Muscleblind-like 3 deficit results in a spectrum of age-associated pathologies observed in myotonic dystrophy

Abstract

Myotonic dystrophy type I (DM1) exhibits distinctive disease specific phenotypes and the accelerated onset of a spectrum of age-associated pathologies. In DM1, dominant effects of expanded CUG repeats result in part from the inactivation of the muscleblind-like (MBNL) proteins. To test the role of MBNL3, we deleted Mbnl3 exon 2 (Mbnl3ΔE2) in mice and examined the onset of age-associated diseases over 4 to 13 months of age. Accelerated onset of glucose intolerance with elevated insulin levels, cardiac systole deficits, left ventricle hypertrophy, a predictor of a later onset of heart failure and the development of subcapsular and cortical cataracts is observed in Mbnl3ΔE2 mice. Retention of embryonic splice isoforms in adult organs, a prominent defect in DM1, is not observed in multiple RNAs including the Insulin Receptor (Insr), Cardiac Troponin T (Tnnt2), Lim Domain Binding 3 (Ldb3) RNAs in Mbnl3ΔE2 mice. Although rare DM1-like splice errors underlying the observed phenotypes cannot be excluded, our data in conjunction with the reported absence of alternative splice errors in embryonic muscles of a similar Mbnl3ΔE2 mouse by RNA-seq studies, suggest that mechanisms distinct from the adult retention of embryonic splice patterns may make important contributions to the onset of age-associated pathologies in DM1.

MBNL splicing activity depends on RNA binding site structural context

“…Since the presence of three MBNL paralogs was discovered ( 13 , 70 ), much attention has focused on determining the cellular functions and distinguishable features of these paralogs. In contrast to a previously described antagonistic effect of MBNL3 on MBNL1 activity ( 13 , 17 , 71 ), in the current study, we discovered a competitive interaction between MBNL paralogs and their isoforms that is determined by the organization of RNA regulatory elements and modulates AS profile (Figure 6 ). Initially, we observed that the loss of MBNL3 in myoblasts promotes the MBNL-mediated splicing profile (Figure 6 ).…”

“…Initially, we observed that the loss of MBNL3 in myoblasts promotes the MBNL-mediated splicing profile (Figure 6 ). This splicing phenomenon was not evident either in adult heart or muscles of Mbnl3 KO mice, probably due to the relatively low contribution of MBNL3 to the total pool of MBNL in adult tissues ( 17 ). However, while MBNL3 predominates in cells lacking MBNL1 and MBNL2, the paralog shifts the AS profile towards MBNL-induced (Figure 6 and Supplementary Figure S11 ) what confirms a convergent splicing activity of MBNL paralogs and suggests their competitive interaction while present concomitantly in cells.…”

Targeted Genetic Screen in Amyotrophic Lateral Sclerosis Reveals Novel Genetic Variants with Synergistic Effect on Clinical Phenotype

“…A logical consequence of this hypothesis is that loss-of-function mutations in G4C2-binding partners might contribute to ALS pathogenesis independently of and/or act synergistically with C9ORF72 expansions. Evidence in myotonic dystrophy supports this hypothesis: mutations in muscleblind-like proteins modify the phenotype caused by sequestration of the same proteins by CUG-repeat RNA (e.g., Choi et al, 2016 ). Similarly mice lacking muscleblind-like 1 exhibit some of the features of myotonic dystrophy despite the absence of CUG-repeat RNA (Dixon et al, 2015 ).…”

Correction of RNA-Binding Protein CUGBP1 and GSK3β Signaling as Therapeutic Approach for Congenital and Adult Myotonic Dystrophy Type 1

“…SMN1 (spinal motor neuron 1) is associated with the maintenance of the motor neurons [85]. MBNL3 belongs to a family of MBNL proteins that are affected in DM [86][87][88]. Misregulation of CUGBP1 in DM1 might affect these mRNAs (directly or indirectly); therefore, the number of genes, disrupted by CUGBP1 in DM1, might be great because each of these RNA-binding proteins controls own sets of mRNAs.…”