Targeted stabilization of Munc18‐1 function via pharmacological chaperones

Abstract

Heterozygous de novo mutations in the neuronal protein Munc18-1 cause syndromic neurological symptoms, including severe epilepsy, intellectual disability, developmental delay, ataxia, and tremor. No disease-modifying therapy exists to treat these disorders, and while chemical chaperones have been shown to alleviate neuronal dysfunction caused by mutations in Munc18-1, their required high concentrations and potential toxicity necessitate a Munc18-1targeted therapy. Munc18-1 is essential for neurotransmitter release, and mutations in Munc18-1 have been shown to cause neuronal dysfunction via aggregation and co-aggregation of the wild-type protein, reducing functional Munc18-1 levels well below hemizygous levels. Here, we identify two pharmacological chaperones via structure-based drug design, that bind to wild-type and mutant Munc18-1, and revert Munc18-1 aggregation and neuronal dysfunction in vitro and in vivo, providing the first targeted treatment strategy for these severe pediatric encephalopathies.

Assessing the landscape of STXBP1-related disorders in 534 individuals

“…Based on initial functional data, it has been hypothesized that several recurrent variants may result in either gain-of-function or dominant-negative effects 15 , 40 rather than haploinsufficiency, the generally accepted disease-mechanism in STXBP1 -related disorders. However, when we grouped all variants with known or suspected dominant-negative effects ( n = 35) including p.Arg406His, p.Pro335Leu, p.Pro480Leu and p.Gly544Asp/Val, statistical significance was not reached with regards to clinical similarity and discrete phenotypic associations after correction for multiple comparisons ( Supplementary Fig.…”

Microcircuit failure inSTXBP1encephalopathy leads to hyperexcitability

“…Attempts to rescue the consequences of STXBP1 haploinsufficiency have so far involved compensation for the molecular deficiency, i.e., the lowered STXBP1 expression level. One strategy is to use chemical chaperones, which bind to and stabilize mutant STXBP1, thereby increasing expression levels 10,43 . Other attempts could make use of overexpression of a transgene, or RNA technology to increase expression from the other, normal allele.…”

SNAP25 disease mutations change the energy landscape for synaptic exocytosis due to aberrant SNARE interactions

“…Synaptic phenotypes of Munc18-1 hypoexpression have been identified in the Drosophila neuromuscular junction (Wu et al, 1998), in cultured mouse neurons (Toonen et al, 2006) and in brain slices of STXBP1 heterozygous mice (Chen et al, 2020; dos Santos et al, 2023), as well as in human neurons (Patzke et al, 2015), whereas expression of human missense mutations in STXBP1 null mouse neurons led to synaptic phenotypes for some mutations, but not for others (Kovacevic et al, 2018). Attempts to rescue the disease phenotypes have focused on mechanisms for increasing expression levels, for instance chemical chaperones that might prevent Munc18-1 misfolding and degradation (Abramov et al, 2021b; Guiberson et al, 2018).…”

“…The reason for haploinsufficiency/hypoexpression of most STXBP1 disease mutations has been suggested to be protein instability, leading to degradation (Guiberson et al, 2018;Kovacevic et al, 2018;Martin et al, 2014;Saitsu et al, 2008). Consequently, attempts to rescue the disease phenotypes have focused on mechanisms for increasing general expression levels, for instance chemical chaperones that might prevent Munc18-1 misfolding and degradation (Abramov et al, 2021b;Guiberson et al, 2018).…”