Transplantation of Microglia in the Area of Spinal Cord Injury in an Acute Period Increases Tissue Sparing, but Not Functional Recovery

Abstract

Microglial cells are known as important mediators of inflammation and immune response in the central nervous system (CNS). However, a neuroprotective role of these cells in post-traumatic processes should not be overlooked. Microglial cells are the first to respond to CNS injury and are further involved in all critical events of pathogenesis. When activated microglia clear the cellular debris and release anti- and proinflammatory cytokines and chemokines, nitric oxide, neurotrophins, and antioxidants capable of producing both neurotoxic and neuroprotective effects. The aim of this study was to determine to what extent the phagocytic activity of microglia in an acute period of spinal cord injury (SCI) in rats can effect the post-traumatic processes. For this purpose we implanted genetically modified Ad5-EGFP or Ad5-GDNF microglial cells into the area of acute SCI. Our experiments demonstrate that the area of intact tissue was lower in the group transplanted with Ad5-GDNF-transduced microglial cells with reduced phagocytic activity than that in the group of animals transplanted with Ad5-EGFP-transduced microglia cells which did not affect the cell activity. At the same time, there was no significant difference in the functional recovery index between these groups. Thus, the increased number of microglia cells with good phagocytic activity in the area of acute SCI may contribute to the improved nervous tissue integrity without a significant effect on the functional recovery within 30 days after injury.

Keywords: adenoviral vector; egfp; gdnf; microglia; spinal cord injury.

FIGURE 1

Analysis of

FIGURE 2

Analysis of the expression of Iba1 and Irf5 mRNA in vitro and in vivo in the area of SCI. Irf5 (A) and Iba1 (B) mRNA expression in vitro on cultivation Days 0, 1, 7, 14. Irf5 and Iba1 mRNA expression of 0 day group was considered 100%. Differences were statistically significant between all time intervals (P < 0.05). Iba1 (C) and irf5 (D) mRNA expression in vivo on day 30 after SCI and cell transplantation. The Iba1 and irf5 mRNA expression levels in Intact controls were considered 100% (C,D). ^∗P < 0.05, one-way ANOVA followed by a Tukey’s post hoc test.

FIGURE 3

Assessment of microglial cells in the area of SCI. The total intensity of Iba1 labeling 5 mm rostrally (A) and caudally (B) from the injury epicenter. ^∗P < 0.05, one-way ANOVA followed by a Tukey’s post hoc test. Assessment of microglial cells with Iba1 5 mm rostrally from the injury epicenter within the CST, VF and VH in the experimental groups (C).

FIGURE 4

Tissue analysis in experimental groups. An area of the intact tissue (A–C) and a total area of abnormal cavities (D–F) 5 mm rostrally and caudally from the injury epicenter on Day 30 after SCI and microglia transplantation. ^∗P < 0.05, one-way ANOVA followed by a Tukey’s post hoc test. Cross sections of the injured spinal cord on Day 30 after SCI in experimental groups (bottom panel). Azur-eosin staining.

FIGURE 5

Assessment of astrocytes in the area of SCI. The total intensity of GFAP labeling 5 mm rostrally (A) and caudally (B) from the injury epicenter. ^∗P < 0.05, one-way ANOVA followed by a Tukey’s post hoc test. Assessment of astrocytes with GFAP 5 mm rostrally from the injury epicenter within the CST and VH in the experimental groups (C).

FIGURE 6

Post-SCI behavioral studies in experimental groups. Assessment of locomotor activity using the BBB rating scale from 7 to 30 days after injury. ^∗P < 0.05, one-way ANOVA followed by a Tukey’s post hoc test.