circPVT1 promotes silica-induced epithelial-mesenchymal transition by modulating the miR-497-5p/TCF3 axis.

Epithelial-mesenchymal transition (EMT) is a vital pathological feature of silica-induced pulmonary fibrosis. However, whether circRNA is involved in the process remains unclear. The present study aimed to investigate the role of circPVT1 in the silica-induced EMT and the underlying mechanisms. We found that an elevated expression of circPVT1 promoted EMT and enhanced the migratory capacity of silica-treated epithelial cells. The isolation of cytoplasmic and nuclear separation assay showed that circPVT1 was predominantly expressed in the cytoplasm. RNA immunoprecipitation assay and RNA pull-down experiment indicated that cytoplasmic-localized circPVT1 was capable of binding to miR-497-5p. Furthermore, we found that miR-497-5p attenuated the silica-induced EMT process by targeting transcription factor 3 (TCF3), an E-cadherin transcriptional repressor, in the silica-treated epithelial cells. Collectively, these results reveal a novel role of the circPVT1/miR-497-5p/TCF3 axis in the silica-induced EMT process in lung epithelial cells. Once validated, this finding may provide a potential theoretical basis for the development of interventions and treatments for pulmonary fibrosis.

Synergetic Conformational Regulations in Ground and Excited States for Realizing Stimulus-Responsive and Wide-Tuning Room-Temperature Phosphorescence.

Understanding the changes of molecular conformations is crucial for realizing multiple emissive triplet states in room-temperature phosphorescence (RTP) materials. In this work, we report two molecules, 4,4'-dimethylbenzil (DMBZ) and 4,4'-di-tert-butylbenzil (DBBZ) with conformation-dependent luminescence, and demonstrate that stimulus-responsive and wide-tuning RTP emissions can be realized via synergetic conformational regulations in ground and excited states. Due to conformational changes, DMBZ and DBBZ show abundant RTP variations upon external stimuli, including light, force, heat, and fumigation. Notably, DBBZ exhibits multiple conformational changes in both ground and excited states, which endow DBBZ with multiple emissive states and unique stimulus-responsive behaviors. DBBZ presents multiple phase transitions between the supercooled liquid state and different solid states accompanied by different phosphorescence transitions, in which the excited-state conformations are effectively regulated. Moreover, wide-range RTP regulations (between cyan, green, and yellow) are realized in both single component and host-guest systems of DBBZ, showing potential applications in temperature sensing, multicolor dynamic displays, and information encryption. These results may provide new visions for understanding the complicated conformational changes in the aggregated state, as well as unique insights into the relationship between molecular conformations, RTP emissions, and stimulus responsiveness.

A dish-like molecular architecture for dynamic ultralong room-temperature phosphorescence through reversible guest accommodation.

Developing dynamic organic ultralong room-temperature phosphorescent (URTP) materials is of practical importance in various applications but remains a challenge due to the difficulty in manipulating aggregate structures. Herein, we report a dish-like molecular architecture via a bottom-up way, featuring guest-responsive dynamic URTP. Through controlling local fragment motions in the molecular architecture, fascinating dynamic URTP performances can be achieved in response to reversible accommodation of various guests, including solvents, alkyl bromides and even carbon dioxide. Large-scale regulations of phosphorescence lifetime (100-fold) and intensity (10-fold) can be realized, presenting a maximum phosphorescence efficiency and lifetime of 78.8% and 483.1 ms, respectively. Moreover, such a dish-like molecular architecture is employed for temperature-dependent multiple information encryption and visual identification of linear alkyl bromides. This work can not only deepen our understanding to construct multifunctional organic aggregates, but also facilitate the design of high-performance dynamic URTP materials and enrich their practical applications.

UHRF1-mediated ferroptosis promotes pulmonary fibrosis via epigenetic repression of GPX4 and FSP1 genes.

