ANALYSIS OF NUCLEAR MORPHOLOGY OF DESMIN KNOCK-OUT MYOBLASTS

Abstract

Desminopathies are degenerative muscle diseases caused by mutations of the desmin gene. Desmin is an intermediate filament protein that is mainly expressed in smooth muscles, skeletal muscles and cardiac muscles cells. There it connects the nuclei, mitochondria, myofibrils, and the sarcolemma, thus providing the structure within the cells. Mutations of the desmin gene lead to autosomal-dominant, autosomal recessive and sporadic myopathies and/or cardiomyopathies (Clemen, Herrmann et al. 2013). Recessive forms of the disease include the complete absence of desmin (Henderson, De Waele et al. 2013, Ruppert, Heckmann et al. 2020). To investigate this form of the disease in more detail, desmin knockout mice were already bred. This study is mainly concerned with the nuclear morphology of the myoblasts (muscle precursor cells), of the mice mentioned above. In cardiomyocytes it has already been observed that a knock-down of desmin led to misfolded nuclei (Heffler, Shah et al. 2020). To investigate the issue in skeletal muscle derived cells, murine wild-type myoblasts were compared with homozygous desmin knock-out myoblasts. First, it was determined whether the newly generated myoblast cells lines are suitable for further experiments by testing their growth and differentiation ability. Afterwards, several immunofluorescence stainings were performed, which stained the inner or outer nuclear envelope or the nuclear lamina. In addition, the myoblasts were exposed to lower oxygen conditions to observe oxygendependent changes of the nuclear morphology. The immunofluorescence images of the homozygous desmin knock-out myoblasts also showed crumpled or folded nuclei, and also a significant decrease in nuclear size. When the myoblasts were exposed to an oxygen concentration of 1%, fewer nuclear abnormalities were observed in homozygous cells, while the number of abnormalities in wild-type cells remained unchanged. Moreover, the nuclei of myoblasts exposed to 1 % were significantly larger in both wild-type and homozygous desmin knock-out myoblasts as compared to 21% oxygen. Since Desmin is connected to the nuclear envelope via components of the LINC complex, these findings may indicate that desmin has a traction function that supports the nucleus in its oval or round shape (Heffler, Shah et al. 2020). Furthermore, a comparison of wild-type and desmin knock-out nuclei of cultured myoblasts and mature muscle tissue revealed similarly smaller nuclei, which verifies the myoblasts cell lines as valuable model system.