100 Section - Downregulation of PDCD4 contributes to microglial efferocytosis and neurological function recovery via the JAK2-STAT3-MERTK/AXL axis following intracerebral hemorrhage

Microglial efferocytosis plays a vital role in mitigating neuroinflammatory and neurological recovery processes, but its underlying mechanism remains poorly understood in intracerebral hemorrhage (ICH). Recent research has also revealed that programmed cell death factor 4 (PDCD4) significantly regulates neuroinflammatory responses. However, the specific molecular mechanisms of how PDCD4 influences neurological recovery by regulating microglial efferocytosis in the ICH remain to be elucidated.

Design:

A mouse model of ICH was established using collagenase. Targeted in vivo injection of PDCD4 knockdown adenovirus was administered to ICH model mice, while PDCD4 knockout (KO) mice were utilized as post-ICH validation models. Neurological behavioral functions were assessed using the corner test, forelimb placement test, and Morris water maze. PDCD4 expression and localization in mouse brain tissue, along with microglial efferocytic function, were determined by Western blot analysis, immunofluorescence assays, and FJC staining. An in vitro model was established using oxyhemoglobin, and efferocytosis-related protein expression was quantified by Western blot analysis. Apoptotic neurons labeled with propidium iodide were co-cultured with microglia, while neuronal apoptosis under conditioned medium treatment was evaluated by TUNEL staining.

Results:

PDCD4 expression is upregulated and localized to microglia following ICH. In vivo studies demonstrated that PDCD4 knockdown or knockout significantly improved neurological recovery, enhanced AXL and MERTK expression, and promoted microglial efferocytosis in ICH mice. In vitro experiments confirmed that PDCD4 knockdown upregulated efferocytosis-related molecules AXL and Mertk while enhancing microglial phagocytosis of apoptotic neurons. Mechanistically, PDCD4 interacts with STAT3, an interaction that was amplified following ICH. PDCD4 knockdown facilitated JAK2-mediated STAT3 phosphorylation and nuclear translocation, thereby activating Mertk and Axl transcription. Concurrently, PDCD4 knockdown reduced pro-inflammatory factor IL-6 expression, elevated anti-inflammatory factor IL-10 levels, and attenuated conditioned medium-induced neuronal apoptosis.

Conclusion:

PDCD4 downregulation facilitates microglial efferocytosis following ICH through activation of the JAK2-STAT3-Mertk/Axl axis, positioning PDCD4 as a potential therapeutic target for ICH.