Impact of histone deacetylase inhibition and arimoclomol on heat shock protein expression and disease biomarkers in primary culture models of familial ALS.

Protein misfolding and mislocalization are common themes in neurodegenerative disorders, including motor neuron disease, and amyotrophic lateral sclerosis (ALS). Maintaining proteostasis is a crosscutting therapeutic target, including the upregulation of heat shock proteins (HSP) to increase chaperoning capacity. Motor neurons have a high threshold for upregulating stress-inducible HSPA1A, but constitutively express high levels of HSPA8. This study compared the expression of these HSPs in cultured motor neurons expressing three variants linked to familial ALS: TAR DNA binding protein 43 kDa (TDP-43)G348C, fused in sarcoma (FUS)R521G, or superoxide dismutase I (SOD1)G93A. All variants were poor inducers of Hspa1a, and reduced levels of Hspa8 mRNA and protein, indicating multiple compromises in chaperoning capacity. To promote HSP expression, cultures were treated with the putative HSP coinducer, arimoclomol, and class I histone deacetylase inhibitors, to promote active chromatin for transcription, and with the combination. Treatments had variable, often different effects on the expression of Hspa1a and Hspa8, depending on the ALS variant expressed, mRNA distribution (somata and dendrites), and biomarker of toxicity measured (histone acetylation, maintaining nuclear TDP-43 and the neuronal Brm/Brg-associated factor chromatin remodeling complex component Brg1, mitochondrial transport, FUS aggregation). Overall, histone deacetylase inhibition alone was effective on more measures than arimoclomol. As in the FUS model, arimoclomol failed to induce HSPA1A or preserve Hspa8 mRNA in the TDP-43 model, despite preserving nuclear TDP-43 and Brg1, indicating neuroprotective properties other than HSP induction. The data speak to the complexity of drug mechanisms against multiple biomarkers of ALS pathogenesis, as well as to the importance of HSPA8 for neuronal proteostasis in both somata and dendrites.

Reversal of cognitive deficits in FUSR521G amyotrophic lateral sclerosis mice by arimoclomol and a class I histone deacetylase inhibitor independent of heat shock protein induction.

Protein misfolding and mislocalization are common to both familial and sporadic forms of amyotrophic lateral sclerosis (ALS). Maintaining proteostasis through induction of heat shock proteins (HSP) to increase chaperoning capacity is a rational therapeutic strategy in the treatment of ALS. However, the threshold for upregulating stress-inducible HSPs remains high in neurons, presenting a therapeutic obstacle. This study used mouse models expressing the ALS variants FUSR521G or SOD1G93A to follow up on previous work in cultured motor neurons showing varied effects of the HSP co-inducer, arimoclomol, and class I histone deacetylase (HDAC) inhibitors on HSP expression depending on the ALS variant being expressed. As in cultured neurons, neither expression of the transgene nor drug treatments induced expression of HSPs in cortex, spinal cord or muscle of FUSR521G mice, indicating suppression of the heat shock response. Nonetheless, arimoclomol, and RGFP963, restored performance on cognitive tests and improved cortical dendritic spine densities. In SOD1G93A mice, multiple HSPs were upregulated in hindlimb skeletal muscle, but not in lumbar spinal cord with the exception of HSPB1 associated with astrocytosis. Drug treatments improved contractile force but reduced the increase in HSPs in muscle rather than facilitating their expression. The data point to mechanisms other than amplification of the heat shock response underlying recovery of cognitive function in ALS-FUS mice by arimoclomol and class I HDAC inhibition and suggest potential benefits in counteracting cognitive impairment in ALS, frontotemporal dementia and related disorders.