Preservation of neuromuscular function in symptomatic SOD1-G93A mice by peripheral infusion of methylene blue

Neuromuscular Junction as an Entity of Nerve-Muscle Communication

One of the crucial systems severely affected in several neuromuscular diseases is the loss of effective connection between muscle and nerve, leading to a pathological non-communication between the two tissues. The neuromuscular junction (NMJ) represents the critical region at the level of which muscle and nerve communicate. Defects in signal transmission between terminal nerve endings and muscle membrane is a common feature of several physio-pathologic conditions including aging and Amyotrophic Lateral Sclerosis (ALS). Nevertheless, controversy exists on whether pathological events beginning at the NMJ precede or follow loss of motor units. In this review, the role of NMJ in the physio-pathologic interplay between muscle and nerve is discussed.

Histone deacetylase 4 protects from denervation and skeletal muscle atrophy in a murine model of amyotrophic lateral sclerosis

Background

Histone deacetylase 4 (HDAC4) has been proposed as a target for Amyotrophic Lateral Sclerosis (ALS) because it mediates nerve-skeletal muscle interaction and since its expression in skeletal muscle correlates with the severity of the disease. However, our recent studies on the skeletal muscle response upon long-term denervation highlighted the importance of HDAC4 in maintaining muscle integrity.

Methods

To fully identify the yet uncharacterized HDAC4 functions in ALS, we genetically deleted HDAC4 in skeletal muscles of a mouse model of ALS. Body weight, skeletal muscle, innervation and spinal cord were analyzed over time by morphological and molecular analyses. Transcriptome analysis was also performed to delineate the signaling modulated by HDAC4 in skeletal muscle of a mouse model of ALS.

Findings

HDAC4 deletion in skeletal muscle caused earlier ALS onset, characterized by body weight loss, muscle denervation and atrophy, and compromised muscle performance, although the main catabolic pathways were not activated. Transcriptome analysis identified the gene networks modulated by HDAC4 in ALS, revealing UCP1 as a top regulator that may be implicated in worsening ALS features.

Interpretation

HDAC4 plays an important role in preserving innervations and skeletal muscle in ALS, likely by modulating the UCP1 gene network. Our study highlights a possible risk in considering HDAC inhibitors for the treatment of ALS.

Fund

This work was supported by FIRB grant (RBFR12BUMH) from Ministry of Education, Universities and Research, by Fondazione Veronesi, by Sapienza research project 2017 (RM11715C78539BD8) and Polish National Science Center grant (UMO-2016/21/B/NZ3/03638).

Regulation of HSF1 protein stabilization: An updated review

Heat shock factor 1 (HSF1) is a transcriptional factor that determines the efficiency of heat shock responses (HSRs) in the cell. Given its function has been extensively studied in recent years, HSF1 is considered a potential target for the treatment of disorders associated with protein aggregation. The activity of HSF1 is traditionally regulated at the transcriptional level in which the transactivation domain of HSF1 is modified by extensive array of pos-translational modifications, such as phosphorylation, sumoylation, and acetylation. Recently, HSF1 is also reported to be regulated at the monomeric level. For example, in neurodegenerative disorders such as Huntington's disease and Alzheimer's disease the expression levels of the monomeric HSF1 are found to be reduced markedly. Methylene blue (MB) and riluzole, two clinical available drugs, increase the amount of the monomeric HSF1 in both cells and animals. Since the monomeric HSF1 not only determines the efficiency of HSRs, but exerts protective effects in a trimerization-independent manner, increasing the amount of the monomeric HSF1 via stabilization of HSF1 may be an alternative strategy for the amplification of HSR. However, to date we have no outlined knowledges about HSF1 protein stabilization, though studies regarding the regulation of the monomeric HSF1 have been documented in recent years. Here, we summarize the regulation of the monomeric HSF1 by some previously reported factors, such as synuclein, Huntingtin (Htt), TDP-43, unfolded protein response (UPR), MB and doxorubicin (DOX), as well as their possible mechanisms, aiming to push the understanding about HSF1 protein stabilization.