The actin-organizing formin protein Fhod3 is required for postnatal development and functional maintenance of the adult heart in mice

Abstract

Cardiac development and function require actin-myosin interactions in the sarcomere, a highly organized contractile structure. Sarcomere assembly mediated by formin homology 2 domain-containing 3 (Fhod3), a member of formins that directs formation of straight actin filaments, is essential for embryonic cardiogenesis. However, the role of Fhod3 in the neonatal and adult stages has remained unknown. Here, we generated floxed mice to bypass the embryonic lethality of an knockout (KO). Perinatal KO of in the heart caused juvenile lethality at around day 10 after birth with enlarged hearts composed of severely impaired myofibrils, indicating that Fhod3 is crucial for postnatal heart development. Tamoxifen-induced conditional KO of in the adult heart neither led to lethal effects nor did it affect sarcomere structure and localization of sarcomere components. However, adult -deleted mice exhibited a slight cardiomegaly and mild impairment of cardiac function, conditions that were sustained over 1 year without compensation during aging. In addition to these age-related changes, systemic stimulation with the α1-adrenergic receptor agonist phenylephrine, which induces sustained hypertension and hypertrophy development, induced expression of fetal cardiac genes that was more pronounced in adult-deleted mice than in the control mice, suggesting that Fhod3 modulates hypertrophic changes in the adult heart. We conclude that Fhod3 plays a crucial role in both postnatal cardiac development and functional maintenance of the adult heart.

Fhod1, an actin‐organizing formin family protein, is dispensable for cardiac development and function in mice

“…The adult heart of Fhod1 KO mice showed apparently normal sarcomeric structures composed of the Z-line (marked with the antibody to α-actinin) and thin actin filaments (stained with phalloidin; Figure 4a). This is in striking contrast to Fhod3 depletion, which causes disruption of sarcomeres (Kan-o et al, 2012;Ushijima et al, 2018). Furthermore, we paid special attention to the intercalated discs, specialized cell-cell contacts in the heart, since Fhod1 has been reported to be accumulated at intercalated discs (Al Haj et al, 2015;Dwyer et al, 2014).…”

“…Fhod3 is highly expressed in the heart and also in the kidney and brain, but to a lesser extent (Kanaya et al, ). In line with this expression pattern, Fhod3 plays an essential role in assembly of actin into myofibrils in cardiomyocytes (Iskratsch et al, ; Taniguchi et al, ), which was subsequently verified at the whole heart level by the analysis of conventional and conditional Fhod3‐knockouot mice (Kan‐o et al, ; Ushijima et al, ). The critical roles of Fhod3 in regulation of actin assembly in the heart is further supported by the clinical observations that genetic variants of Fhod3 are associated with hypertrophic and dilated cardiomyopathies (Arimura et al, ; Wooten et al, ).…”

“…Immunoblot analysis was performed as previously described (Ushijima et al, ). Briefly, the adult hearts of mice (8–22 weeks) were snap‐frozen, crushed using SK‐Mill (SK‐100, FUNAKOSHI), and dissolved in a buffer composed of 9M Urea, 2% SDS, 2% TritonX‐100, 1% dithiothreitol, and 10 mM Tris‐HCl, pH 6.8), containing Protease Inhibitor Cocktail (Sigma‐Aldrich).…”

“…Echocardiographic examinations were performed using a Vevo 2100 (Visual Sonics) as described previously (Ushijima et al, ). Briefly, under anesthesia with 1–2% isoflurane inhalation, two‐dimensional targeted M‐mode images were obtained from the short‐axis view at the level of papillary muscles.…”

Exome sequencing identifies a FHOD3 p.S527del mutation in a Chinese family with hypertrophic cardiomyopathy

“…FHOD3, a member of the diaphanous‐related formins (DRF), is implicated in the regulation of actin assembly in cardiomyocytes and in sarcomere organisation during myofibrillogenesis . Studies in FHOD3 ‐knockout mice established that FHOD3 plays a role in the maintenance of normal cardiac function of the perinatal and adult heart . In 2018, Ochoa et al first reported that FHOD3 was considered a novel genetic cause of HCM in a large scale European population study.…”