A new potential therapeutic strategy for Steinert’s disease
The laboratories of Luc Willems (GIGA-Cancer) and Vincent Seutin (GIGA-Neurosciences) have just published the results of a former PhD student, Florent Porquet, in collaboration with the laboratory of Denis Furling at the « Institut de Myologie » in Paris. Their study establishes the scientific basis of a new therapeutic strategy for Steinert’s disease.
This disease, also called type 1 myotonic dystrophy (DM1), is due to an abnormal repetition of CTG codons in the non-coding region of the gene called « DM1 protein kinase » or DMPK. This induces a massive accumulation of the corresponding mRNA in the nucleus, which deregulates enzymes involved in the maturation (« splicing ») of RNAs such as MBNL. In turn, this makes many cell types dysfunctional. DM1 patients suffer from muscle weakness and an inability to relax the muscle after its contraction (« myotonia »). They also suffer from other symptoms due to dysfunction of the nervous system (excessive daytime sleepiness, altered executive functions) and other organs (cardiomyopathy, cataract, diabetes). It is therfore a multiorgan disease.
Several strategies have been used previously in order to reduce the deleterious effects of the pathological mRNA, such as using antisense nucleotides or small molecules that could cleave it.
Since the DMPK gene appears to be dispensable in mammals (KO mouse for DMPK have a normal phenotype, probably because of compensation), researchers tried to inhibit the transcription of DMPK using CRISPRi. This technique consists of using single guide RNAs coupled to a « dead » CAS-9 and to KRAB. The strategy worked. The results show the remarkable selectivity of this approach on the affected gene and its ability to restore some functions of human DM1 muscle cells in vitro.
The transcriptomic analysis carried out by the GIGA platform indeed demonstrated that some guide RNAs used are perfectly specific, in that the expression of no other gene than DMPK was affected.
This study involved very different and complementary expertises. Most of the molecular work was done by Florent Porquet in the Willems laboratory. The patch clamp technique was used by L. Weidong in the Seutin laboratory to examine the effect of the therapeutic strategy on a functional read-out, namely the excitability of myocytes. The results show that the strategy reverses the hyperexcitability of DM1 myocytes.
The whole study was carried out in vitro. It is now important to evaluate to what extent this strategy can work in vivo, taking into accounts various constraints (maximal possible size of the plasmids as a function of the type of virus that should be used, ability of the viruses to enter various cell types). It will also be critical to evaluate whether the splicing ability of affected cells will be corrected sufficiently.
Porquet F, Weidong L, Jehasse K, Gazon H, Kondili M, Blacher S, Massotte L, Di Valentin E, Furling D, Gillet NA, Klein AF*, Seutin V*, Willems L*
Mol Ther Nucleic acids 32, 857-871 (2023) doi: 10.1016/j.omtn.2023.05.007. eCollection 2023 Jun 13. (*equal participation of three last authors)