Protection of erythropoietin on experimental spinal cord injury by reducing the expression of thrombospondin-1 and transforming growth factor-beta

Abstract

Background: Erythropoietin (EPO) functions as a tissue-protective cytokine in addition to its crucial hormonal role in red cell production and neuron protection. This study aimed to determine the neuron protective effect of erythropoietin on experimental rats enduring spinal cord injury (SCI) by assessing thrombospondin-1 (TSP-1) level and transforming growth factor-beta (TGF-beta) in the development of a rat model of SCI.

Methods: Sixty Sprague-Dawley rats were randomly assigned to three groups: sham operation control group, SCI group and EPO treatment group. By using a weight-drop contusion SCI model, the rats in the SCI group and EPO treatment group were sacrificed at 24 hours and 7 days subsequently. The Basso, Beattie, and Bresnahan (BBB) scores were examined for locomotor function. Pathological changes were observed after HE staining. The expressions of thrombospondin-2 (TSP-1) and TGF-beta were determined by immunohistochemical staining and Western blotting.

Results: Slighter locomotor dysfunction was discovered and it was recovered abruptly as higher BBB scores were found in the EPO treatment group than in the SCI group (P < 0.01). Pathologically, progressive disruption of the dorsal white matter and regeneration of a few neurons were also observed in SCI rats. TSP-1 and TGF-beta expression increased at 24 hours and 7 days after SCI in the injured segment, and it was higher in the SCI group than in the EPO treatment group. Spinal cord samples from the animals demonstrated a TSP-1 optical density of 112.2 +/- 6.8 and TSP-1 positive cells of 5.7 +/- 1.3 respectively. After injury, the TSP-1 optical density and cell number increased to 287.2 +/- 14.3/mm(2) and 23.2 +/- 2.6/mm(2) at 24 hours and to 232.1 +/- 13.2/mm(2) and 15.2 +/- 2.3/mm(2) at 7 days respectively. When EPO treated rats compared with the SCI rats, the TSP-1 optical density and cell number decreased to 213.1 +/- 11.6/mm(2) and 11.9 +/- 1.6/mm(2) at 24 hours and to 189.9 +/- 10.5/mm(2) and 9.3 +/- 1.5/mm(2) at 7 days, respectively (P < 0.01). In the SCI rats, the TGF-beta optical density and positive neuron number were 291.4 +/- 15.2/mm(2) and 28.8 +/- 4.9/mm(2) at 24 hours and 259.1 +/- 12.3/mm(2) and 23.9 +/- 4.1/mm(2) at 7 days respectively. They decreased in the EPO treated rats to 222.8 +/- 11.9/mm(2) and 13.7 +/- 2.1/mm(2) at 24 hours and to 196.5 +/- 9.7/mm(2) and 8.7 +/- 2.2/mm(2) at 7 days (P < 0.01).

Conclusions: Increased expression of TSP-1 and TGF-beta can be found in the injured segment of the spinal cord at 24 hours and 7 days after injury. EPO treatment can effectively prevent pathological alterations from severe spinal cord injury by reduced expression of TSP-1 and TGF-beta.