HDAC1 and HDAC2 control the transcriptional program of myelination and the survival of Schwann cells

Histone deacetylases (HDACs) are major epigenetic regulators. We show that HDAC1 and HDAC2 functions are critical for myelination of the peripheral nervous system. Using mouse genetics, we have ablated Hdac1 and Hdac2 specifically in Schwann cells, resulting in massive Schwann cell loss and virtual absence of myelin in mutant sciatic nerves. Expression of Sox10 and Krox20, the main transcriptional regulators of Schwann cell myelination, was greatly reduced. We demonstrate that in Schwann cells, HDAC1 and HDAC2 exert specific primary functions: HDAC2 activates the transcriptional program of myelination in synergy with Sox10, whereas HDAC1 controls Schwann cell survival by regulating the levels of active beta-catenin

Dicer in Schwann cells is required for myelination and axonal integrity

Dicer is responsible for the generation of mature micro-RNAs (miRNAs) and loading them into RNA-induced silencing complex (RISC). RISC functions as a probe that targets mRNAs leading to translational suppression and mRNA degradation. Schwann cells (SCs) in the peripheral nervous system undergo remarkable differentiation both in morphology and gene expression patterns throughout lineage progression to myelinating and nonmyelinating phenotypes. Gene expression in SCs is particularly tightly regulated and critical for the organism, as highlighted by the fact that a 50% decrease or an increase to 150% of normal gene expression of some myelin proteins, like PMP22, results in peripheral neuropathies. Here, we selectively deleted Dicer and consequently gene expression regulation by mature miRNAs from Mus musculus SCs. Our results show that in the absence of Dicer, most SCs arrest at the promyelinating stage and fail to start forming myelin. At the molecular level, the promyelinating transcription factor Krox20 and several myelin proteins [including myelin associated glycoprotein (MAG) and PMP22] were strongly reduced in mutant sciatic nerves. In contrast, the myelination inhibitors SOX2, Notch1, and Hes1 were increased, providing an additional potential basis for impaired myelination. A minor fraction of SCs, with some peculiar differences between sensory and motor fibers, overcame the myelination block and formed unusually thin myelin, in line with observed impaired neuregulin and AKT signaling. Surprisingly, we also found signs of axonal degeneration in Dicer mutant mice. Thus, our data indicate that miRNAs critically regulate Schwann cell gene expression that is required for myelination and to maintain axons via axon- glia interactions. Copyrigh

HDAC1/2-dependent P0 expression maintains paranodal and nodal integrity independently of myelin stability through interactions with neurofascins

The pathogenesis of peripheral neuropathies in adults is linked to maintenance mechanisms that are not well understood. Here, we elucidate a novel critical maintenance mechanism for Schwann cell (SC)-axon interaction. Using mouse genetics, ablation of the transcriptional regulators histone deacetylases 1 and 2 (HDAC1/2) in adult SCs severely affected paranodal and nodal integrity and led to demyelination/remyelination. Expression levels of the HDAC1/2 target gene myelin protein zero (P0) were reduced by half, accompanied by altered localization and stability of neurofascin (NFasc)155, NFasc186, and loss of Caspr and septate-like junctions. We identify P0 as a novel binding partner of NFasc155 and NFasc186, both in vivo and by in vitro adhesion assay. Furthermore, we demonstrate that HDAC1/2-dependent P0 expression is crucial for the maintenance of paranodal/nodal integrity and axonal function through interaction of P0 with neurofascins. In addition, we show that the latter mechanism is impaired by some P0 mutations that lead to late onset Charcot-Marie-Tooth disease

Data from: HDAC1/2-dependent P0 expression maintains paranodal and nodal integrity independently of myelin stability through interactions with neurofascins

The pathogenesis of peripheral neuropathies in adults is linked to maintenance mechanisms that are not well understood. Here, we elucidate a novel critical maintenance mechanism for Schwann cell (SC)–axon interaction. Using mouse genetics, ablation of the transcriptional regulators histone deacetylases 1 and 2 (HDAC1/2) in adult SCs severely affected paranodal and nodal integrity and led to demyelination/remyelination. Expression levels of the HDAC1/2 target gene myelin protein zero (P0) were reduced by half, accompanied by altered localization and stability of neurofascin (NFasc)155, NFasc186, and loss of Caspr and septate-like junctions. We identify P0 as a novel binding partner of NFasc155 and NFasc186, both in vivo and by in vitro adhesion assay. Furthermore, we demonstrate that HDAC1/2-dependent P0 expression is crucial for the maintenance of paranodal/nodal integrity and axonal function through interaction of P0 with neurofascins. In addition, we show that the latter mechanism is impaired by some P0 mutations that lead to late onset Charcot-Marie-Tooth disease

Underlying data main and supplementary figures

2 Excel files with underlying data of Figs. 1CEFGH, 2AD, 3AGH, 4AB, 5BEGI, 6F, 7F, 9BE, S1ABC, S2BCD, S3ABCDE, S5, S6A, S7BC, S17BE, S18, and 2 video for Fig 1

In contrast to the S49L P0 mutant, D32G and H52Y P0 mutants rescue myelination of HDAC1/2 <i>plp</i>-dKO DRG but not paranodal/nodal integrity.

<p>Coimmunofluorescence of MBP (red) and (A) neurofilament (NF, green), and Myc or GFP fluorescence (blue), or (C) neurofascins (NFasc, green), or (D) Caspr (green) in myelinated HDAC1/2 <i>plp</i>-dKO DRG cultures transduced with lentiviruses expressing either GFP, H52Y-myc, D32G-myc, S49L-myc or P0-myc, and treated with tamoxifen for 10 d after completion of myelination. A–B show that H52Y and D32G but not S49L P0 mutants are able to rescue myelination of <i>plp</i>-dKO DRG cultures, similarly to P0-myc, and C–D show that S49L, but not H52Y or D32G, P0 mutant is able to partially rescue paranodal/nodal defects of <i>plp</i>-dKO DRG cultures. In (C), pictures on the right are magnifications of the white boxes depicted on left images. Arrows indicate paranodes/nodes. In (B), quantification of MBP fluorescence intensity normalized to NF and compared to GFP or P0-myc (set to 1). DRG of six <i>plp</i>-dKO embryos were quantified (three <i>plp</i>-dKO embryos per graph, four coverslips per <i>plp</i>-dKO). In (C,D), DRG of three <i>plp</i>-dKO embryos were analyzed and representative pictures are shown. In (E), the graph represents the percentage of intact (Caspr-positive or high NFasc levels) nodes and heminodes. DRG of three <i>plp</i>-dKO embryos were quantified, four coverslips per <i>plp</i>-dKO, 80 to 300 nodes/heminodes counted per <i>plp</i>-dKO per virus. <i>P</i>-values (paired (B) and unpaired (E) two-tailed (unless stated otherwise in the figure) Student's <i>t</i> test): * = <i>p</i> < 0.05, ** = <i>p</i> < 0.01, error bars = SEM.</p