Mitochondrial ROS Signaling in Organismal Homeostasis

Generation, transformation, and utilization of organic molecules in support of cellular differentiation, growth, and maintenance are basic tenets that define life. In eukaryotes, mitochondrial oxygen consumption plays a central role in these processes. During the process of oxidative phosphorylation, mitochondria utilize oxygen to generate ATP from organic fuel molecules but in the process also produce reactive oxygen species (ROS). While ROS have long been appreciated for their damage-promoting, detrimental effects, there is now a greater understanding of their roles as signaling molecules. Here, we review mitochondrial ROS-mediated signaling pathways with an emphasis on how they are involved in various basal and adaptive physiological responses that control organismal homeostasis

A text message intervention for quitting cigarette smoking among young adults experiencing homelessness: study protocol for a pilot randomized controlled trial.

BackgroundCigarette smoking is much more prevalent among young people experiencing homelessness than in the general population of adolescents and young adults. Although many young homeless smokers are motivated to quit, there are no empirically-evaluated smoking cessation programs for this population. It is important that any such program address the factors known to be associated with quitting-related outcomes among homeless young people, to provide ongoing support in a way that accommodates the mobility of this population, and does not rely on scarce service provider resources for its delivery. The objective of this project is to develop and pilot test a text messaging-based intervention (TMI), as an adjunct to brief cessation counseling and provision of nicotine patches, to help homeless young people who want to quit smoking.Methods/designThis pilot study will utilize a cluster cross-over randomized controlled design with up to 80 current smokers who desire to quit and are recruited from three drop-in centers serving young people experiencing homelessness in the Los Angeles area. All participants will be provided with a minimum standard of care: a 30-min group-based smoking cessation counseling session and free nicotine replacement. Half of these smokers will then also receive the TMI, as an adjunct to this standard care, which will provide 6 weeks of ongoing support for quitting. This support includes continued and more intensive education regarding nicotine dependence, quitting smoking, and relapse; does not require additional agency resources; can be available "on demand" to users; and includes features to personalize the quitting experience. This study will investigate whether receiving the TMI adjunct to standard smoking cessation care results in greater reductions in cigarette smoking compared to standard care alone over a 3-month period.DiscussionThis study has the potential to address an important gap in the clinical research literature on cigarette smoking cessation and provide empirical support for using a TMI to provide ongoing assistance and support for quitting among young smokers experiencing homelessness. Trial registration ClinicalTrials.gov Identifier NCT03874585. Registered March 14, 2019, https://clinicaltrials.gov/ct2/show/record/NCT03874585

Stria Vascularis Dysfunction in a Mouse Model of Mitochondrial Hearing Loss

We recently described a transgenic mouse model of hearing loss induced by over-expression of the mitochondrial ribosomal RNA (rRNA) methyltransferase, TFB1M (Tg-TFB1M). These mice recapitulate maternally inherited deafness caused by the human A1555G mtDNA mutation, which results in increased methylation of the 12S rRNA in mitochondrial ribosomes and tissue-specific susceptibility to apoptosis. The present study aims to identify the specific cellular and tissue based pathologies underlying this form of deafness

Mitochondrial Stress Engages E2F1 Apoptotic Signaling to Cause Deafness

SummaryMitochondrial dysfunction causes poorly understood tissue-specific pathology stemming from primary defects in respiration, coupled with altered reactive oxygen species (ROS), metabolic signaling, and apoptosis. The A1555G mtDNA mutation that causes maternally inherited deafness disrupts mitochondrial ribosome function, in part, via increased methylation of the mitochondrial 12S rRNA by the methyltransferase mtTFB1. In patient-derived A1555G cells, we show that 12S rRNA hypermethylation causes ROS-dependent activation of AMP kinase and the proapoptotic nuclear transcription factor E2F1. This retrograde mitochondrial-stress relay is operative in vivo, as transgenic-mtTFB1 mice exhibit enhanced 12S rRNA methylation in multiple tissues, increased E2F1 and apoptosis in the stria vascularis and spiral ganglion neurons of the inner ear, and progressive E2F1-dependent hearing loss. This mouse mitochondrial disease model provides a robust platform for deciphering the complex tissue specificity of human mitochondrial-based disorders, as well as the precise pathogenic mechanism of maternally inherited deafness and its exacerbation by environmental factors.PaperFlic

Prohibitin-1 maintains the angiogenic capacity of endothelial cells by regulating mitochondrial function and senescence

Prohibitin 1 (PHB1) is a highly conserved protein that is mainly localized to the inner mitochondrial membrane and has been implicated in regulating mitochondrial function in yeast. Because mitochondria are emerging as an important regulator of vascular homeostasis, we examined PHB1 function in endothelial cells. PHB1 is highly expressed in the vascular system and knockdown of PHB1 in endothelial cells increases mitochondrial production of reactive oxygen species via inhibition of complex I, which results in cellular senescence. As a direct consequence, both Akt and Rac1 are hyperactivated, leading to cytoskeletal rearrangements and decreased endothelial cell motility, e.g., migration and tube formation. This is also reflected in an in vivo angiogenesis assay, where silencing of PHB1 blocks the formation of functional blood vessels. Collectively, our results provide evidence that PHB1 is important for mitochondrial function and prevents reactive oxygen species–induced senescence and thereby maintains the angiogenic capacity of endothelial cells