Pulmonary fibrosis (PF), as an end-stage clinical phenotype of interstitial lung diseases (ILDs), is frequently initiated after alveolar injury, in which ferroptosis has been identified as a critical event aggravating the pathophysiological progression of this disease. Here in, a comprehensive analysis of two mouse models of pulmonary fibrosis developed in our lab demonstrated that lung damage-induced ferroptosis of alveolar epithelial Type2 cells (AEC2) significantly accumulates during the development of pulmonary fibrosis while ferroptosis suppressor genes GPX4 and FSP1 are dramatically inactivated. Mechanistically, upregulation of de novo methylation regulator Uhrf1 sensitively elevates CpG site methylation levels in promoters of both GPX4 and FSP1 genes and induces the epigenetic repression of both genes, subsequently leading to ferroptosis in chemically interfered AEC2 cells. Meanwhile, specific inhibition of UHRF1 highly arrests the ferroptosis formation and blocks the progression of pulmonary fibrosis in both of our research models. This study first, to our knowledge, identified the involvement of Uhrf1 in mediating the ferroptosis of chemically injured AEC2s via de novo promoter-specific methylation of both GPX4 and FSP1 genes, which consequently accelerates the process of pulmonary fibrosis. The above findings also strongly suggested Uhrf1 as a novel potential target in the treatment of pulmonary fibrosis.

Caveolin-1 and Its Functional Peptide CSP7 Affect Silica-Induced Pulmonary Fibrosis by Regulating Fibroblast Glutaminolysis.

Exposure to silica is a cause of pulmonary fibrosis disease termed silicosis, which leads to respiratory failure and ultimately death. However, what drives fibrosis is not fully elucidated and therapeutic options remain limited. Our previous RNA-sequencing analysis showed that the expression of caveolin-1 (CAV1) was downregulated in silica-inhaled mouse lung tissues. Here, we not only verified that CAV1 was decreased in silica-induced fibrotic mouse lung tissues in both messenger RNA and protein levels, but also found that CSP7, a functional peptide of CAV1, could attenuate pulmonary fibrosis in vivo. Further in vitro experiments revealed that CAV1 reduced the expression of Yes-associated protein 1(YAP1) and affected its nuclear translocation in fibroblasts. In addition, Glutaminase 1 (GLS1), a key regulator of glutaminolysis, was identified to be a downstream effector of YAP1. CAV1 could suppress the activity of YAP1 to decrease the transcription of GLS1, thereby inhibiting fibroblast activation. Taken together, our results demonstrated that CAV1 and its functional peptide CSP7 may be potential molecules or drugs for the prevention and intervention of silicosis.

Structurally Resemblant Dopants Enhance Organic Room-Temperature Phosphorescence.

Doping has shown very promising potential in endowing room-temperature phosphorescence (RTP) properties of organic phosphors with minimal effort. Here, a new isomer design and doping strategy is reported that is applicable to dibenzothiophene (DBT) and its derivatives. Three isomers are synthesized to study the dopant effect on enhancing RTP of DBT derivatives. It is found that isomer dopants bearing close resemblance to the host with matched highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and small energy difference between singlet- and triplet-excited states can yield efficient RTP for the doped system. Meanwhile, phosphorescence color from yellow to red is achieved by varying isomer dopants used for doping the DBT derivatives. This work represents an RTP enhancement strategy based on isomer design and doping to construct luminescent organic phosphors.

ALKBH5 promotes lung fibroblast activation and silica-induced pulmonary fibrosis through miR-320a-3p and FOXM1.

