Age and neuroinflammation are important components of the mechanism of cognitive and neurobehavioral deficits in sickle cell disease

Objectives: Cognitive and neurobehavioral abnormalities are the most common and complex complications of sickle cell disease (SCD). Known risk factors influencing abnormalities are stroke and silent cerebral infarcts, but a majority of cases do not have overt cerebral injury and the underlying mechanism is not well understood. This study aims to determine whether sickle cell mice could recapitulate features of cognitive and neurobehavioral impairment observed in sickle cell patients as well as to determine the underlying cellular mechanism of these SCD complications. Methods: Using a longitudinal cross-sectional study design, we evaluated cognition and neurobehavioral deficits as an outcome. Six as well as 13 months old male Townes humanized sickle cell (SS) and matched control (AA) mice were tested. The combination of novel object recognition and fear conditioning tests was employed to measure anxiety/depression, learning and memory. Immunohistochemistry was performed to quantify bone marrow-derived microglia (CD45+) and activated microglia (Iba1+) in the dentate and peri-dentate gyrus to determine if these factors were potential pathogenic mechanisms associated with cognitive and neurobehavioral abnormalities. We evaluated neurogenesis by measuring 5′Bromodeoxyuridine (BrdU) and doublecortin (DCX) and phenotyped proliferating cells via quantification of glial fibrillary acid protein (GFAP+), neuronal nuclei (NeuN+), CD45+ and Iba1+. In addition, Golgi-Cox staining was used to assess neuroplasticity via measurement of dendritic spine density and morphology, as well as dendrite arbors. Results: Compared to matched AA, 13 months old SS mice showed significant evidence of anxiety/depression by the shorter distance traveled as well as thigmotaxis. Additionally, SS mice were significantly less likely to recognize the novel object as well as have a reduced preference for the novel object. There were no significant differences between 6 months old SS and AA. But the difference reappeared after the same mice were aged to 13 months. Aged mice exhibited more anxiety/depression behaviors and thigmotaxis and were less likely to recognize or show a lower percent preference for the novel object compared to aged control (AA) mice. Immunohistochemistry analysis shows that sickle cell (SS) mice had significantly more CD45+ and Iba1+ activated microglia cells in the dentate and peri-dentate gyrus area compared to AA mice. SS mice also had a significantly lower dendritic spine density compared with controls. Treatment of aged SS mice with minocycline resulted in significant improvement of cognitive and neurobehavioral function compared to matched vehicle-treated SS mice. Also immunohistochemical and histological analysis showed that treated SS mice had significantly fewer CD45+ cells and activated microglia in the dentate and peri-dentate gyrus area. Furthermore, there was significant improvement in dendritic spine and dendrite arbor density as well as spine maturation in treated sickle cell mice compared with vehicle-treated sickle cell mice. Conclusion: Taken together these results indicate that age, neuro-inflammation and neuroplasticity, specifically, spine maturation and density, are possible mechanisms underlying cognition deficits in sickle cell disease. These could also be targeted as a potential approach for prevention and or treatment of cognitive and neurobehavioral deficits in SCD.