Amino acid mutations in the caldesmon COOH-terminal functional domain increase force generation in bladder smooth muscle

Abstract

Caldesmon (CaD), a component of smooth muscle thin filaments, binds actin, tropomyosin, calmodulin, and myosin and inhibits actin-activated ATP hydrolysis by smooth muscle myosin. Internal deletions of the chicken CaD functional domain that spans from amino acids (aa) 718 to 731, which corresponds to aa 512-530 including the adjacent aa sequence in mouse CaD, lead to diminished CaD-induced inhibition of actin-activated ATP hydrolysis by myosin. Transgenic mice with mutations of five aa residues (Lys(523) to Gln, Val(524) to Leu, Ser(526) to Thr, Pro(527) to Cys, and Lys(529) to Ser), which encompass the ATPase inhibitory determinants located in exon 12, were generated by homologous recombination. Homozygous (-/-) animals did not develop, but heterozygous (+/-) mice carrying the expected mutations in the CaD ATPase inhibitory domain (CaD mutant) matured and reproduced normally. The peak force produced in response to KCl and electrical field stimulation by the detrusor smooth muscle from the CaD mutant was high compared with that of the wild type. CaD mutant mice revealed nonvoiding contractions during bladder filling on awake cystometry, suggesting that the CaD ATPase inhibitory domain suppresses force generation during the filling phase and this suppression is partially released by mutations in 50% of CaD in heterozygous. Our data show for the first time a functional phenotype, at the intact smooth muscle tissue and in vivo organ levels, following mutation of a functional domain at the COOH-terminal region of CaD.

Caldesmon ablation in mice causes umbilical herniation and alters contractility of fetal urinary bladder smooth muscle

“…S2 ). In this context, it is interesting to note that point mutations in the C terminus of CaD in a mouse model, which did not lower CaD expression levels but interfered with the inhibition on cross-bridge cycling, increased force ( Deng et al, 2013 ) similar to the observed increased force in HETs in our study.…”

“…In visceral smooth muscles, l-CaD expression was up-regulated, which may compensate for the loss of h-CaD ( Guo et al, 2013 ). In another mouse model, the introduction of five point mutations within the C terminus of CaD, which encompassed the ATPase inhibitory determinants, resulted in a lethal phenotype in homozygous but not heterozygous (HET) mice ( Deng et al, 2013 ). Adult HET mice displayed nonvoiding contractions during urinary bladder filling.…”

Effect of caldesmon mutations in the development of zebrafish embryos

“…However, in a model with homozygous loss of h-caldesmon, the loss is shown not to be lethal [28,29]. Another mouse model with mutations targeting a functional domain in both isoforms is lethal as a homozygote but reproduces normally as a heterozygote [30]. The severe cardiovascular defects are not described in Cald1-deficient mice, although the underlying causes of pre-and postnatal lethality are not fully understood [28][29][30].…”

Does altered myogenic activity contribute to OAB symptoms from detrusor overactivity? ICI-RS 2013

“…This action of caldesmon should be important to maintain bladder relaxation during filling. Recently, it has been demonstrated that mice with mutations in the caldesmon gene that encompass the ATPase inhibitory domain show non‐voiding contractions during awake cystometry . However, it is not yet clear if this effect is likely to underlie pathological increases of bladder dysfunction as the action of caldesmon on actin–myosin interaction is only observed at basal levels of MLC 20 phosphorylation.…”