Matrix stiffening promotes perinuclear clustering of mitochondria.

Mechanical cues from the tissue microenvironment, such as the stiffness of the extracellular matrix, modulate cellular forms and functions. As numerous studies have shown, this modulation depends on the stiffness-dependent remodeling of cytoskeletal elements. In contrast, very little is known about how the intracellular organelles such as mitochondria respond to matrix stiffness and whether their form, function, and localization change accordingly. Here, we performed an extensive quantitative characterization of mitochondrial morphology, subcellular localization, dynamics, and membrane tension on soft and stiff matrices. This characterization revealed that while matrix stiffness affected all these aspects, matrix stiffening most distinctively led to an increased perinuclear clustering of mitochondria. Subsequently, we could identify the matrix stiffness-sensitive perinuclear localization of filamin as the key factor dictating this perinuclear clustering. The perinuclear and peripheral mitochondrial populations differed in their motility on soft matrix but surprisingly they did not show any difference on stiff matrix. Finally, perinuclear mitochondrial clustering appeared to be crucial for the nuclear localization of RUNX2 and hence for priming human mesenchymal stem cells towards osteogenesis on a stiff matrix. Taken together, we elucidate a dependence of mitochondrial localization on matrix stiffness, which possibly enables a cell to adapt to its microenvironment. [Media: see text] [Media: see text] [Media: see text] [Media: see text].

Organelle morphology and positioning orchestrate physiological and disease-associated processes.

In cells, organelles are distributed nonrandomly to regulate cells' physiological and disease-associated processes. Based on their morphology, position within the cell, and contacts with other organelles, they exert different biological functions. Endo-lysosomes are critical cell metabolism and nutrient-sensing regulators modulating cell growth and cellular adaptation in response to nutrient availability. Their spatial distribution is intimately linked to their function. In this review, we will discuss the role of endolysosomes under physiological conditions and in the context of cancer progression, with a special focus on their morphology, the molecular mechanisms determining their subcellular position, and the contacts they form with other organelles. We aim to highlight the relationship between cell architecture and cell function and its impact on maintaining organismal homeostasis.

Mechanical imbalance between normal and cancer cells drives epithelial defense against cancer.

Cell competition enables normal wildtype cells of epithelial tissue to eliminate mutant cells expressing activated oncoproteins such as HRasV12. However, the driving force behind this fundamental epithelial defense against cancer remains enigmatic. Here, we employ tissue stress microscopy and theoretical modeling and invent a new collective compressibility measurement technique called gel compression microscopy to unveil the mechanism governing cell competition. Stress microscopy reveals unique compressive stress experienced by the mutant cells, contrasting with predominantly tensile stress experienced by normal cells. A cell-based computer simulation then predicts that this compressive stress arises out of a mechanical imbalance between two competing populations due to a difference in their collective compressibility and rigidity. Gel compression microscopy empirically confirms the prediction and elucidates a three-fold higher compressibility of the mutant population than the normal population. Mechanistically, this difference stems from the reduced abundance and coupling of junctional E-cadherin molecules in the mutant cells, which weakens cell-cell adhesions and renders the mutant population more compressible. Taken together, our study elucidates both the physical principle and the underlying molecular mechanism driving cell competition in epithelial defense against cancer and opens new directions for mechanomedicine in cancer.

Collective heterogeneity of mitochondrial potential in contact inhibition of proliferation.

