Desmin intermediate filaments (IFs) play an important role in maintaining the structural and functional integrity of muscle cells. They connect contractile myofibrils to plasma membrane, nuclei, and mitochondria. Disturbance of their network due to desmin mutations or deficiency leads to an infringement of myofibril organization and to a deterioration of mitochondrial distribution, morphology, and functions. The nature of the interaction of desmin IFs with mitochondria is not clear. To elucidate the possibility that desmin can directly bind to mitochondria, we have undertaken the study of their interaction in vitro. Using desmin mutant Des(Y122L) that forms unit-length filaments (ULFs) but is incapable of forming long filaments and, therefore, could be effectively separated from mitochondria by centrifugation through sucrose gradient, we probed the interaction of recombinant human desmin with mitochondria isolated from rat liver. Our data show that desmin can directly bind to mitochondria, and this binding depends on its N-terminal domain. We have found that mitochondrial cysteine protease can disrupt this interaction by cleavage of desmin at its N-terminus.

The formation of specific cellular protrusions, plasma membrane blebs, underlies the amoeboid mode of cell motility, which is characteristic for free-living amoebae and leukocytes, and can also be adopted by stem and tumor cells to bypass unfavorable migration conditions and thus facilitate their long-distance migration. Not all cells are equally prone to bleb formation. We have previously shown that membrane blebbing can be experimentally induced in a subset of HT1080 fibrosarcoma cells, whereas other cells in the same culture under the same conditions retain non-blebbing mesenchymal morphology. Here we show that this heterogeneity is associated with the distribution of vimentin intermediate filaments (VIFs). Using different approaches to alter the VIF organization, we show that blebbing activity is biased toward cell edges lacking abundant VIFs, whereas the VIF-rich regions of the cell periphery exhibit low blebbing activity. This pattern is observed both in interphase fibroblasts, with and without experimentally induced blebbing, and during mitosis-associated blebbing. Moreover, the downregulation of vimentin expression or displacement of VIFs away from the cell periphery promotes blebbing even in cells resistant to bleb-inducing treatments. Thus, we reveal a new important function of VIFs in cell physiology that involves the regulation of non-apoptotic blebbing essential for amoeboid cell migration and mitosis.

Neural precursor cells contain two types of intermediate filaments (IFs): neurofilaments consisting of three IV type proteins and vimentin belonging to the type III IF proteins that disappear at the later stages of differentiation. The involvement of vimentin in neurogenesis was demonstrated earlier; however, the role of its temporary expression in neurons is not clear. We showed that the vimentin IFs that interacted with mitochondria maintained their membrane potential at the appropriate level, and thus, ensured their proper function. We examined the dependence of the mitochondrial membrane potential on the expression of vimentin in a CAD catecholaminergic neuronal cell line that was actively dividing in full culture media but stopped growing and started developing neurites when the serum was removed. Using the CRISPR Cas9 system to knock out the vimentin gene in these cells, we investigated the impact of this on the mitochondrial membrane potential. Our data show that the deletion of the vimentin IFs led to a decrease in the level of the mitochondrial potential. When the vimentin network in these cells was reconstituted by transfection with a plasmid that encoded human protein, the level of the potential was restored. Interestingly, mutated vimentin with a disrupted mitochondria-binding site had no such effect. Our data point to vimentin as a possible target in some neurological pathologies.

Neural precursor cells contain two types of intermediate filaments (IFs): neurofilaments consisting of three IV type proteins, and vimentin belonging to the III type of IF proteins that disappears on the later stages of differentiation. The involvement of vimentin in neurogenesis was demonstrated earlier, however the role of its temporary expression in neurons is not clear. We have shown that vimentin IFs interacting with mitochondria maintain their membrane potential on the appropriate level and thus ensure their proper function. We examined the dependence of mitochondrial membrane potential on the expression of vimentin in CAD catecholaminergic neuronal cell line that is actively dividing in the full culture media but stop growing and start developing neurites when serum is removed. Using CRIPR Cas9 system to knockout the vimentin gene in these cells we investigated the impact of this on the mitochondrial membrane potential. Our data show that deletion of vimentin IFs leads to decrease of the level of mitochondrial potential. When the vimentin network in these cells was reconstituted by transfection with plasmid encoding human protein the level of potential restored. Interestingly, mutated vimentin with disrupted mitochondria-binding site had no such an effect. Our data point to vimentin as a possible target in some neurological pathologies.