BACKGROUND: N6-methyladenosine (m6A) is the most common and abundant internal modification of RNA. Its critical functions in multiple physiological and pathological processes have been reported. However, the role of m6A in silica-induced pulmonary fibrosis has not been fully elucidated. AlkB homolog 5 (ALKBH5), a well-known m6A demethylase, is upregulated in the silica-induced mouse pulmonary fibrosis model. Here, we sought to investigate the function of ALKBH5 in pulmonary fibrosis triggered by silica inhalation. METHODS: We performed studies with fibroblast cell lines and silica-induced mouse pulmonary fibrosis models. The expression of ALKBH5, miR-320a-3p, and forkhead box protein M1 (FOXM1) was determined by quantitative real-time polymerase chain reaction (qRT-PCR) analysis. RNA immunoprecipitation (RIP) assays and m6A RNA immunoprecipitation assays (MeRIP), western bolt, immunofluorescence assays, and 5-ethynyl-2'-deoxyuridine (EdU) fluorescence staining were performed to explore the roles of ALKBH5, miR-320a-3p, and FOXM1 in fibroblast activation. RESULTS: ALKBH5 expression was increased in silica-inhaled mouse lung tissues and transforming growth factor (TGF)-ß1-stimulated fibroblasts. Moreover, ALKBH5 knockdown exerted antifibrotic effects in vitro. Simultaneously, downregulation of ALKBH5 elevated miR-320a-3p but decreased pri-miR-320a-3p. Mechanically, ALKBH5 demethylated pri-miR-320a-3p, thus blocking the microprocessor protein DGCR8 from interacting with pri-miR-320a-3p and leading to mature process blockage of pri-miR-320a-3p. We further demonstrated that miR-320a-3p could regulate fibrosis by targeting FOXM1 messenger RNA (mRNA) 3'-untranslated region (UTR). Notably, our study also verified that ALKBH5 could also directly regulate FOXM1 in an m6A-dependent manner. CONCLUSIONS: Our findings suggest that ALKBH5 promotes silica-induced lung fibrosis via the miR-320a-3p/FOXM1 axis or targeting FOXM1 directly. Approaches aimed at ALKBH5 may be efficacious in treating lung fibrosis.

PTX3 alleviates hard metal-induced acute lung injury through potentiating efferocytosis.

Prolonged exposure to hard metal dust results in hard metal lung disease (HMLD) characterized by respiratory symptoms. Understanding the pathogenesis and pathological process of HMLD would be helpful for its early diagnosis and treatment. In this study, we established a mouse model of hard metal-induced acute lung injury through one-time intratracheal instillation of WC-Co dust suspension. We found that WC-Co treatment damaged the lungs of mice, leading to increased production of IL-1ß, TNF-α, IL-6 and IL-18, inflammatory cells infiltration and apoptosis. In vitro, WC-Co induced cytotoxicity, inflammatory response and apoptosis in macrophages (PMA-treated THP-1) and epithelial cells (A549) in a dose-dependent manner. Moreover, RNA-sequence and validation experiments verified that Pentraxin 3 (PTX3), an important mediator in the regulation of inflammation, was elevated both in vivo and in vitro induced by WC-Co. Functional experiments confirmed the PTX3, which was located on the membrane of apoptotic cells, promoted macrophage efferocytosis efficiently. This progress could help block the lung inflammation and contribute to the rapid recovery of WC-Co-induced acute lung injury. These observations provide a further understanding of the molecular mechanism of WC-Co-induced pulmonary injury and disclose PTX3 as a new potential therapeutic approach to relieve WC-Co-induced acute lung injury via efferocytosis.

Metformin attenuates silica-induced pulmonary fibrosis via AMPK signaling.

