The effect of ubiquitin on immune response after controlled cortical impact injury

Previously, we reported that exogenous ubiquitin reduces cortical contusion volume and tends to reduce brain water content after controlled cortical impact injury Controlled Cortical Impact Injury (CCII) in rats. The mechanisms how exogenous ubiquitin exerts these effects remain unclear. Some studies revealed ubiquitin's immune modulatory abilities; therefore, we hypothesized that ubiquitin influences the local innate inflammatory response after CCII.

Sprague-Dawley rats were exposed to CCII and randomized to either 1.5 mg/kg ubiquitin or 0.9% NaCl intravenously within 5 minutes after CCII. Immune cells were immunohistochemically stained with OX-42, myeloperoxidase (MPO), HIS48, ED1, and glial fibrillary acidic protein (GFAP). Apoptosis was analyzed by using terminal desoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL). Levels of interleukin (IL)-1β, IL-6, IL-10, tumor necrosis factor (TNF)-α, and IL-1 receptor antagonist (IL-1ra) were quantified using real-time reverse-transcriptase polymerase chain reaction (rt-PCR).

ED1-positive cells were significantly increased in the pericontusional cortex after ubiquitin treatment at day 7 (823±182 cells/mm² vs. 550±246 cells/mm²; p=0.04). IL-10 expression after 3 days was significantly lower in the verum group (1.065¹⁰⁻⁵±0.6093¹⁰⁻⁵ vs. 2.266¹⁰⁻⁵±1.244¹⁰⁻⁵ relative messenger RNA expression; p=0.04) and TNF-α-levels tended to be higher in the verum group (22.01¹⁰⁻⁵±10.87¹⁰⁻⁵ vs. 9.34¹⁰⁻⁵±4.44¹⁰⁻⁵ relative messenger RNA; p=0.096). Quantification of apoptotic cells did not differ between the groups.

Exogenous ubiquitin modulates the immune response by influencing the infiltration of macrophages or activated microglia and the expression of IL-10 and possibly TNF-α after CCII. The effects of these changes in immune response on posttraumatic neurodegeneration still need to be clarified.