Cell Shortening Research Articles

Different effects of cardiomyocyte contractile activity on transverse and axial tubular system luminal content dynamics

BackgroundEfficient excitation-contraction coupling of mammalian ventricular cardiomyocytes depends on the transverse − axial tubular system (TATS), a network of surface membrane invaginations. TATS enables tight coupling of sarcolemmal and sarcoplasmic reticulum membranes, which is essential for rapid Ca2+-induced Ca2+ release, and uniform contraction upon electrical stimulation. The majority of TATS in healthy ventricular cardiomyocytes is composed of transverse tubules (TT, ~90 % of TATS in rabbit). The remainder consists of mostly axial tubules (AT), which are less abundant and less well studied. In disease, however, the relative abundance of TT and AT changes. The mechanisms and relevance of this change are not known, and understanding them requires a more targeted effort to study the dynamics of AT structure and function.While TATS content is continuous with the interstitial space, it is contained within a domain of restricted diffusion. We have previously shown that TT are cyclically squeezed during stretch and contraction. This can contribute to TT content mixing and accelerates luminal content exchange with the environment. Here, we explore the effects of cardiomyocyte stretch and contraction on AT. MethodsTATS structure and diffusion dynamics were studied using 3D electron tomography of rabbit left ventricular cardiomyocytes, preserved at rest or during contraction, and ventricular tissue preserved at rest or during stretch, as well as live-cell TATS content exchange measurements. ResultsWe show (i) that cardiomyocyte contraction is associated with an increase in the apparent speed of diffusion of TT content that scales with beating rate and degree of cell shortening. In contrast, (ii) AT develop membrane folds and constrictions during contraction, (iii) with no effect of contraction on luminal exchange dynamics, while (iv) cardiomyocyte stretch is associated with AT straightening and AT and TT ‘squeezing’ that (v) supports an acceleration of the apparent speed of diffusion in AT and TT. Finally, (vi) we present a simple computational model outlining the potential relevance of AT in healthy and diseased cells. ConclusionsOur results indicate that TT and AT are differently affected by the cardiac contractile cycle, and suggest that AT may play a role in ensuring TATS network content homogeneity in diseased cardiomyocytes. Further research is needed to explore the interplay of structural and functional remodelling of different TATS components in failing myocardium.

Activation of protein kinase B rescues against thapsigargin-elicited cardiac dysfunction through regulation of NADPH oxidase and ferroptosis

Endoplasmic reticulum (ER) stress is a known contributor to cardiac remodeling and contractile dysfunction. Although NADPH oxidase has been implicated in ER stress-induced organ damage, its specific role in myocardial complications resulting from ER stress remains unclear. This study aimed to investigate the possible involvement of NADPH oxidase in ER stress-induced myocardial abnormalities and to evaluate the impact of Akt constitutive activation on these myocardial defects. Mice with cardiac-specific overexpression of active mutant of Akt (Myr-Akt) and their wild-type (WT) littermates were treated with ER stress instigator thapsigargin (1 mg/kg, i. p. 72 hrs) before evaluating myocardial morphology and function. Our results noted that thapsigargin significantly impaired echocardiographic parameters and cell shortening indices, including elevated LVESD, decreased ejection fraction, fractional shortening, peak shortening, electrically-stimulated intracellular Ca2+ release, and cardiomyocyte survival. These functional deteriorations were accompanied by upregulation of NADPH oxidase, O2− production, mitochondrial damage, carbonyl formation, lipid peroxidation, apoptosis, and interstitial fibrosis, with unchanged myocardial size. Constitutive Akt hyperactivation did not generate any response on myocardial morphology and function, although it greatly suppressed or nullified thapsigargin-induced myocardial remodeling and dysfunction. Thapsigargin also triggered dephosphorylation of Akt and its downstream signal GSK3β, along with development of ferroptosis, all of which were nullified by Akt hyperactivation. In vitro studies further revealed that thapsigargin provoked cardiomyocyte mechanical anomalies and lipid peroxidation, similar to in vivo results. These effects were reverted by inhibitors of NADPH oxidase and ferroptosis (apocynin and LIP1). Collectively, our data denote an important protective role for Akt hyperactivation in thapsigargin-evoked myocardial anomalies, likely through NADPH oxidase-mediated regulation of ferroptosis.

Targeting telomerase with MST-312 leads to downregulation of CCND1, MDM2, MYC, and HSP90AA1 and induce apoptosis in Jurkat cell line.

