CapZ dynamics are altered by endothelin-1 and phenylephrine via PIP2- and PKC-dependent mechanisms

Abstract

One of the unanswered questions in muscle hypertrophy is how new contractile units are inserted into a stable existing cytoskeletal meshwork. Regulation of actin capping by CapZ may play a role in remodeling processes, therefore, CapZ dynamics are determined during rapid growth of cardiac cells in vitro. Neonatal rat ventricular myocytes were infected with adenovirus expressing green fluorescent protein-CapZ beta1 and responded normally to hypertrophic stimuli. CapZ dynamics were analyzed by fluorescence recovery after photobleaching in cultured myocytes treated with endothelin-1 (100 nM) or phenylephrine (10 muM). Recovery by 30 s was greater with endothelin treatment. Analysis 30 min postbleach showed CapZ-infected cells treated with endothelin recovered more completely than controls (77 +/- 9% vs. 50 +/- 6%, P < 0.001). Similar results were found with phenylephrine (77 +/- 5%, P < 0.05). A potential mechanism for phosphatidylinositol bisphosphate (PIP2) mediation of increased CapZ exchange in endothelin- and phenylephrine-treated cells was tested. PIP2 sequestration with neomycin (500 muM) blocked both endothelin- (43 +/- 6%, P < 0.001) and phenylephrine (36 +/- 4%, P < 0.001)-mediated recovery. The protein kinase C inhibitor chelerythrine chloride (10 muM) also blocked endothelin- (53 +/- 10%, P < 0.001) and phenylephrine (42 +/- 3%, P < 0.001)-mediated recovery. This study demonstrates for the first time that endothelin and phenylephrine alter CapZ dynamics through PIP2- and PKC-dependent pathways, which might destabilize the existing framework and permit sarcomeric remodelling to proceed.

Aciculin interacts with filamin C and Xin and is essential for myofibril assembly, remodeling and maintenance

“…Here, we demonstrate that the Xin-aciculin complex, as revealed by BiFC, is localized at FLNc-containing sites during EPS-induced muscle remodeling and seems to be involved in myofibril repair. FRAP of unstimulated myotubes revealed extremely high dynamics and mobility of aciculin compared to other sarcomeric proteins (da Silva Lopes et al, 2011;Hartman et al, 2009;Wang et al, 2005;Wang et al, 2011), both at Z-discs and premyofibrils. Application of EPS even further increased aciculin dynamics (Fig.…”

“…4). Similarly, contractility stimulation or application of hormones enhances turnover of CapZ in cardiomyocytes (Hartman et al, 2009;Lin et al, 2013).…”

The sarcomeric cytoskeleton: from molecules to motion

“…CapZ was also found to be regulated by PIP2, where PIP2 decreases its affinity to F-actin (Heiss and Cooper, 1991). Exercise-induced changes in PIP2 levels dynamically regulate the exchange of CapZ at the Z-disk (Hartman et al, 2009;Lin et al, 2013), not dissimilar to the regulation of α-actinin (Ribeiro et al, 2014). But are these PIP2-regulated proteins alone in regulating actin dynamics at the nascent or remodelling Z-disk?…”

Dynamics of Actin in the Heart: Defining Thin Filament Length

“…Treatment of isolated cardiomyocytes with endothelin-1 (ET1) or phenylephrine (PE), which induce cellular hypertrophy, decreases the affinity of CapZ for the barbed end. An exciting hypothesis based on this investigation is that increased exchange of CapZ may destabilize the Z-disc and facilitate insertion of new sarcomeres during hypertrophic remodeling through phosphatidylinositol-4,5-bisphosphate (PIP2) and protein kinase-C (PKC)-dependent pathways (Hartman et al 2009). Following short, mechanical strain (to mimic exercise), CapZ capping is decreased and actin dynamics is increased in cardiomyocytes, which was proposed to be an adaptive hypertrophy response to add new sarcomeres (Fig.…”