BACKGROUND: Silicosis is one of the most common occupational pulmonary fibrosis caused by respirable silica-based particle exposure, with no ideal drugs at present. Metformin, a commonly used biguanide antidiabetic agent, could activate AMP-activated protein kinase (AMPK) to exert its pharmacological action. Therefore, we sought to investigate the role of metformin in silica-induced lung fibrosis. METHODS: The anti-fibrotic role of metformin was assessed in 50 mg/kg silica-induced lung fibrosis model. Silicon dioxide (SiO2)-stimulated lung epithelial cells/macrophages and transforming growth factor-beta 1 (TGF-ß1)-induced differentiated lung fibroblasts were used for in vitro models. RESULTS: At the concentration of 300 mg/kg in the mouse model, metformin significantly reduced lung inflammation and fibrosis in SiO2-instilled mice at the early and late fibrotic stages. Besides, metformin (range 2-10 mM) reversed SiO2-induced cell toxicity, oxidative stress, and epithelial-mesenchymal transition process in epithelial cells (A549 and HBE), inhibited inflammation response in macrophages (THP-1), and alleviated TGF-ß1-stimulated fibroblast activation in lung fibroblasts (MRC-5) via an AMPK-dependent pathway. CONCLUSIONS: In this study, we identified that metformin might be a potential drug for silicosis treatment.

CircHIPK3 regulates pulmonary fibrosis by facilitating glycolysis in miR-30a-3p/FOXK2-dependent manner.

Pulmonary fibrosis develops when myofibroblasts and extracellular matrix excessively accumulate in the injured lung, but what drives fibrosis is not fully understood. Glycolysis has been linked to cell growth and proliferation, and several studies have shown enhanced glycolysis promotes pulmonary fibrosis. However, detailed studies describing this switch remain limited. Here, we identified that TGF-ß1 effectively increased the expression of circHIPK3 in lung fibroblasts, and circHIPK3 inhibition attenuated the activation, proliferation, and glycolysis of fibroblasts in vitro. Dual-luciferase reporter gene assays, RNA immunoprecipitation (RIP), and RNA pull-down assays showed that circHIPK3 could function as a sponge of miR-30a-3p and inhibit its expression. Furthermore, FOXK2, a driver transcription factor of glycolysis, was identified to be a direct target of miR-30a-3p. Mechanistically, circHIPK3 could enhance the expression of FOXK2 via sponging miR-30a-3p, thereby facilitating fibroblast glycolysis and activation. Besides, miR-30a-3p overexpression or FOXK2 knockdown blocked fibroblast activation induced by TGF-ß1 and abrogated the profibrotic effects of circHIPK3. Moreover, circHIPK3 and miR-30a-3p were also dysregulated in fibrotic murine lung tissues induced by silica. Adeno-associated virus (AAV)-mediated circHIPK3 silence or miR-30a-3p overexpression alleviated silica-induced pulmonary fibrosis in vivo. In conclusion, our results identified circHIPK3/miR-30a-3p/FOXK2 regulatory pathway as an important glycolysis cascade in pulmonary fibrosis.

LncRNA-ATB regulates epithelial-mesenchymal transition progression in pulmonary fibrosis via sponging miR-29b-2-5p and miR-34c-3p.

Dysregulation of non-coding RNAs (ncRNAs) has been proved to play pivotal roles in epithelial-mesenchymal transition (EMT) and fibrosis. We have previously demonstrated the crucial function of long non-coding RNA (lncRNA) ATB in silica-induced pulmonary fibrosis-related EMT progression. However, the underlying molecular mechanism has not been fully elucidated. Here, we verified miR-29b-2-5p and miR-34c-3p as two vital downstream targets of lncRNA-ATB. As opposed to lncRNA-ATB, a significant reduction of both miR-29b-2-5p and miR-34c-3p was observed in lung epithelial cells treated with TGF-ß1 and a murine silicosis model. Overexpression miR-29b-2-5p or miR-34c-3p inhibited EMT process and abrogated the pro-fibrotic effects of lncRNA-ATB in vitro. Further, the ectopic expression of miR-29b-2-5p and miR-34c-3p with chemotherapy attenuated silica-induced pulmonary fibrosis in vivo. Mechanistically, TGF-ß1-induced lncRNA-ATB accelerated EMT as a sponge of miR-29b-2-5p and miR-34c-3p and shared miRNA response elements with MEKK2 and NOTCH2, thus relieving these two molecules from miRNA-mediated translational repression. Interestingly, the co-transfection of miR-29b-2-5p and miR-34c-3p showed a synergistic suppression effect on EMT in vitro. Furthermore, the co-expression of these two miRNAs by using adeno-associated virus (AAV) better alleviated silica-induced fibrogenesis than single miRNA. Approaches aiming at lncRNA-ATB and its downstream effectors may represent new effective therapeutic strategies in pulmonary fibrosis.

