Titin M-line insertion sequence 7 is required for proper cardiac function in mice

ABSTRACT Titin is a giant sarcomeric protein that is involved in a large number of functions, with a primary role in skeletal and cardiac sarcomere organization and stiffness. The titin gene (TTN) is subject to various alternative splicing events, but in the region that is present at the M-line, the only exon that can be spliced out is Mex5, which encodes for the insertion sequence 7 (is7). Interestingly, in the heart, the majority of titin isoforms are Mex5+, suggesting a cardiac role for is7. Here, we performed comprehensive functional, histological, transcriptomic, microscopic and molecular analyses of a mouse model lacking the Ttn Mex5 exon (ΔMex5), and revealed that the absence of the is7 is causative for dilated cardiomyopathy. ΔMex5 mice showed altered cardiac function accompanied by increased fibrosis and ultrastructural alterations. Abnormal expression of excitation–contraction coupling proteins was also observed. The results reported here confirm the importance of the C-terminal region of titin in cardiac function and are the first to suggest a possible relationship between the is7 and excitation–contraction coupling. Finally, these findings give important insights for the identification of new targets in the treatment of titinopathies.

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hnRNP U protein is required for normal pre-mRNA splicing and postnatal heart development and function

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1508461112 ◽

2015 ◽

Vol 112 (23) ◽

pp. E3020-E3029 ◽

Cited By ~ 47

Author(s):

Junqiang Ye ◽

Nadine Beetz ◽

Sean O’Keeffe ◽

Juan Carlos Tapia ◽

Lindsey Macpherson ◽

...

Keyword(s):

Alternative Splicing ◽

Heart Development ◽

Specific Protein ◽

Protein Product ◽

Conclusive Evidence ◽

Mrna Splicing ◽

Excitation Contraction Coupling ◽

Contraction Coupling ◽

Hnrnp U ◽

And Function

We report that mice lacking the heterogeneous nuclear ribonucleoprotein U (hnRNP U) in the heart develop lethal dilated cardiomyopathy and display numerous defects in cardiac pre-mRNA splicing. Mutant hearts have disorganized cardiomyocytes, impaired contractility, and abnormal excitation–contraction coupling activities. RNA-seq analyses of Hnrnpu mutant hearts revealed extensive defects in alternative splicing of pre-mRNAs encoding proteins known to be critical for normal heart development and function, including Titin and calcium/calmodulin-dependent protein kinase II delta (Camk2d). Loss of hnRNP U expression in cardiomyocytes also leads to aberrant splicing of the pre-mRNA encoding the excitation–contraction coupling component Junctin. We found that the protein product of an alternatively spliced Junctin isoform is N-glycosylated at a specific asparagine site that is required for interactions with specific protein partners. Our findings provide conclusive evidence for the essential role of hnRNP U in heart development and function and in the regulation of alternative splicing.

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Polyglutamine-expanded androgen receptor disrupts muscle triad, calcium dynamics and the excitation-contraction coupling gene expression program

10.1101/618405 ◽

2019 ◽

Author(s):

M Chivet ◽

C Marchioretti ◽

M Pirazzini ◽

D Piol ◽

C Scaramuzzino ◽

...

Keyword(s):

Gene Expression ◽

Androgen Receptor ◽

Muscle Contraction ◽

Experimental Evidence ◽

Muscle Function ◽

Muscle Force ◽

Primary Role ◽

Regulation Of Expression ◽

Excitation Contraction Coupling ◽

Contraction Coupling

AbstractSpinal and bulbar muscular atrophy (SBMA) is caused by polyglutamine (polyQ) expansions in the androgen receptor (AR) gene. Although clinical and experimental evidence highlight a primary role for skeletal muscle in the onset, progression, and outcome of disease, the pathophysiological and molecular processes underlying SBMA muscle atrophy are poorly understood. Here we show that polyQ-expanded AR alters intrinsic muscle force generation before denervation. Reduced muscle force was associated with a switch in fiber-type composition, disrupted muscle striation, altered calcium (Ca++) dynamics in response to muscle contraction, and aberrant expression of excitation-contraction coupling (ECC) machinery genes in transgenic, knock-in and inducible SBMA mice and patients. Importantly, treatment to suppress polyQ-expanded AR toxicity restored ECC gene expression back to normal. Suppression of AR activation by surgical castration elicited similar ECC gene expression changes in normal mice, suggesting that AR regulates the expression of these genes in physiological conditions. Bioinformatic analysis revealed the presence of androgen-responsive elements on several genes involved in muscle function and homeostasis, and experimental evidence showed AR-dependent regulation of expression and promoter occupancy of the most up-regulated gene from transcriptomic analysis in SBMA muscle, i.e. sarcolipin, a key ECC gene. These observations reveal an unpredicted role for AR in the regulation of expression of genes involved in muscle contraction and Ca++ dynamics, a level of muscle function regulation that is disrupted in SBMA muscle, yet restored by pharmacologic treatment.

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