Elena A. Matveeva

Mitochondrial membrane potential is regulated by vimentin intermediate filaments

This study demonstrates that the association of mitochondria with vimentin intermediate filaments (VIFs) measurably increases their membrane potential. This increase is detected by quantitatively comparing the fluorescence intensity of mitochondria stained with the membrane potential‐sensitive dye tetramethylrhodamine‐ethyl ester (TMRE) in murine vimentin‐null fibroblasts with that in the same cells expressing human vimentin (~35% rise). When vimentin expression is silenced by small hairpin RNA (shRNA) to reduce vimentin by 90%, the fluorescence intensity of mitochondria decreases by 20%. The increase in membrane potential is caused by specific interactions between a subdomain of the non‐α‐helical N terminus (residues 40 to 93) of vimentin and mitochondria. In rho 0 cells lacking mitochondrial DNA (mtDNA) and consequently missing several key proteins in the mitochondrial respiratory chain (ρ0 cells), the membrane potential generated by an alternative anaerobic process is insensitive to the interactions between mitochondria and VIF. The results of our studies show that the close association between mitochondria and VIF is important both for determining their position in cells and their physiologic activity.—Chernoivanenko, I. S., Matveeva, E. A., Gelfand, V. I., Goldman, R. D., Minin, A. A., Mitochondrial membrane potential is regulated by vimentin intermediate filaments. FASEB J. 29, 820–827 (2015). www.fasebj.org

Vimentin is involved in regulation of mitochondrial motility and membrane potential by Rac1

ABSTRACT In this study we show that binding of mitochondria to vimentin intermediate filaments (VIF) is regulated by GTPase Rac1. The activation of Rac1 leads to a redoubling of mitochondrial motility in murine fibroblasts. Using double-mutants Rac1(G12V, F37L) and Rac1(G12V, Y40H) that are capable to activate different effectors of Rac1, we show that mitochondrial movements are regulated through PAK1 kinase. The involvement of PAK1 kinase is also confirmed by the fact that expression of its auto inhibitory domain (PID) blocks the effect of activated Rac1 on mitochondrial motility. The observed effect of Rac1 and PAK1 kinase on mitochondria depends on phosphorylation of the Ser-55 of vimentin. Besides the effect on motility Rac1 activation also decreases the mitochondrial membrane potential (MMP) which is detected by ∼20% drop of the fluorescence intensity of mitochondria stained with the potential sensitive dye TMRM. One of important consequences of the discovered regulation of MMP by Rac1 and PAK1 is a spatial differentiation of mitochondria in polarized fibroblasts: at the front of the cell they are less energized (by ∼25%) than at the rear part.

Vimentin intermediate filaments protect mitochondria from oxidative stress

The role of intermediate filaments (IFs) in eukaryotic cells is still unclear. The disturbance of mitochondria distribution and function, in particular the enhanced production of reactive oxygen species (ROS) and decreased membrane potential, is observed in cells devoid of IFs. The aim of this work was to study the dependence of mitochondria sensitivity to oxidative stress on the presence of vimentin IFs. It was found that mitochondria are less sensitive to ROS in cells containing vimentin than in cells devoid of vimentin. Besides, mitochondrial membrane potential was demonstrated to increase upon regeneration of vimentin IFs in the cells. Substitution of Pro-57 by Arg in N-terminal part of the vimentin molecule abandoned its protective ability and the effect on mitochondrial membrane potential.

Vimentin intermediate filaments increase mitochondrial membrane potential

Mitochondria are the main source of energy in eukaryotic cells. They also play an important role in the number of other processes, such as regulation of calcium concentration and sequestration of apoptotic factors. Almost all functions of mitochondria depend on their ability to generate and maintain membrane potential by means of aerobic respiration. The level of mitochondrial potential is under the control of different inner and outer factors. However, mechanisms of this regulation are still poorly understood. In the present study we answer the question of how membrane potential of mitochondria depends on their motility. Using the potential-dependent dye MitoTracker Red, fluorescent microscopy of live cells, and the analysis of mitochondrial motility, two sub-populations of mitochondria were determined: (1) moving mitochondria transported along microtubules and (2) stationary mitochondria. We have shown that stationary mitochondria have higher membrane potential than moving mitochondria. It was also found that the level of potential of mitochondria is regulated by their interaction with vimentin intermediate filaments.

One-Pot Chlorine-Free Synthesis of Chiral Organophosphorus Compounds from Elemental Phosphorus and α-Methylstyrene Dimer

Direct phosphorylation of α-methylstyrene dimer with red phosphorus in KOH/DMSO superbasic system has provided the preparation of 4-methyl-2,4-diphenylpentylphosphonous acid (heating at 105°C for 3 h) or tris(4-methyl-2,4-diphenylpentyl)phosphine oxide (microwave irradiation, 15 min) in 21 and 38% yield, respectively.

Reaction of 9-bromoanthracene with red phosphorus in the system KOH‒DMSO

Phosphorylation of anthracenes and their halogen derivatives is usually accomplished with the aid of phosphorus halides [5–7, 12, 18, 19], alkyl and aryl phosphites [3, 17, 20–22], or hypophosphites [23]. For example, anthracen-9-ylphosphinic acid was synthesized in two steps including reaction of phosphorus trihalide with anthrylmagnesium halide and subsequent hydrolysis of anthryl(dihalo)phosphine [1]. Kalek and Stawinski [23] described microwave-assisted synthesis of anthracen-9-ylphosphinic acid from 9-bromoanthracene and anilinium phosphinite in the presence of Pd2(dba)2 · CHCl3‒Xantphos‒Et3N as catalytic system. One of the most convenient methods for the formation of P–C bond and synthesis of organophosphorus compounds is based on the direct reaction of elemental phosphorus with electrophiles in the presence of strong bases [24–31]. Herein, we report for the first time phosphorylation of 9-bromoanthracene (1) with red phosphorus. By heating (40‒60°C, 3 h) bromide 1 with red phosphorus in the system KOH‒DMSO containing a small amount of water we obtained anthracen-9ylphosphinic acid (2) in up to 10% yield (unoptimized). Under these conditions, 30% of anthracene 3 and 20% of 9,10-dihydroanthracene (4) were also formed (Scheme 1). The reaction mixture also contained traces of anthracen-9-ol (according to the GC/MS data). No phosphorylation of 1 was observed in the absence of base, which confirms nucleophilic character of the C‒P bond formation. In the first step, elemental phosphorus in superbasic medium generates phosphorus-containing nucleophilic species, polyphosphide (A) and polyphosphinite ions (B) [25, 26], which then react with bromide 1 to give acid 2 (Scheme 2). Polyphosphide ions are most likely to be involved in concurrent one-electron transfer process with formation of unstable radical anion C which decomposes into bromide ion and anthryl radical D. The latter is capable of abstracting hydrogen from DMSO, yielding neutral anthracene (3). The subsequent electron transfer to molecule 3 from anion A or radical anion C leads to the formation of the reduction product, 9,10-dihydroanthracene (4) (Scheme 3). This mechanism is consistent with published data for reactions of 9-bromoanthracene with sulfur and ISSN 1070-4280, Russian Journal of Organic Chemistry, 2016, Vol. 52, No. 7, pp. 1059–1061.