Paradoxical aortic stiffening and subsequent cardiac dysfunction in Hutchinson-Gilford progeria syndrome

[EN] Hutchinson-Gilford progeria syndrome (HGPS) is an ultra-rare disorder with devastating sequelae resulting in early death, presently thought to stem primarily from cardiovascular events. We analyse novel longitudinal cardiovascular data from a mouse model of HGPS (Lmna(G609G/G609G)) using allometric scaling, biomechanical phenotyping, and advanced computational modelling and show that late-stage diastolic dysfunction, with preserved systolic function, emerges with an increase in the pulse wave velocity and an associated loss of aortic function, independent of sex. Specifically, there is a dramatic late-stage loss of smooth muscle function and cells and an excessive accumulation of proteoglycans along the aorta, which result in a loss of biomechanical function (contractility and elastic energy storage) and a marked structural stiffening despite a distinctly low intrinsic material stiffness that is consistent with the lack of functional lamin A. Importantly, the vascular function appears to arise normally from the low-stress environment of development, only to succumb progressively to pressure-related effects of the lamin A mutation and become extreme in the peri-morbid period. Because the dramatic life-threatening aortic phenotype manifests during the last third of life there may be a therapeutic window in maturity that could alleviate concerns with therapies administered during early periods of arterial development.This work was supported, in part, by grants from the US National Institutes of Health: R01 HL105297 (J.D.H.) and P01 HL134605 (Dan Rifkin) and R01 AG047632 and R33 ES025636 (G.S.S.)Murtada, SI.; Kawamura, Y.; Caulk, AW.; Ahmadzadeh, H.; Mikush, N.; Zimmerman, K.; Kavanagh, D.... (2020). Paradoxical aortic stiffening and subsequent cardiac dysfunction in Hutchinson-Gilford progeria syndrome. Journal of The Royal Society Interface. 17(166):1-12. https://doi.org/10.1098/rsif.2020.00661121716

Transcriptional activation by mitochondrial transcription factor A involves preferential distortion of promoter DNA

Mitochondrial transcription factor A (mtTFA/TFAM) is a nucleus-encoded, high-mobility-group-box (HMG-box) protein that regulates transcription of the mitochondrial genome by specifically recognizing light-strand and heavy-strand promoters (LSP, HSP1). TFAM also binds mitochondrial DNA in a non-sequence specific (NSS) fashion and facilitates its packaging into nucleoid structures. However, the requirement and contribution of DNA-bending for these two different binding modes has not been addressed in detail, which prompted this comparison of binding and bending properties of TFAM on promoter and non-promoter DNA. Promoter DNA increased the stability of TFAM to a greater degree than non-promoter DNA. However, the thermodynamic properties of DNA binding for TFAM with promoter and non-specific (NS) DNA were similar to each other and to other NSS HMG-box proteins. Fluorescence resonance energy transfer assays showed that TFAM bends promoter DNA to a greater degree than NS DNA. In contrast, TFAM lacking the C-terminal tail distorted both promoter and non-promoter DNA to a significantly reduced degree, corresponding with markedly decreased transcriptional activation capacity at LSP and HSP1 in vitro. Thus, the enhanced bending of promoter DNA imparted by the C-terminal tail is a critical component of the ability of TFAM to activate promoter-specific initiation by the core mitochondrial transcription machinery

Structural analysis and DNA binding of the HMG domains of the human mitochondrial transcription factor A

The mitochondrial transcription factor A (mtTFA) is central to assembly and initiation of the mitochondrial transcription complex. Human mtTFA (h-mtTFA) is a dual high mobility group box (HMGB) protein that binds site-specifically to the mitochondrial genome and demarcates the promoters for recruitment of h-mtTFB1, h-mtTFB2 and the mitochondrial RNA polymerase. The stoichiometry of h-mtTFA was found to be a monomer in the absence of DNA, whereas it formed a dimer in the complex with the light strand promoter (LSP) DNA. Each of the HMG boxes and the C-terminal tail were evaluated for their ability to bind to the LSP DNA. Removal of the C-terminal tail only slightly decreased nonsequence specific DNA binding, and box A, but not box B, was capable of binding to the LSP DNA. The X-ray crystal structure of h-mtTFA box B, at 1.35 Å resolution, revealed the features of a noncanonical HMG box. Interactions of box B with other regions of h-mtTFA were observed. Together, these results provide an explanation for the unusual DNA-binding properties of box B and suggest possible roles for this domain in transcription complex assembly