In the epithelium, cell density and cell proliferation are closely connected to each other through contact inhibition of proliferation (CIP). Depending on cell density, CIP proceeds through three distinct stages: the free-growing stage at low density, the pre-epithelial transition stage at medium density, and the post-epithelial transition stage at high density. Previous studies have elucidated how cell morphology, motion, and mechanics vary in these stages. However, it remains unknown whether cellular metabolism also has a density-dependent behavior. By measuring the mitochondrial membrane potential at different cell densities, here we reveal a heterogeneous landscape of metabolism in the epithelium, which appears qualitatively distinct in three stages of CIP and did not follow the trend of other CIP-associated parameters, which increases or decreases monotonically with increasing cell density. Importantly, epithelial cells established a collective metabolic heterogeneity exclusively in the pre-epithelial transition stage, where the multicellular clusters of high- and low-potential cells emerged. However, in the post-epithelial transition stage, the metabolic potential field became relatively homogeneous. Next, to study the underlying dynamics, we constructed a system biology model, which predicted the role of cell proliferation in metabolic potential toward establishing collective heterogeneity. Further experiments indeed revealed that the metabolic pattern spatially correlated with the proliferation capacity of cells, as measured by the nuclear localization of a pro-proliferation protein, YAP. Finally, experiments perturbing the actomyosin contractility revealed that, while metabolic heterogeneity was maintained in the absence of actomyosin contractility, its ab initio emergence depended on the latter. Taken together, our results revealed a density-dependent collective heterogeneity in the metabolic field of a pre-epithelial transition-stage epithelial monolayer, which may have significant implications for epithelial form and function.

Catalyst-Free Transfer Hydrogenation of Activated Alkenes Exploiting Isopropanol as the Sole and Traceless Reductant.

Both metal-catalyzed and organocatalytic transfer hydrogenation reactions are widely employed for the reduction of C=O and C=N bonds. However, selective transfer hydrogenation reactions of C=C bonds remain challenging. Therefore, the chemoselective transfer hydrogenation of olefins under mild conditions and in the absence of metal catalysts, using readily available and inexpensive reducing agents (i.e. primary and secondary alcohols), will mark a significant advancement towards the development of green transfer hydrogenation strategies. Described herein is an unconventional catalyst-free transfer hydrogenation reaction of activated alkenes using isopropanol as an eco-friendly reductant and solvent. The reaction gives convenient synthetic access to a wide range of substituted malonic acid half oxyesters (SMAHOs) in moderate to good yields. Mechanistic investigations point towards an unprecedented hydrogen bond-assisted transfer hydrogenation process.

Correlation of fasting blood, salivary glucose and malondialdehyde in subjects with & without type 2 diabetes

Oxidative stress is identified as the common pathogenic factor that leads to insulin resistance in diabetics. Malondialdehyde is a product of lipid peroxidation. Aim: The aim of this study was to determine the variation in the Salivary malondialdehyde (MDA) among subjects with and without T2DM in comparison to the fasting blood and Salivary glucose. Methods: This study involved 29 healthy participants as Controls (group I) and 29 participants with Type 2 Diabetes Mellitus as Cases (group II). Salivary Glucose was analysed by glucose oxidase end-point assay. Thiobarbituric acid (TBA) assay method was considered for estimation of MDA in fasting saliva. Data was Statistically analysed using SPSS20. Parametric test was performed to analyse the data. Results: The correlation calculated between FBG with FSG level was found to be highly significant. A positive correlation between MDA levels with FBG was found. The relationship between FBG and FSG (r = 0.7815, p < 0.05), FBG and MDA (r =0.3678, p < 0.05) and FSG and MDA (r = 0.2869, p < 0.05) were found to be positively significant. Conclusion: Saliva as a unique body fluid can serve as a medium for biochemical analysis only in standard settings and with multiple measures to be used as a diagnostic tool in par with the gold standard serum. Salivary MDA levels can be considered as one of the oxidative stress markers in Type 2 Diabetic condition

Prediction of Golgi Polarity in Collectively Migrating Epithelial Cells Using Graph Neural Network.