An Effective Strategy of Combining Surface Passivation and Secondary Grain Growth for Highly Efficient and Stable Perovskite Solar Cells.

Interfacial engineering methods have been developed to solve defect issues of perovskite solar cells (PSCs). However, traditional surface passivation has limited effects on eliminating defect-forming residuals, while secondary grain growth (SGG) is restricted by limited choices of additives and intrinsic properties of perovskites. Here, a pincer strategy of taking advantages of surface passivation and SGG is proposed to modify both exterior and interior of CH3 NH3 PbI3 (MAPbI3 ) perovskite, by employing cyanoacetate-containing donor-acceptor compounds (CA-D-A) including 2-cyano-3-(3,4,5-trimethoxyphenyl)acrylic acid (CA), methanaminium 2-cyano-3-(3,4,5-trimethoxyphenyl)acrylate (CAMA), and aminomethaniminium (Z)-2-cyano-3-(3,4,5-trimethoxyphenyl)acrylate (CAFA). In comparison to untreated perovskite, CA-D-A treated perovskites present better crystallinity because of SGG, lower trap densities due to the synergistic effect of surface passivation and SGG, and tuned energy levels induced by CA-D-A. Accordingly, the CA-D-A treated MAPbI3 -based PSCs exhibit higher open-circuit voltage and fill factor than the control PSC without any treatment, leading to improved power conversion efficiency (PCE) and enhanced device stability, especially the CAMA treated PSCs with an average PCE promoted from 17.77 (control PSCs) to 18.71%, and importantly an excellent PCE of 19.71% through further optimization. This work provides an effective strategy for developing highly efficient and stable PSCs with the assistance of both surface passivation and SGG.

Long noncoding RNA-SNHG20 promotes silica-induced pulmonary fibrosis by miR-490-3p/TGFBR1 axis.

Silicosis is a universal occupational disease, which is caused by long-term crystalline silica exposure. Recent studies have shown that noncoding RNAs participate in diverse pathological cellular pathways. However, the precise regulation mechanism remains limited in silicosis. Here, we established a silica-induced mouse fibrosis model (all mice received a one-time intratracheal instillation with 50 mg/kg of silica in 0.05 mL sterile saline). MiR-490-3p was significantly downregulated in silica-induced fibrotic mouse lung tissues and TGF-ß1 treated fibroblasts. Moreover, overexpressed miR-490-3p could relieve silica-induced lung fibrosis in vivo, and prevent the process of fibroblast-to-myofibroblast transition(FMT)in vitro. Mechanistically, TGFBR1 was one of the major target genes of miR-490-3p, and tightly associated with the process of fibroblasts activation. SNHG20, as opposed to miR-490-3p expression, was elevated in TGF-ß1-treated fibroblast cell lines and contributed to decreased levels of miR-490-3p. Taken together, these data indicated that miR-490-3p plays a key role in silica-induced pulmonary fibrosis. Our results suggested that SNHG20/miR-490-3p/TGFBR1 axis may provide a new treatment target of pulmonary fibrosis.

Activating Versatile Mechanoluminescence in Organic Host-Guest Crystals by Controlling Exciton Transfer.

