The Transcriptional Activator Krüppel-like Factor-6 Is Required for CNS Myelination

Abstract

Growth factors of the gp130 family promote oligodendrocyte differentiation, and viability, and myelination, but their mechanisms of action are incompletely understood. Here, we show that these effects are coordinated, in part, by the transcriptional activator Krüppel-like factor-6 (Klf6). Klf6 is rapidly induced in oligodendrocyte progenitors (OLP) by gp130 factors, and promotes differentiation. Conversely, in mice with lineage-selective Klf6 inactivation, OLP undergo maturation arrest followed by apoptosis, and CNS myelination fails. Overlapping transcriptional and chromatin occupancy analyses place Klf6 at the nexus of a novel gp130-Klf-importin axis, which promotes differentiation and viability in part via control of nuclear trafficking. Klf6 acts as a gp130-sensitive transactivator of the nuclear import factor importin-α5 (Impα5), and interfering with this mechanism interrupts step-wise differentiation. Underscoring the significance of this axis in vivo, mice with conditional inactivation of gp130 signaling display defective Klf6 and Impα5 expression, OLP maturation arrest and apoptosis, and failure of CNS myelination.

Selecting optimal combinations of transcription factors to promote axon regeneration: Why mechanisms matter

“…Correlative experiments, in which forced expression or knockdown of one TF leads to a change in expression of a second, hint at transcriptional cross-regulation but can’t distinguish direct transcriptional activation from indirect consequences of downstream effector proteins. For instance, in sensory neurons responding to peripheral injury, knockdown of SOX11 leads to reduced ATF3 expression, and in oligodendrocyte precursor cells, activation of STAT3 leads to elevated transcription of KLF6 [35, 41]. These data hint at transcriptional cross-regulation, but a mechanism of direct transcriptional regulation was not established.…”

Karyopherin Alpha Proteins Regulate Oligodendrocyte Differentiation

“…While recent work from our laboratory clearly demonstrates a role for Kpna1 in OL differentiation and viability [24], the current study provides evidence for broader Kpna paralog involvement in OL differentiation. Studies of karyopherins may also inform development of new treatments for disease.…”

“…It is quite possible that it confers CNTF-specific roles, shuttling transcription factors that play a role in Jak-Stat signaling, the major signaling pathway downstream of CNTF [33]. Indeed, Kpna4 has been shown to carry Stat3 as a cargo in other cell types, even independent of its phosphorylated (activated) state [34], and Kpna proteins also carry Klf transcription factors [35,36], such as Klf6, which we have shown to be linked to Jak-Stat signaling in CNS myelination [24]. This suggests that at least one Kpna may have gp130 pathway-specific, or Jak-Stat-specific, functions.…”

“…Mouse OLP were isolated as in [24]. Briefly, cerebral cortices from P6-P8 C57BL6 mice were removed, mechanically dissociated, and then chemically dissociated using papain buffer (1mM MgS0 4 , 20mM Glucose, 2mM EGTA, 2mM NaHCO 3 , 1.65nM l-cysteine, 125U/ml DNase-I (Sigma), 20U/ml Papain (Sigma), in EBSS) for 20 min at 37°C and 5% CO 2 with occasional agitation.…”

“…However, since there are a variety of distinct Kpna paralogs, studying their roles in development and disease may elucidate a set of novel mechanisms regulating gene expression in OLs. Indeed, we recently identified Kpna1 as an important regulator of OL differentiation, inactivation of which disrupts OL maturation and impacts viability [24]. In our recent study, we did not explore potential roles of other Kpna family members in OL development.…”