Genetic Deletion ofCdc42Reveals a Crucial Role for Astrocyte Recruitment to the Injury SiteIn VitroandIn Vivo

Abstract

It is generally suggested that astrocytes play important restorative functions after brain injury, yet little is known regarding their recruitment to sites of injury, despite numerous in vitro experiments investigating astrocyte polarity. Here, we genetically manipulated one of the proposed key signals, the small RhoGTPase Cdc42, selectively in mouse astrocytes in vitro and in vivo. We used an in vitro scratch assay as a minimal wounding model and found that astrocytes lacking Cdc42 (Cdc42⌬) were still able to form protrusions, although in a nonoriented way. Consequently, they failed to migrate in a directed manner toward the scratch. When animals were injured in vivo through a stab wound, Cdc42⌬ astrocytes developed protrusions properly oriented toward the lesion, but the number of astrocytes recruited to the lesion site was significantly reduced. Surprisingly, however, lesions in Cdc42⌬ animals, harboring fewer astrocytes contained significantly higher numbers of microglial cells than controls. These data suggest that impaired recruitment of astrocytes to sites of injury has a profound and unexpected effect on microglia recruitment.

Astrocyte Reactivity and Reactive Astrogliosis: Costs and Benefits

“…Notably, these mice showed also a more pronounced functional impairment (95,163,256). Similarly, selective ablation of the small RhoGTPase Cdc42 in astrocytes impaired their recruitment to the stab wound lesion and was accompanied by higher density of microglia in the lesion (192). Attenuation of reactive astrogliosis by constitutive GFAP and vimentin ablation was associated with increased numbers of microglial cells in plaque vicinity in a mouse model of AD (125) (FIGURE 9C).…”

“…EGFR ligands stimulate the secretion of chondroitin sulfate proteoglycans, and inhibition of EGFR signaling enhances axonal regeneration and improves functional recovery after CNS injury (69,123,218). Astrocyte polarity and directional migration seem to play a crucial role in astrocyte ability to react to injury: astrocytes depleted of the small RhoGTPase Cdc42, a key regulator of cell polarization, show impaired recruitment to the stab wound lesion despite their upregulation of GFAP and hypertrophic response (192). On a morphological level, reactive astrogliosis ranges from subtle to moderate to very prominent, with the prominent one being often accompanied by glial scarring, a phenomenon known by generations of neuropathologists (221).…”

Phenotypic Assays to Identify Agents That Induce Reactive Gliosis: A Counter-Screen to Prioritize Compounds for Preclinical Animal Studies

“…Kinases are attractive drug targets because they are involved in many cellular processes, including neurite outgrowth, axon regeneration, and reactive gliosis. [61][62][63][64] Until recently, there was little information about the ability of various KIs to manipulate axon/neurite growth. 39,40,65 Importantly, there is even less information about how KIs might affect the astroglial reaction to CNS injury.…”

Real-Time PCR and Immunocytochemical Study of Chondroitin Sulfate Proteoglycans after Scratch Wounding in Cultured Astrocytes / PCR I IMUNOCITOHEMIJSKA STUDIJA EKSPRESIJE HONDROITIN-SULFATNIH PROTEOGLIKANA NAKON POVREDE ASTROCITA U KULTURI

“…One of such is a scratchwound assay (SW), first established as a simple, reproducible assay for the analysis of cell migration in vitro (13). The SW model was soon adopted by many to investigate different aspects of astroglial response to mechanical injury (14)(15)(16)(17). As a response to SW injury, the following characteristics of reactive astrocytes have been observed: hyperplasia, enhanced expression of extracellular matrix molecules and elongation of hypertrophic processes (18,19).…”