Mechanoluminescence (ML) materials are attracting increasing interest owing to promising applications in various areas. However, to date, it remains a major challenge to develop a precise and universal route to achieving organic ML materials. Herein, we show that ML can be easily realized in organic piezophotonic host-guest crystals, under conditions in which neither the host nor the guest is ML-active. The experimental and theoretical results reveal that excitons of the host generated by piezoelectricity can be harvested effectively by the guest for light emission, owing to the restraint of intersystem crossing process. Moreover, different host-guest crystals are constructed, wherein the emission color, intensity, color purity, and emission duration of ML can be manipulated. This work deepens our understanding of organic ML generation in piezophotonic host-guest crystals and provides an inspiring principle to design more organic ML materials.

The Functional Availability of Arterial Kv7 Channels Is Suppressed Considerably by Large-Conductance Calcium-Activated Potassium Channels in 2- to 3-Month Old but Not in 10- to 15-Day Old Rats.

BACKGROUND: Voltage-gated potassium (Kv) channels, especially Kv7 channels, are major potassium channels identified in vascular smooth muscle cells with a great, albeit differential functional impact in various vessels. Vascular smooth muscle Kv7 channels always coexist with other K channels, in particular with BK channels. BK channels differ in the extent to which they influence vascular contractility. Whether this difference also causes the variability in the functional impact of Kv7 channels is unknown. Therefore, this study addressed the hypothesis that the functional impact of Kv7 channels depends on BK channels. EXPERIMENTAL APPROACH: Experiments were performed on young and adult rat gracilis and saphenous arteries using real-time PCR as well as pressure and wire myography. KEY RESULTS: Several subfamily members of Kv7 (KCNQ) and BK channels were expressed in saphenous and gracilis arteries: the highest expression was observed for BKα, BKß1 and KCNQ4. Arterial contractility was assessed with methoxamine-induced contractions and pressure-induced myogenic responses. In vessels of adult rats, inhibition of Kv7 channels or BK channels by XE991 or IBTX, respectively enhanced arterial contractility to a similar degree, whereas activation of Kv7 channels or BK channels by retigabine or NS19504, respectively reduced arterial contractility to a similar degree. Further, IBTX increased both the contractile effect of XE991 and the anticontractile effect of retigabine, whereas NS19504 reduced the effect of retigabine and impaired the effect of XE991. In vessels of young rats, inhibition of Kv7 channels by XE991 enhanced arterial contractility much stronger than inhibition of BK channels by IBTX, whereas activation of Kv7 by retigabine reduced arterial contractility to a greater extent than activation of BK channels by NS19504. Further, IBTX increased the anticontractile effect of retigabine but not the contractile effect of XE991, whereas NS19504 reduced the effect of retigabine and impaired the effect of XE991. CONCLUSION: Kv7 and BK channels are expressed in young and adult rat arteries and function as negative feedback modulators in the regulation of contractility of these arteries. Importantly, BK channels govern the extent of functional impact of Kv7 channels. This effect depends on the relationship between the functional activities of BK and Kv7 channels.

Vasodilation of rat skeletal muscle arteries by the novel BK channel opener GoSlo is mediated by the simultaneous activation of BK and Kv 7 channels.

BACKGROUND AND PURPOSE: BK channels play important roles in various physiological and pathophysiological processes and thus have been the target of several drug development programmes focused on creating new efficacious BK channel openers, such as the GoSlo-SR compounds. However, the effect of GoSlo-SR compounds on vascular smooth muscle has not been studied. Therefore, we tested the hypothesis that GoSlo-SR compounds dilate arteries exclusively by activating BK channels. EXPERIMENTAL APPROACH: Experiments were performed on rat Gracilis muscle, saphenous, mesenteric and tail arteries using isobaric and isometric myography, sharp microelectrodes, digital droplet PCR and the patch-clamp technique. KEY RESULTS: GoSlo-SR compounds dilated isobaric and relaxed and hyperpolarised isometric vessel preparations and their effects were abolished after (a) functionally eliminating K+ channels by pre-constriction with 50 mM KCl or (b) blocking all K+ channels known to be expressed in vascular smooth muscle. However, these effects were not blocked when BK channels were inhibited. Surprisingly, the Kv 7 channel inhibitor XE991 reduced their effects considerably, but neither Kv 1 nor Kv 2 channel blockers altered the inhibitory effects of GoSlo-SR. However, the combined blockade of BK and Kv 7 channels abolished the GoSlo-SR-induced relaxation. GoSlo-SR compounds also activated Kv 7.4 and Kv 7.5 channels expressed in HEK 293 cells. CONCLUSION AND IMPLICATIONS: This study shows that GoSlo-SR compounds are effective relaxants in vascular smooth muscle and mediate their effects by a combined activation of BK and Kv 7.4/Kv 7.5 channels. Activation of Kv 1, Kv 2 or Kv 7.1 channels or other vasodilator pathways seems not to be involved.

