed cell volume. Transferrin receptor 1 quantity in exosomes was determined by western blot and relative densitometry before and after phlebotomy. The size and density of the TfR1-associated particles were confirmed by transmission electron microscopy and density gradient centrifugation, respectively. RESULTS: Regenerative anaemia was confirmed by decreased packed cell volumes and decreased myeloid:erythroid ratios in the bone marrow. In all 6 horses, TfR1 expression increased between Days 7 and 10. Mean TfR1 levels peaked on Day 10 and at 3-fold higher than levels on Day 0. Appropriately sized particles were evident on transmission electron microscopy and sucrose density gradient fractions expected to contain exosomes also contained TfR1. CONCLUSIONS: These data indicate that TfR1 expression in serum exosomes may provide a marker for regeneration in anaemic horses.