Inhibition of miR-155 Limits Neuroinflammation and Improves Functional Recovery After Experimental Traumatic Brain Injury in Mice

Abstract

Micro-RNAs (miRs) are short, noncoding RNAs that negatively regulate gene expression at the post-transcriptional level and have been implicated in the pathophysiology of secondary damage after traumatic brain injury (TBI). Among miRs linked to inflammation, miR-155 has been implicated as a pro-inflammatory factor in a variety of organ systems. We examined the expression profile of miR-155, following experimental TBI (controlled cortical impact) in adult male C57Bl/6 mice, as well as the effects of acute or delayed administration of a miR-155 antagomir on post-traumatic neuroinflammatory responses and neurological recovery. Trauma robustly increased miR-155 expression in the injured cortex over 7 days. Similar TBI-induced miR-155 expression changes were also found in microglia/macrophages isolated from the injured cortex at 7 days post-injury. A miR-155 hairpin inhibitor (antagomir; 0.5 nmol), administered intracerebroventricularly (ICV) immediately after injury, attenuated neuroinflammatory markers at both 1 day and 7 days post-injury and reduced impairments in spatial working memory. Delayed ICV infusion of the miR-155 antagomir (0.5 nmol/day), beginning 24 h post-injury and continuing for 6 days, attenuated neuroinflammatory markers at 7 days post-injury and improved motor, but not cognitive, function through 28 days. The latter treatment limited NADPH oxidase 2 expression changes in microglia/macrophages in the injured cortex and reduced cortical lesion volume. In summary, TBI causes a robust and persistent neuroinflammatory response that is associated with increased miR-155 expression in microglia/macrophages, and miR-155 inhibition reduces post-traumatic neuroinflammatory responses and improves neurological recovery. Thus, miR-155 may be a therapeutic target for TBI-related neuroinflammation.

Microglial depletion with CSF1R inhibitor during chronic phase of experimental traumatic brain injury reduces neurodegeneration and neurological deficits

“…Beam walk: Fine motor coordination was assessed using a beam walk test, as previously described (Kumar et al, 2016b;Henry et al, 2019). Briefly, mice were placed on one end of a wooden beam (5 mm wide and 120 mm in length), and the number of foot faults of the right hind limb were recorded over 50 steps.…”

“…The Y-maze was performed at 70 dpi to test spatial working memory in mice, as previously described (Kumar et al, 2016b;Henry et al, 2019). Briefly, the Ymaze (Stoelting Co., Wood Dale, IL) consisted of three identical arms, each arm 35 cm long, 5 cm wide, and 10 cm high, at an angle of 120° with respect to the other arms.…”

“…Quantification was based on the Cavalieri method using Stereoinvestigator Software (MBF Biosciences, Williston, VT), as previously described (Byrnes et al, 2012;Henry et al, 2019). Briefly, the lesion volume was quantified by outlining the missing tissue on the injured hemisphere using the Cavalieri estimator with a grid spacing of 0.1 mm.…”

“…Immunofluorescence imaging was carried out on 20 µm coronal brain sections at approximately -1.70 mm from bregma. Standard immunostaining techniques were employed, as previously described (Henry et al, 2019). Briefly, 20 µm brain sections were washed three times with 1x PBS, blocked for 1 hour in goat serum containing 0.4% Triton X-100, and incubated overnight at 4°C with a combination of primary antibodies, including mouse anti-gp91 phox (NOX2; 1:1000, BD Biosciences, San Jose, CA), rat anti-CD68 (1:1000, AbD Serotec Inc., Raleigh, NC), rabbit anti-Iba1 (1:1000, Wako Chemicals) and chicken anti-GFAP (1:500, Abcam, Eugene, OR).…”

Silencing MicroRNA-155 Attenuates Kainic Acid-Induced Seizure by Inhibiting Microglia Activation

“…In the central nervous system, miR-155 has been found to be a major regulator of proinflammatory responses in immunity [21-23]. It was highly upregulated during macrophage inflammatory responses and in multiple sclerosis lesions [24, 25].…”