Nanoassembly and Multiscale Computation of Multifunctional Optical-Magnetic Nanoprobes for Tumor-Targeted Theranostics.

Gold nanorods, mesoporous silica, gadolinia, folic acid, and polyethylene glycol (PEG) derivatives have been investigated due to their own advantages in cancer theranostics. However, it remains a great challenge to assemble these components into a stable unity with the diverse and enhanced functionality for more potential applications. Herein, as inspired by the first-principles calculation, a highly stable and safe all-in-one nanoprobe is fabricated via a novel nanoassembly strategy. Multiscale calculations were performed to address the atomistic bonding of a nanoprobe, heat necrosis of a tumor adjacent to the vasculature, and thermal diffusion in a photothermal circumstance, respectively. The nanoprobe gains an 8-fold increase in magnetic resonance imaging (MRI) relaxivity compared to the clinical gadolinium diethylenetriaminepentaacetate, achieving a significant MRI signal in vivo. Conjugated with folate-PEG, the nanoprobe can be effectively absorbed by tumoral cells, obtaining a vivid two-photon cell imaging. A specific multisite scheme for photothermal therapy of a solid tumor is proposed to improve low photothermal efficacy caused by thermal diffusion in a large tumor, leading to the successful cure of the mice with xenograft tumor sized 10-12 mm. In vitro and in vivo toxicity, long-term excretion data, and the recovery of the treated mice demonstrate that the theranostic nanoprobe possesses good biocompatibility and metabolism efficacy.

A transient ischemic environment induces reversible compaction of chromatin.

BACKGROUND: Cells detect and adapt to hypoxic and nutritional stress through immediate transcriptional, translational and metabolic responses. The environmental effects of ischemia on chromatin nanostructure were investigated using single molecule localization microscopy of DNA binding dyes and of acetylated histones, by the sensitivity of chromatin to digestion with DNAseI, and by fluorescence recovery after photobleaching (FRAP) of core and linker histones. RESULTS: Short-term oxygen and nutrient deprivation of the cardiomyocyte cell line HL-1 induces a previously undescribed chromatin architecture, consisting of large, chromatin-sparse voids interspersed between DNA-dense hollow helicoid structures 40-700 nm in dimension. The chromatin compaction is reversible, and upon restitution of normoxia and nutrients, chromatin transiently adopts a more open structure than in untreated cells. The compacted state of chromatin reduces transcription, while the open chromatin structure induced upon recovery provokes a transitory increase in transcription. Digestion of chromatin with DNAseI confirms that oxygen and nutrient deprivation induces compaction of chromatin. Chromatin compaction is associated with depletion of ATP and redistribution of the polyamine pool into the nucleus. FRAP demonstrates that core histones are not displaced from compacted chromatin; however, the mobility of linker histone H1 is considerably reduced, to an extent that far exceeds the difference in histone H1 mobility between heterochromatin and euchromatin. CONCLUSIONS: These studies exemplify the dynamic capacity of chromatin architecture to physically respond to environmental conditions, directly link cellular energy status to chromatin compaction and provide insight into the effect ischemia has on the nuclear architecture of cells.