In the stationary epithelium, the Golgi apparatus assumes an apical position, above the cell nucleus. However, during wound healing and morphogenesis, as the epithelial cells starts migrating, it relocalizes closer to the basal plane. On this plane, the position of Golgi with respect to the cell nucleus defines the organizational polarity of a migrating epithelial cell, which is crucial for an efficient collective migration. Yet, factors influencing the Golgi polarity remain elusive. Here we constructed a graph neural network-based deep learning model to systematically analyze the dependency of Golgi polarity on multiple geometric and physical factors. In spite of the complexity of a migrating epithelial monolayer, our simple model was able to predict the Golgi polarity with 75% accuracy. Moreover, the model predicted that Golgi polarity predominantly correlates with the orientation of maximum principal stress. Finally, we found that this correlation operates locally since progressive coarsening of the stress field over multiple cell-lengths reduced the stress polarity-Golgi polarity correlation as well as the predictive accuracy of the neural network model. Taken together, our results demonstrated that graph neural networks could be a powerful tool towards understanding how different physical factors influence collective cell migration. They also highlighted a previously unknown role of physical cues in defining the intracellular organization.

Actin-driven Golgi apparatus dispersal during collective migration of epithelial cells.

As a sedentary epithelium turns motile during wound healing, morphogenesis, and metastasis, the Golgi apparatus moves from an apical position, above the nucleus, to a basal position. This apical-to-basal repositioning of Golgi is critical for epithelial cell migration. Yet the molecular mechanism underlying it remains elusive, although microtubules are believed to play a role. Using live-cell and super-resolution imaging, we show that at the onset of collective migration of epithelial cells, Golgi stacks get dispersed to create an unpolarized transitional structure, and surprisingly, this dispersal process depends not on microtubules but on actin cytoskeleton. Golgi-actin interaction involves Arp2/3-driven actin projections emanating from the actin cortex, and a Golgi-localized actin elongation factor, MENA. While in sedentary epithelial cells, actin projections intermittently interact with the apically located Golgi, and the frequency of this event increases before the dispersion of Golgi stacks, at the onset of cell migration. Preventing Golgi-actin interaction with MENA-mutants eliminates Golgi dispersion and reduces the persistence of cell migration. Taken together, we show a process of actin-driven Golgi dispersion that is mechanistically different from the well-known Golgi apparatus fragmentation during mitosis and is essential for collective migration of epithelial cells.

Aza-Quasi-Favorskii Reaction: Construction of Highly Substituted Aziridines through a Concerted Multibond Rearrangement Process.

A new molecular rearrangement, the aza-Quasi-Favorskii rearrangement, has been developed for the construction of highly substituted aziridines. Electron-deficient O-sulfonyl oximes react readily with α,α-disubstituted acetophenone-derived enolates to furnish highly substituted aziridines via this unprecedented domino process. In-depth computational studies reveal an asynchronous yet concerted nitrenoid-type rearrangement pathway.

Matrix mechanics regulates epithelial defence against cancer by tuning dynamic localization of filamin.

In epithelia, normal cells recognize and extrude out newly emerged transformed cells by competition. This process is the most fundamental epithelial defence against cancer, whose occasional failure promotes oncogenesis. However, little is known about what factors determine the success or failure of this defence. Here we report that mechanical stiffening of extracellular matrix attenuates the epithelial defence against HRasV12-transformed cells. Using photoconversion labelling, protein tracking, and loss-of-function mutations, we attribute this attenuation to stiffening-induced perinuclear sequestration of a cytoskeletal protein, filamin. On soft matrix mimicking healthy epithelium, filamin exists as a dynamically single population, which moves to the normal cell-transformed cell interface to initiate the extrusion of transformed cells. However, on stiff matrix mimicking fibrotic epithelium, filamin redistributes into two dynamically distinct populations, including a new perinuclear pool that cannot move to the cell-cell interface. A matrix stiffness-dependent differential between filamin-Cdc42 and filamin-perinuclear cytoskeleton interaction controls this distinctive filamin localization and hence, determines the success or failure of epithelial defence on soft versus stiff matrix. Together, our study reveals how pathological matrix stiffening leads to a failed epithelial defence at the initial stage of oncogenesis.

Insights Into Chemical Reactions at the Beginning of the Universe: From HeH+ to H3.

