Severity- and Time-Dependent Activation of Microglia in Spinal Cord Injury

Microglia Promote Lymphangiogenesis Around the Spinal Cord Through VEGF-C/VEGFR3-Dependent Autophagy and Polarization After Acute Spinal Cord Injury

Reducing secondary injury is a key focus in the field of spinal cord injury (SCI). Recent studies have revealed the role of lymphangiogenesis in reducing secondary damage to central nerve. However, the mechanism of lymphangiogenesis is not yet clear. Macrophages have been shown to play an important role in peripheral tissue lymphangiogenesis. Microglia is believed to play a role similar to macrophages in the central nervous system (CNS); we hypothesized that there was a close relationship between microglia and central nerve system lymphangiogenesis. Herein, we used an in vivo model of SCI to explored the relationship between microglia and spinal cord lymphangiogenesis and further investigated the polarization of microglia and its role in promoting spinal cord lymphangiogenesis by a series of in vitro experiments. The current study elucidated for the first time the relationship between microglia and lymphangiogenesis around the spinal cord after SCI. Classical activated (M1) microglia can promote lymphangiogenesis by secreting VEGF-C which further increases polarization and secretion of lymphatic growth factor by activating VEGFR3. The VEGF-C/VEGFR3 pathway activation downregulates microglia autophagy, thereby regulating the microglia phenotype. These results indicate that M1 microglia promote lymphangiogenesis after SCI, and activated VEGF-C/VEGFR3 signaling promotes M1 microglia polarization by inhibiting autophagy, thereby facilitates lymphangiogenesis.

Fascin-1 limits myosin activity in microglia to control mechanical characterization of the injured spinal cord

BACKGROUND

Mechanical softening of the glial scar region regulates axonal regeneration to impede neurological recovery in central nervous system (CNS) injury. Microglia, a crucial cellular component of the glial scar, facilitate neuronal survival and neurological recovery after spinal cord injury (SCI). However, the critical mechanical characterization of injured spinal cord that harmonizes neuroprotective function of microglia remains poorly understood.

METHODS

Spinal cord tissue stiffness was assessed using atomic force microscopy (AFM) in a mouse model of crush injury. Pharmacological depletion of microglia using PLX5622 was used to explore the effect of microglia on mechanical characterization. Conditional knockout of Fascin-1 in microglia (Fascin-1 CKO) alone or in combination with inhibition of myosin activity was performed to delve into relevant mechanisms of microglia regulating mechanical signal. Immunofluorescence staining was performed to evaluate the related protein levels, inflammatory cells, and neuron survival after SCI. The Basso mouse scale score was calculated to assess functional recovery.

RESULTS

Spinal cord tissue significantly softens after SCI. Microglia depletion or Fascin-1 knockout in microglia limits tissue softening and alters mechanical characterization, which leads to increased tissue pathology and impaired functional recovery. Mechanistically, Fascin-1 inhibits myosin activation to promote microglial migration and control mechanical characterization after SCI.

CONCLUSIONS

We reveal that Fascin-1 limits myosin activity to regulate mechanical characterization after SCI, and this mechanical signal should be considered in future approaches for the treatment of CNS diseases.

Current methods for the microglia isolation: Overview and comparative analysis of approaches

Microglia represent a distinct population of neuroglia, constituting ~ 10% of all CNS cells and exhibit high plasticity. Proper functioning of microglia is critical in the event of CNS damage due to the rapid modulation of their functions. Microglia are not only the first stage of immune defense against injury and infection, contributing to both the innate and adaptive local immune response, but also play a vital role in maintaining homeostasis of the brain and spinal cord. For this reason, microglia deserve special attention in the study of neuropathological responses. Studying microglia behavior in various in vivo models of neuropathologies is certainly a priority, as it allows us to evaluate the behavior in the context of the changing microenvironment of nervous tissue. However, sometimes there are some technological problems that hinder the identification of the features of intercellular interactions, ensured cooperation between microglia and other cell types. In this regard, the use of in vitro models remains relevant today, contributing to a more in-depth understanding of the mechanisms of microglial involvement in neuropathology. The methods considered in this review for obtaining an isolated culture of microglia, along with their advantages and disadvantages, can help researchers in selecting the appropriate source and method for obtaining these cells, thereby opening up opportunities for gaining new neurobiological knowledge.