We thus demonstrate that HDAC6 is a new FoxO3-dependent player in muscle atrophy. == MATERIALS AND METHODS == == == == == == Patients Biopsies == IL12RB2 Patient muscle samples were analyzed from surgical biopsies of the deltod muscle primarily performed for diagnosis purpose. muscle protein ubiquitination and degradation during atrophy. HDAC6 is a particular HDAC, Lerociclib dihydrochloride which is functionally related to the ubiquitin proteasome system via its ubiquitin binding domain. We show thatHDAC6is up-regulated during muscle atrophy. HDAC6 activation is dependent on the transcription factor FoxO3a, and the inactivation Lerociclib dihydrochloride of HDAC6 in mice Lerociclib dihydrochloride protects against muscle wasting. HDAC6 is able to interact with MAFbx, a key ubiquitin ligase involved in muscle atrophy. Our findings demonstrate the implication of HDAC6 in skeletal muscle wasting and identify HDAC6 as a new downstream target of FoxO3a in stress response. This work provides new insights in skeletal muscle atrophy development and opens interesting perspectives on HDAC6 as a valuable marker of muscle atrophy and a potential target for pharmacological treatments. == Introduction == Skeletal muscle atrophy results in a massive muscle mass loss and it is characterized by a decrease in the size of pre-existing muscle fibers. Muscle atrophy can occur as a result of simple inactivity and aging or can be associated with various pathologies such as myopathies, hyperthyroidism, AIDS, or cancer (1). Throughout the past 30 years, the prevention of muscle wasting has been a major issue both due to muscle atrophy being associated with multiple pathologies and to its tendency to severely impair the daily life of afflicted patients (2). Among the effectors of skeletal muscle atrophy, massive protein degradation by the ubiquitin-proteasome pathway and autophagy (3) play a pivotal role. Significant advances have been made in the understanding of muscle wasting through the identification of specific factors involved in the process and with the identification of common pathways shared by all types of muscle atrophy. The genes encoding such factors are referred to asatrogenes. The first to be identified were the E3 ubiquitin ligases MAFbx/Atrogin-1 and MuRF1. The expression of these two genes is up-regulated in all models of muscle atrophy, and their inactivation significantly reduces muscles wasting Lerociclib dihydrochloride (4, 5). The up-regulation of these atrogenes during muscle atrophy depends on the activation of specific transcription factors of the Forkhead box O (FoxO)3family (6, 7) (their expression being activated during muscle atrophy and their activity being controlled by the Akt kinase). In normal conditions, phosphorylation of such factors by Akt prevents their translocation in the nucleus. In pro-atrophic conditions, Akt activity decreases, thus reducing FoxO phosphorylation and allowing its entry into the nucleus to activate its target genes (7). The muscle-specific transcription factor Myogenin also regulates MAFbx and MuRF1 expression: upon denervation, Myogenin expression is strongly up-regulated and participates in the activation of the two ubiquitin ligases (8). Histone deacetylases (HDACs) are central regulators of gene expression. HDAC1 regulates the expression of the acetylcholine receptor in response to neural factors (9), whereas HDAC4 and HDAC9 together with HDAC1 and HDAC3 participate in the regulation of AChR expression by electrical activity via the control of myogenin expression (10, 11). Recently, it was shown that HDACs are also involved in the regulation of atrogenes via Myogenin and FoxO transcription factors. FoxO3 association with the acetyltransferase p300 and subsequent acetylation induces its cytoplasmic translocation and degradation. Conversely, FoxO3 deacetylation is associated with transcriptional activation (12). Myogenin activation also involves HDAC4. HDAC4 is required for Myogenin activation and therefore participates in the activation of MAFbx during muscle atrophy induced by denervation (8). The present study is based on our observation that the expression of another histone deacetylase, HDAC6, is up-regulated during skeletal muscle atrophy both in mouse and human. HDAC6 is a peculiar HDAC: mostly cytoplasmic, it deacetylates Tubulin, Cortactin and Hsp90 (rather than histones) and it contains an ubiquitin binding motif (13). In addition , HDAC6 interacts with components of the ubiquitin proteasome pathway (14) and has been shown to regulate ubiquitin-dependent cellular processes (15, 16). Altogether, these evidences suggested that HDAC6 could be involved in regulation or degradation of muscle atrophy.