At the dawn of the Universe, the ions of the light elements produced in the Big Bang nucleosynthesis recombined with each other. In our present study, we have tried to mimic the conditions in the early Universe to show how the recombination process would have led to the formation of the first ever formed diatomic species of the Universe: HeH+, as well as the subsequent processes that would have led to the formation of the simplest triatomic species: H3 +. We have also studied some special cases: higher positive charge with fewer number of hydrogen atoms in a dense atmosphere, and the formation of unusual and interesting linear, dicationic He chains beginning from light elements He and H in a positively charged atmosphere. For all the simulations, the ab initio nanoreactor (AINR) dynamics method has been employed.

Unsymmetrical sp2 -sp3 Disilenes.

Disilenes with differently coordinated silicon atoms are not known. Here, we have shown the high yield synthesis of a range of disilenes (2-4 and 6) upon reaction of a hypersilyl silylene PhC(NtBu)2 SiSi(SiMe3 )3 (1) with aliphatic chlorophosphines. The most striking characteristic of these disilenes is the presence of two differently coordinated Si atoms (one is three-coordinated, the other four-coordinated). The analogous reaction with Ph2 PCl did not afford the desired disilene, but, surprisingly, led to the first tetraphosphinosilane (8). DFT calculations were performed to understand the bonding in disilenes and differences in reactivity of the complexes.

An excimer to exciplex transition through realization of donor-acceptor interactions in luminescent solvent-free liquids.

Luminescent solvent-free organic liquids are known for their enhanced quantum yield, color tunability, and availability of a matrix for other dopants to generate hybrid luminescent materials with improved features for newer applications. Herein, we report a donor-acceptor based luminescent "exciplex liquid" by utilizing the slightly different electron affinity of the acceptor molecules. A red-shifted broad exciplex emission exhibited by the donor-acceptor pair even at a lower concentration of the acceptor (0.001 equiv.) indicates high efficiency in the solvent-free state. A detailed NMR study revealed weak intermolecular interactions between the donor and acceptor in the solvent-free matrix that stabilizes the exciplex liquid. The failure of structurally similar solid counterparts to form an exciplex confirms the advantage of the available supportive liquid matrix. Besides, the luminescent exciplex liquid is found efficient in sensing application, which is unachievable by either the individual liquids or their solid counterparts. Here, a transition of a donor-acceptor pair from a solid to solvent-free liquid results in a new hybrid liquid that can be an alternative for solid sensor materials.

Diverse reactivity of carbenes and silylenes towards fluoropyridines.

The reaction of IDipp with C5F5N led to functionalization of all three carbon atoms of the imidazole ring with HF2- as the counter-anion (1). Reactivity with 2,3,5,6-tetrafluoropyridine gives only C-F bond activation leaving C-H bonds intact (5b). The reaction of SIDipp with C5F5N in the presence of BF3 afforded the ring cleavage product (3). Analogous reactions with silylene led to oxidative addition at the Si(ii) center.

Lithium compound catalyzed deoxygenative hydroboration of primary, secondary and tertiary amides.

A selective and efficient route for the deoxygenative reduction of primary to tertiary amides to corresponding amines has been achieved with pinacolborane (HBpin) using simple and readily accessible 2,6-di-tert-butyl phenolate lithium·THF (1a) as a catalyst. Both experimental and DFT studies provide mechanistic insight.

Access to diverse germylenes and a six-membered dialane with a flexible ß-diketiminate.

A nacnac-based tridentate ligand containing a picolyl group (L) was employed to isolate chlorogermylene (1). The reaction of 1 with another equivalent of GeCl2·dioxane surprisingly gave pyridylpyrrolide-based chlorogermylene (2) via C-N bond cleavage and C-C coupling, while with AlCl3, it afforded a transmetalated product, 4. The reaction of L with AlH3·NMe2Et led to an unusual cyclohexane type six-membered dialane heterocycle (5).

Imines as acceptors and donors in N-heterocyclic carbene (NHC) organocatalysis.

