Browsing by Author "Mills, Jatia"
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- Cross-Talk and Subset Control of Microglia and Associated Myeloid Cells in Neurological DisordersMills, Jatia; Ladner, Liliana; Soliman, Eman; Leonard, John; Morton, Paul D.; Theus, Michelle H. (MDPI, 2022-10-25)Neurological disorders are highly prevalent and often lead to chronic debilitating disease. Neuroinflammation is a major driver across the spectrum of disorders, and microglia are key mediators of this response, gaining wide acceptance as a druggable cell target. Moreover, clinical providers have limited ability to objectively quantify patient-specific changes in microglia status, which can be a predictor of illness and recovery. This necessitates the development of diagnostic biomarkers and imaging techniques to monitor microglia-mediated neuroinflammation in coordination with neurological outcomes. New insights into the polarization status of microglia have shed light on the regulation of disease progression and helped identify a modifiable target for therapeutics. Thus, the detection and monitoring of microglia activation through the inclusion of diagnostic biomarkers and imaging techniques will provide clinical tools to aid our understanding of the neurologic sequelae and improve long-term clinical care for patients. Recent achievements demonstrated by pre-clinical studies, using novel depletion and cell-targeted approaches as well as single-cell RNAseq, underscore the mechanistic players that coordinate microglial activation status and offer a future avenue for therapeutic intervention.
- Efferocytosis is restricted by axon guidance molecule EphA4 via ERK/Stat6/MERTK signaling following brain injurySoliman, Eman; Leonard, John; Basso, Erwin K. G.; Gershenson, Ilana; Ju, Jing; Mills, Jatia; de Jager, Caroline; Kaloss, Alexandra M.; Elhassanny, Mohamed; Pereira, Daniela; Chen, Michael; Wang, Xia; Theus, Michelle H. (2023-11-09)Background Efferocytosis is a process that removes apoptotic cells and cellular debris. Clearance of these cells alleviates neuroinflammation, prevents the release of inflammatory molecules, and promotes the production of anti-inflammatory cytokines to help maintain tissue homeostasis. The underlying mechanisms by which this occurs in the brain after injury remain ill-defined. Methods We used GFP bone marrow chimeric knockout (KO) mice to demonstrate that the axon guidance molecule EphA4 receptor tyrosine kinase is involved in suppressing MERTK in the brain to restrict efferocytosis of resident microglia and peripheral-derived monocyte/macrophages. Results Single-cell RNAseq identified MERTK expression, the primary receptor involved in efferocytosis, on monocytes, microglia, and a subset of astrocytes in the damaged cortex following brain injury. Loss of EphA4 on infiltrating GFP-expressing immune cells improved functional outcome concomitant with enhanced efferocytosis and overall protein expression of p-MERTK, p-ERK, and p-Stat6. The percentage of GFP+ monocyte/macrophages and resident microglia engulfing NeuN+ or TUNEL+ cells was significantly higher in KO chimeric mice. Importantly, mRNA expression of Mertk and its cognate ligand Gas6 was significantly elevated in these mice compared to the wild-type. Analysis of cell-specific expression showed that p-ERK and p-Stat6 co-localized with MERTK-expressing GFP + cells in the peri-lesional area of the cortex following brain injury. Using an in vitro efferocytosis assay, co-culturing pHrodo-labeled apoptotic Jurkat cells and bone marrow (BM)-derived macrophages, we demonstrate that efferocytosis efficiency and mRNA expression of Mertk and Gas6 was enhanced in the absence of EphA4. Selective inhibitors of ERK and Stat6 attenuated this effect, confirming that EphA4 suppresses monocyte/macrophage efferocytosis via inhibition of the ERK/Stat6 pathway. Conclusions Our findings implicate the ERK/Stat6/MERTK axis as a novel regulator of apoptotic debris clearance in brain injury that is restricted by peripheral myeloid-derived EphA4 to prevent the resolution of inflammation.
- Influence of Peripheral Immune-Derived EphA4 on Microglial Dynamics Following Traumatic Brain InjuryMills, Jatia (Virginia Tech, 2024-07-30)Traumatic brain injury (TBI) elicits an immediate neuroinflammatory response that involves resident glia and infiltrating peripheral immune cells that coordinate tissue damage and functional deficits. The activation of resident microglial has been associated with a change in their morphology from a branched-like ramified cell to an ameboid state. This activation is thought to initiate a pro-inflammatory response leading to the release of neurotoxic, immune chemoattractant, and antigen-presenting signals. Subsequently, peripheral-derived immune cells (PICs), such as neutrophils and monocytes, travel to the site of injury and help coordinate this response. However, little is known regarding whether PICs influence the progressive activation state of microglia in the acute and chronic phases of injury. Overactivation of microglia can lead to neuroinflammation-mediated tissue damage and death or dysfunction of healthy neurons. Therefore, understanding how microenvironmental cues may regulate the microglial response may aid in strategies to retool their activation state in the brain. EphA4 receptor tyrosine kinase has been identified as a potential cell-to-cell contact protein on PICs that could be involved in the inflammatory changes following TBI. While microglial activation changes have been described in TBI models, the mechanistic role of infiltrating peripheral-derived immune cell (PIC) recruitment on microglial fate and function is not well understood. The purpose of my project is to gain a better understating of the temporospatial influence that EphA4-expressing PICs, specifically monocyte/macrophages, have on microglial proliferation, survival, activation phenotype, and debris clean-up using bone marrow GFP chimeric mice and the cortical contusion injury TBI model.