Authors :
Presenting Author: Amy Brewster, PhD – Southern Methodist University
Sahar Khan, BS – Southern Methodist University; Shikha Kumari, PhD – Postdoctoral Associate, Biological Sciences, Southern Methodist University; Yibo Li, MS – Research Assistant, Biological Sciences, Southern Methodist University; Phuoc Nguyen, BS – Southern Methodist University
Rationale:
A prominent pathological feature of epilepsy is activation of microglia, the brain’s immune cells and professional phagocytes. Although it is known that microglia mediate inflammatory responses during and after seizures, considerably less is known about the contribution of microglial phagocytic properties to the neuropathology and pathophysiology of epilepsy. Recently, we found altered levels of phagocytosis-related signaling molecules in brain biopsies from patients with drug-resistant epilepsy, that included increases in complement molecules C3b and C1q, and decreases in the levels of the microglial phagocytic receptor Triggering Receptor Expressed On Myeloid Cells 2 (Trem2). Trem2 signaling contributes to microglial survival and proliferation as well as to phagocytosis and the control of inflammatory signals. Interestingly, loss of function mutations are seen in Nasu-Hakola syndrome, a disease associated with neurological decline and seizures. This suggests the possibility that downregulation of Trem2 may impact seizure severity. However, little is known on the status of Trem2 signaling in epilepsy. Therefore, here determined Trem2 protein levels along with the associated downstream signaling molecules in brain tissues from human drug-resistant epilepsy cases.
Methods:
Temporal cortical tissues surgically resected from patients with refractory epilepsy were collected
with patients’ informed consent under approved IRB protocols (n=42;
males, n=21; females, n=21).
Tissues were processed for western blots and Enzyme Linked Immunosorbent Assay (ELISA) to measure
protein levels of Trem2, soluble(s) Trem2, and associated downstream effectors including Dap12, AKT/mTOR, ERK, SYK, GSK3β (phosphorylated and total). In parallel we assessed levels of IBA1, a marker for microglia, along with multiple cytokines and complement proteins. Results:
We found sex differences in the levels of Trem2, sTrem2, Dap12, SYK, mTOR marker P-S6 (S235/236), and the cytokines IL6 and IL8, and complement C3. Specifically, we found that males had lower levels of Trem2 (p=0.003), Dap12 (trend, p = 0.09), and SYK (trend, p = 0.06) and higher levels sTrem2 (p = 0.003), P-S6 (S235/236) (p = 0.05), IL6 (p = 0.05), and IL8 (p = 0.02) compared to females. Levels of AKT, ERK, GSK3β, PS6 (S240/244), TNFβ, IFN-γ, IL4, IL10, and IBA1 were not different between males and females (p > 0.05).
Conclusions:
To our knowledge, this is the first study showing that activation of immune signaling cascades is different in males and females with human refractory epilepsy. We found that decreases in Trem2 signaling correlated with increases in the inflammatory cytokines IL8 and IL6 as well as to complement C3, suggesting a possible link between these events. While mechanistic studies are needed to understand the impact of Trem2 signaling in the pathology of epilepsy, our findings suggest that sex differences in immune signaling may need to be taken into consideration for therapeutic interventions.
Funding:
NS096234 (ALB)
Children’s Brain Diseases Foundation (ALB)
SMU Biological Sciences Startup funds