Delaying histone deacetylase response to injury accelerates conversion into repair Schwann cells and nerve regeneration

ARTICLE Received 30 Mar 2016 | Accepted 14 Dec 2016 | Published 31 Jan 2017 DOI: 10.1038/ncomms14272 OPEN Delaying histone deacetylase response to injury accelerates conversion into repair Schwann cells and nerve regeneration Valérie Brügger1, Mert Duman1, Maëlle Bochud1, Emmanuelle Münger1, Manfred Heller2, Sophie Ruff1 & Claire Jacob1 The peripheral nervous system (PNS) regenerates after injury. However, regeneration is often compromised in the case of large lesions, and the speed of axon reconnection to their target is critical for successful functional recovery. After injury, mature Schwann cells (SCs) convert into repair cells that foster axonal regrowth, and redifferentiate to rebuild myelin. These processes require the regulation of several transcription factors, but the driving mechanisms remain partially understood. Here we identify an early response to nerve injury controlled by histone deacetylase 2 (HDAC2), which coordinates the action of other chromatinremodelling enzymes to induce the upregulation of Oct6, a key transcription factor for SC development. Inactivating this mechanism using mouse genetics allows earlier conversion into repair cells and leads to faster axonal regrowth, but impairs remyelination. Consistently, short-term HDAC1/2 inhibitor treatment early after lesion accelerates functional recovery and enhances regeneration, thereby identifying a new therapeutic strategy to improve PNS regeneration after lesion. 1 Department of Biology, University of Fribourg, Chemin du Musée 10, 1700 Fribourg, Switzerland. 2 Proteomics and Mass Spectrometry Core Facility, Department of Clinical Research, University of Bern, Freiburgstrasse 15, 3010 Bern, Switzerland. Correspondence and requests for materials should be addressed to C.J. (email: ). NATURE COMMUNICATIONS | 8:14272 | DOI: 10.1038/ncomms14272 | www.nature.com/naturecommunications 1 ARTICLE A NATURE COMMUNICATIONS | DOI: 10.1038/ncomms14272 xons of the peripheral nervous system (PNS) have a high capacity of regeneration after lesion, in contrast to axons of the central nervous system (CNS), which poorly regenerate. This is due to intrinsic regenerative properties of PNS neurons, and to a large extent to extrinsic factors that allow and promote axonal regeneration in the PNS1. Schwann cells (SCs), the PNS myelinating glia, hold major functions in creating a favourable environment for axonal regrowth, stimulating axon outgrowth after lesion, and rebuilding myelin sheaths of regenerated axons2. Upon lesion, mature SCs convert into a repair cell phenotype that resembles the immature SC stage in some but not all aspects1–3. Indeed, repair SCs downregulate myelin proteins and pro-myelinating factors such as Krox20 to dedifferentiate and demyelinate, but they also simultaneously activate a repair programme that promotes axonal regrowth and survival, as well as axon debris and myelin removal4. The transcription factor cJun plays a central role in controlling these processes: cJun is strongly upregulated in SCs after a PNS lesion where it induces SC dedifferentiation, the production of neurotrophic and axon survival factors such as GDNF and Artemin, and myelin clearance by SC myelinophagy5–8. Other myelination inhibitors including Sox2, Pax3, Notch, Id2 are also re-expressed in SCs after lesion and are thought to participate in the SC dedifferentiation process4. Once converted into repair cells, SCs proliferate and migrate along damaged axons to organize into bands of Bungner that stimulate axonal regrowth and guide axons back to their former peripheral target. When axons have regrown, SCs downregulate myelination inhibitors and upregulate Krox20 to induce remyelination together with the major transcription factor of SC differentiation Sox10 (ref. 9). In contrast to Krox20, the intermediate inducer of SC differentiation Oct6 is upregulated after lesion and downregulated as SCs redifferentiate10–12. Oct6 is a key transcription factor for PNS development and regeneration, allowing timely myelination and remyelination by inducing Krox20 expression13–15, but needs to be downregulated for myelination to proceed16. Oct6 thus importantly participates in triggering the SC differentiation programme, but also maintains SCs in a pre-myelinating stage. In summary, SC plasticity after lesion requires dynamic regulation of several sets of transcription factors, some inducing SC dedifferentiation or conversion into repair cells, and some triggering SC redifferentiation and remyelination. Mechanisms controlling the regulation of these transcription factors are partially understood. In this study, we set out to elucidate the mechanisms controlling SC conversion into repair cells and redifferentiation after lesion with a focus on chromatinremodelling events. We previously showed that the chromatin-remodelling enzymes histone deacetylase (HDAC)1 and HDAC2 are essential for the specification of neural crest cells into peripheral glia17, for SC survival and myelination during postnatal development18 (also shown by Chen et al.19), and for the maintenance of PNS integrity in adults20. While histone acetyltransferases (HATs) add acetyl groups to histone tails, HDACs remove these acetyl groups. Because acetyl groups neutralize the positive charges of histones, histone acetylation loosens the attraction of negatively charged DNA to histones and thus leads to a more relaxed chromatin structure. In contrast, HDACs allow histones to recover their positive charges, which leads to their tight interaction with DNA, and thus to a more compacted chromatin structure. Because chromatin compaction limits the access for the transcriptional machinery to DNA, HDACs have commonly been thought to act as transcriptional repressors21. However, an increasing number of studies from independent groups reveal that HDACs can also participate in transcriptional activation22–24. Furthermore, HDACs can deacetylate non-histone targets to modify their 2 activity25. Among those, several transcription factors have been described. HDACs are thus very potent transcriptional regulators and their action is highly dependent on their binding partners. Indeed, HDACs cannot bind chromatin directly, but needs to associate with DNA-binding proteins to regulate gene transcription. HDACs are known to belong to different chromatin-remodelling complexes, which often also comprise other chromatin-remodelling enzymes such as histone methyltransferases (HMTs) and demethylases (HDMs)26. In this study, we show that HDAC2 interacts with the transcription factor Sox10 and recruits histone H3 lysine 9 (H3K9) HDMs to form a multifunctional protein complex that de-represses the Sox10 target genes Oct6 and Krox20 to allow their subsequent activation at different time points of the regeneration process after lesion. Interestingly, inactivating this mechanism results in earlier conversion into repair SCs after lesion and faster regeneration, but impairs remyelination. Resu (...truncated)