An Image-Based miRNA Screen Identifies miRNA-135s As Regulators of CNS Axon Growth and Regeneration by Targeting Krüppel-like Factor 4

Abstract

During embryonic development, axons extend over long distances to establish functional connections. In contrast, axon regeneration in the adult mammalian CNS is limited in part by a reduced intrinsic capacity for axon growth. Therefore, insight into the intrinsic control of axon growth may provide new avenues for enhancing CNS regeneration. Here, we performed one of the first miRNome-wide functional miRNA screens to identify miRNAs with robust effects on axon growth. High-content screening identified miR-135a and miR-135b as potent stimulators of axon growth and cortical neuron migration and in male and female mice. Intriguingly, both of these developmental effects of miR-135s relied in part on silencing of Krüppel-like factor 4 (KLF4), a well known intrinsic inhibitor of axon growth and regeneration. These results prompted us to test the effect of miR-135s on axon regeneration after injury. Our results show that intravitreal application of miR-135s facilitates retinal ganglion cell (RGC) axon regeneration after optic nerve injury in adult mice in part by repressing KLF4. In contrast, depletion of miR-135s further reduced RGC axon regeneration. Together, these data identify a novel neuronal role for miR-135s and the miR-135-KLF4 pathway and highlight the potential of miRNAs as tools for enhancing CNS axon regeneration. Axon regeneration in the adult mammalian CNS is limited in part by a reduced intrinsic capacity for axon growth. Therefore, insight into the intrinsic control of axon growth may provide new avenues for enhancing regeneration. By performing an miRNome-wide functional screen, our studies identify miR-135s as stimulators of axon growth and neuron migration and show that intravitreal application of these miRNAs facilitates CNS axon regeneration after nerve injury in adult mice. Intriguingly, these developmental and regeneration-promoting effects rely in part on silencing of Krüppel-like factor 4 (KLF4), a well known intrinsic inhibitor of axon regeneration. Our data identify a novel neuronal role for the miR-135-KLF4 pathway and support the idea that miRNAs can be used for enhancing CNS axon regeneration.

MiR-135-5p-p62 Axis Regulates Autophagic Flux, Tumorigenic Potential, and Cellular Interactions Mediated by Extracellular Vesicles During Allergic Inflammation

“…Intravitreal application of miR-135 facilitates retinal ganglion cell (RGC) axon regeneration after optic nerve injury in adult mice in part by repressing KLF4 (44). Lack of Kruppel-like factor 4 (KLF4) expression in monocytes and lung epithelial cells decreases Th2 cytokines in mice and airway hyper responsiveness (AHR) (45).…”

Epilepsy miRNA Profile Depends on the Age of Onset in Humans and Rats

“…Based on the literature, this miRNA mediates the expression of various proteins included in brain function and neuron development, e.g., serotonin receptor and transporter ( Artigas et al, 2018 ) or complexin 1/2 in the amygdala ( Mannironi et al, 2018 ). It also regulates developmental axon growth and branching, cortical neuronal migration, or regeneration of retinal ganglion cell axons ( van Battum et al, 2018 ). Besides, recent findings revealed that miR-135a-5p affects spontaneous recurrent seizures in the TLE model ( Vangoor et al, 2019 ), which confirms our finding.…”

Construction and reconstruction of brain circuits: normal and pathological axon guidance

“…Recent findings indicate that micro RNAs 135a and 135b (miRNA135s) could regulate KLF4 expression during axon development. Intravitreal administration of miRNA135 induced axon regeneration following ON injury, in part by suppressing KLF4 expression in RGCs (van Battum et al ). SOX11, on the other hand, plays a dual role.…”