The synthetic potential of imines as electrophiles or as a source of nucleophilic coupling partner in N-heterocyclic carbene (NHC) catalysis for the synthesis of various nitrogen heterocycles and functionalized amines is highlighted in this Feature Article. Electrophilic imines are suitable candidates for intercepting the NHC-derived acyl anions, homoenolate equivalents, and (di)enolates for the synthesis of α-amino ketones and a variety of lactam derivatives. Moreover, enamines generated from imines bearing α-hydrogen could be trapped with α,ß-unsaturated acylazoliums for the synthesis of functionalized dihydropyridinones. NHCs are also useful for the umpolung of imines for the generation of aza-Breslow intermediates thus leading to the synthesis of indoles, quinolines, dihydroquinoxalines etc. A concise account of the diverse reactivity of imines in NHC catalysis has been presented.

Dynamic heterogeneity influences the leader-follower dynamics during epithelial wound closure.

Cells of epithelial tissue proliferate and pack together to attain an eventual density homeostasis. As the cell density increases, spatial distribution of velocity and force show striking similarity to the dynamic heterogeneity observed elsewhere in dense granular matter. While the physical nature of this heterogeneity is somewhat known in the epithelial cell monolayer, its biological relevance and precise connection to cell density remain elusive. Relevantly, we had demonstrated how large-scale dynamic heterogeneity in the monolayer stress field in the bulk could critically influence the emergence of leader cells at the wound margin during wound closure, but did not connect the observation to the corresponding cell density. In fact, numerous previous reports had essentially associated long-range force and velocity correlation with either cell density or dynamic heterogeneity, without any generalization. Here, we attempted to unify these two parameters under a single framework and explored their consequence on the dynamics of leader cells, which eventually affected the efficacy of collective migration and wound closure. To this end, we first quantified the dynamic heterogeneity by the peak height of four-point susceptibility. Remarkably, this quantity showed a linear relationship with cell density over many experimental samples. We then varied the heterogeneity, by changing cell density, and found this change altered the number of leader cells at the wound margin. At low heterogeneity, wound closure was slower, with decreased persistence, reduced coordination and disruptive leader-follower interactions. Finally, microscopic characterization of cell-substrate adhesions illustrated how heterogeneity influenced orientations of focal adhesions, affecting coordinated cell movements. Together, these results demonstrate the importance of dynamic heterogeneity in epithelial wound healing. This article is part of the theme issue 'Multi-scale analysis and modelling of collective migration in biological systems'.

Mechanobiology of leader-follower dynamics in epithelial cell migration.

Collective cell migration is fundamental to biological form and function. It is also relevant to the formation and repair of organs and to various pathological situations, including metastatic propagation of cancer. Technological, experimental, and computational advancements have allowed the researchers to explore various aspects of collective migration, spanning from biochemical signalling to inter-cellular force transduction. Here, we summarize our current understanding of the mechanobiology of collective cell migration, limiting to epithelial tissues. On the basis of recent studies, we describe how cells sense and respond to guidance signals to orchestrate various modes of migration and identify the determining factors dictating leader-follower interactions. We highlight how the inherent mechanics of dense epithelial monolayers at multicellular length scale might instruct individual cells to behave collectively. On the basis of these findings, we propose that mechanical resilience, obtained by a certain extent of cell jamming, allows the epithelium to perform efficient collective migration during wound healing.

N-Heterocyclic Carbene Catalysis Exploiting Oxidative Imine Umpolung for the Generation of Imidoyl Azoliums.

Although NHC-catalyzed umpolung of imines are known, the related reactions under oxidative conditions are limited. Described herein is the two-step process involving the initial formation of aldimines from the corresponding aldehydes and 2-amino benzyl alcohols followed by NHC-catalyzed cyclization proceeding via the imidoyl azoliums under oxidative conditions. The reaction allowed the synthesis of trifluoromethylated 3,1-benzoxazines in good yields and broad scope. The role of NHC in the intramolecular cyclization and preliminary mechanistic experiments are also provided.