Mitochondrial morphology governs ATP production rate.

Life is based on energy conversion. In particular, in the nervous system, significant amounts of energy are needed to maintain synaptic transmission and homeostasis. To a large extent, neurons depend on oxidative phosphorylation in mitochondria to meet their high energy demand. For a comprehensive understanding of the metabolic demands in neuronal signaling, accurate models of ATP production in mitochondria are required. Here, we present a thermodynamically consistent model of ATP production in mitochondria based on previous work. The significant improvement of the model is that the reaction rate constants are set such that detailed balance is satisfied. Moreover, using thermodynamic considerations, the dependence of the reaction rate constants on membrane potential, pH, and substrate concentrations are explicitly provided. These constraints assure that the model is physically plausible. Furthermore, we explore different parameter regimes to understand in which conditions ATP production or its export are the limiting steps in making ATP available in the cytosol. The outcomes reveal that, under the conditions used in our simulations, ATP production is the limiting step and not its export. Finally, we performed spatial simulations with nine 3-D realistic mitochondrial reconstructions and linked the ATP production rate in the cytosol with morphological features of the organelles.

H2S contributed from CSE during cellular senescence suppresses inflammation and nitrosative stress.

Aging involves the time-dependent deterioration of physiological functions attributed to various intracellular and extracellular factors. Cellular senescence is akin to aging and involves alteration in redox homeostasis. This is primarily marked by increased reactive oxygen/nitrogen species (ROS/RNS), inflammatory gene expression, and senescence-associated beta-galactosidase activity, all hallmarks of aging. It is proposed that gasotransmitters which include hydrogen sulfide (H2S), carbon monoxide (CO), and nitric oxide (NO), may affect redox homeostasis during senescence. H2S has been independently shown to induce DNA damage and suppress oxidative stress. While an increase in NO levels during aging is well established, the role of H2S has remained controversial. To understand the role of H2S during aging, we evaluated H2S homeostasis in non-senescent and senescent cells, using a combination of direct measurements with a fluorescent reporter dye (WSP-5) and protein sulfhydration analysis. The free intracellular H2S and total protein sulfhydration levels are high during senescence, concomitant to cystathionine gamma-lyase (CSE) expression induction. Using lentiviral shRNA-mediated expression knockdown, we identified that H2S contributed by CSE alters global gene expression, which regulates key inflammatory processes during cellular senescence. We propose that H2S decreases inflammation during cellular senescence by reducing phosphorylation of IκBα and the p65 subunit of nuclear factor kappa B (NF-κB). H2S was also found to reduce NO levels, a significant source of nitrosative stress during cellular senescence. Overall, we establish H2S as a key gasotransmitter molecule that regulates inflammatory phenotype and nitrosative stress during cellular senescence.

Leveraging an enzyme/artificial substrate system to enhance cellular persulfides and mitigate neuroinflammation.

Persulfides and polysulfides, collectively known as the sulfane sulfur pool along with hydrogen sulfide (H2S), play a central role in cellular physiology and disease. Exogenously enhancing these species in cells is an emerging therapeutic paradigm for mitigating oxidative stress and inflammation that are associated with several diseases. In this study, we present a unique approach of using the cell's own enzyme machinery coupled with an array of artificial substrates to enhance the cellular sulfane sulfur pool. We report the synthesis and validation of artificial/unnatural substrates specific for 3-mercaptopyruvate sulfurtransferase (3-MST), an important enzyme that contributes to sulfur trafficking in cells. We demonstrate that these artificial substrates generate persulfides in vitro as well as mediate sulfur transfer to low molecular weight thiols and to cysteine-containing proteins. A nearly 100-fold difference in the rates of H2S production for the various substrates is observed supporting the tunability of persulfide generation by the 3-MST enzyme/artificial substrate system. Next, we show that the substrate 1a permeates cells and is selectively turned over by 3-MST to generate 3-MST-persulfide, which protects against reactive oxygen species-induced lethality. Lastly, in a mouse model, 1a is found to significantly mitigate neuroinflammation in the brain tissue. Together, the approach that we have developed allows for the on-demand generation of persulfides in vitro and in vivo using a range of shelf-stable, artificial substrates of 3-MST, while opening up possibilities of harnessing these molecules for therapeutic applications.

Integrating deep learning CT-scan model, biological and clinical variables to predict severity of COVID-19 patients.

The SARS-COV-2 pandemic has put pressure on intensive care units, so that identifying predictors of disease severity is a priority. We collect 58 clinical and biological variables, and chest CT scan data, from 1003 coronavirus-infected patients from two French hospitals. We train a deep learning model based on CT scans to predict severity. We then construct the multimodal AI-severity score that includes 5 clinical and biological variables (age, sex, oxygenation, urea, platelet) in addition to the deep learning model. We show that neural network analysis of CT-scans brings unique prognosis information, although it is correlated with other markers of severity (oxygenation, LDH, and CRP) explaining the measurable but limited 0.03 increase of AUC obtained when adding CT-scan information to clinical variables. Here, we show that when comparing AI-severity with 11 existing severity scores, we find significantly improved prognosis performance; AI-severity can therefore rapidly become a reference scoring approach.

A matrix targeted fluorescent probe to monitor mitochondrial dynamics.

Mitochondria are an indispensable organelle for energy production and regulation of cellular metabolism. The structural and functional alterations to mitochondria instigate pathological conditions of cancer, and aging-associated and neurodegenerative disorders. The normal functioning of mitochondria is maintained by quality control mechanisms involving dynamic fission, fusion, biogenesis and mitophagy. Under conditions of mitophagy and neurodegenerative diseases, mitochondria are exposed to different acidic environments and high levels of reactive oxygen species (ROS). Therefore stable molecular tools and methods are required to monitor the pathways linked to mitochondrial dysfunction and disease conditions. Herein, we report a far-red fluorescent probe (Mito-TG) with excellent biocompatibility, biostability, photostability, chemical stability and turn on emission for selective targeting of the mitochondrial matrix in different live cells. The probe was successfully employed for monitoring dynamic processes of mitophagy and amyloid beta (Aß) induced mitochondrial structural changes.

Carbonyl Sulfide (COS) Donor Induced Protein Persulfidation Protects against Oxidative Stress.

The emergence of hydrogen sulfide (H2 S) as an important signalling molecule in redox biology with therapeutic potential has triggered interest in generating this molecule within cells. One strategy that has been proposed is to use carbonyl sulfide (COS) as a surrogate for hydrogen sulfide. Small molecules that generate COS have been shown to produce hydrogen sulfide in the presence of carbonic anhydrase, a widely prevalent enzyme. However, other studies have indicated that COS may have biological effects which are distinct from H2 S. Thus, it would be useful to develop tools to compare (and contrast) effects of COS and H2 S. Here we report enzyme-activated COS donors that are capable of inducing protein persulfidation, which is symptomatic of generation of hydrogen sulfide. The COS donors are also capable of mitigating stress induced by elevated reactive oxygen species. Together, our data suggests that the effects of COS parallel that of hydrogen sulfide, laying the foundation for further development of these donors as possible therapeutic agents.

Visible-Light-Triggered Uncaging of Carbonyl Sulfide for Hydrogen Sulfide (H2S) Release.

Generation of hydrogen sulfide (H2S) is challenging and few methods are capable of localized delivery of this gas. Here, a boron dipyrromethene-based carbamothioate (BDP-H2S) that is uncaged by visible light of 470 nm to generate carbonyl sulfide (COS), which is rapidly hydrolyzed to H2S in the presence of carbonic anhydrase, a widely prevalent enzyme, is reported.