**9. Conclusions**

Many structural and functional interactions were found to be involved in the integration of mitochondria with other cellular systems like the SR and cytoskeleton, connecting mitochondrial function, dynamics, and regulation with the entire cell physiology, in particular in the most energy consuming organ, the heart. Overall, existing studies provide strong evidence that cytoskeletal proteins such as tubulin beta-II and plectin 1b interact with mitochondria. The interaction regulates metabolic fluxes via the energy transferring supercomplex VDAC-MitCK-ANT which, in turn, coordinates mitochondrial respiration and OXPHOS and the entire cellular physiology. The detailed characterization of molecular mechanisms implicated in mitochondrial–cytoskeleton interactions under normal and pathological conditions can be helpful for the development of new therapeutic approaches.

It should be pointed out that many structural and functional aspects of mitochondria–cytoskeletal proteins interactions, as well as detailed molecular mechanisms of their formation, are not ye<sup>t</sup> known, and the interactions of tubulin beta-II or plectin 1b with mitochondria (mitochondrial VDAC) have to be shown more directly, using the most modern methodologies, for example, by using: (i) imaging approaches with a higher levels of spatial and temporal resolutions, (ii) application of mitochondrial green fluorescent proteins (GFPs) specifically targeted to mitochondria, (iii) use of fluorescence resonance energy transfer (FRET) method to directly analyze possible protein-protein interactions and proximities, (iv) reconstruction or reconstitution experiments using tubulin β-II transfection and specific fragments of plectin, and (v) advancement of recombinant α- and β-tubulin isoforms with modifications of the C-terminal tail.

**Author Contributions:** Conceptualization, A.V.K., M.J.A. and S.J.; validation, S.J., M.J.A. and R.M.; resources, M.G. and R.M.; data curation, S.J. and M.G.; writing—original draft preparation, A.V.K. and S.J.; writing—review and editing, A.V.K., J.H. and S.J.; supervision, M.J.A., M.G. and R.M.; project administration, M.J.A., M.G. and R.M.; funding acquisition, J.H. and M.J.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by MFF-Tirol (Project 291), "Tiroler Wissenschaftsförderung", the Austrian Science Fund (FWF Project I3089-B28), the "Tirol-Kliniken GmbH", and the National Institute of General Medical Sciences of the National Institutes of Health (NIH Grant SC1GM128210 to S.J.).

**Conflicts of Interest:** The authors declare no conflict of interest.