Acute lymphoblastic leukemia is a challenging disease to treat, especially in older adults who are most commonly diagnosed and have a high risk of relapse, even with current treatment options. MST-312, targets the RNA component of telomerase, inhibiting its activity and leading to growth arrest and telomere shortening in cancer cells. This study aimed to investigate the effects of MST-312 on apoptosis rates and the expression of telomerase target genes, CCND1, MDM2, MYC, and HSP90AA1, in Jurkat cell line. Jurkat cell line was cultured and treated with various concentrations of MST-312(0 µM, 0.5 µM, 1 µM, 2 µM, and 4 µM). The optimal concentration of MST-312 was determined using MTT assay. Flow cytometry was employed to evaluate the apoptosis induced by MST-312 treatment. The expression levels of the target genes were measured using real-time polymerase chain reaction before and after the treatment with MST-312. P-value < 0.05 was considered statistically significant. The percentages of apoptotic cells after 48 h, as determined by flow cytometry analysis, were 30.32%, 52.35%, 57.60%, and 68.82%, respectively, compared to the control group which was 4.6%. The expression levels of all genes, including CCND1, MDM2, MYC, and HSP90AA1, were decreased compared to the control group. The results showed that MST-312 induced dose- and time-dependent apoptosis and downregulated the expression of CCND1, MDM2, MYC, and HSP90AA1in Jurkat cell line.

Connecting the Dots: Telomere Shortening and Rheumatic Diseases.

Telomeres, repetitive sequences located at the extremities of chromosomes, play a pivotal role in sustaining chromosomal stability. Telomerase is a complex enzyme that can elongate telomeres by appending telomeric repeats to chromosome ends and acts as a critical factor in telomere dynamics. The gradual shortening of telomeres over time is a hallmark of cellular senescence and cellular death. Notably, telomere shortening appears to result from the complex interplay of two primary mechanisms: telomere shelterin complexes and telomerase activity. The intricate interplay of genetic, environmental, and lifestyle influences can perturb telomere replication, incite oxidative stress damage, and modulate telomerase activity, collectively resulting in shifts in telomere length. This age-related process of telomere shortening plays a considerable role in various chronic inflammatory and oxidative stress conditions, including cancer, cardiovascular disease, and rheumatic disease. Existing evidence has shown that abnormal telomere shortening or telomerase activity abnormalities are present in the pathophysiological processes of most rheumatic diseases, including different disease stages and cell types. The impact of telomere shortening on rheumatic diseases is multifaceted. This review summarizes the current understanding of the link between telomere length and rheumatic diseases in clinical patients and examines probable telomere shortening in peripheral blood mononuclear cells and histiocytes. Therefore, understanding the intricate interaction between telomere shortening and various rheumatic diseases will help in designing personalized treatment and control measures for rheumatic disease.

Effect of aging and exercise on hTERT expression in thymus tissue of hTERT transgenic bacterial artificial chromosome mice.

Telomere shortening occurs with aging in immune cells and may be related to immunosenescence. Exercise can upregulate telomerase activity and attenuate telomere shortening in immune cells, but it is unknown if exercise impacts other immune tissues such as the thymus. This study aimed to examine human telomerase reverse transcriptase (hTERT) alternative splicing (AS) in response to aging and exercise in thymus tissue. Transgenic mice with a human TERT bacterial artificial chromosome integrated into its genome (hTERT-BAC) were utilized in two different exercise models. Mice of different ages were assigned to an exercise cage (running wheel) or not for 3weeks prior to thymus tissue excision. Middle-aged mice (16months) were exposed or not to treadmill running (30min at 60% maximum speed) prior to thymus collection. hTERT transcript variants were measured by RT-PCR. hTERT transcripts decreased with aging (r = - 0.7511, p < 0.0001) and 3weeks of wheel running did not counteract this reduction. The ratio of exons 7/8 containing hTERT to total hTERT transcripts increased with aging (r = 0.3669, p = 0.0423) but 3weeks of voluntary wheel running attenuated this aging-driven effect (r = 0.2013, p = 0.4719). Aging increased the expression of senescence marker p16 with no impact of wheel running. Thymus regeneration transcription factor, Foxn1, went down with age with no impact of wheel running exercise. Acute treadmill exercise did not induce any significant changes in thymus hTERT expression or AS variant ratio (p > 0.05). In summary, thymic hTERT expression is reduced with aging. Exercise counteracted a shift in hTERT AS ratio with age. Our data demonstrate that aging impacts telomerase expression and that exercise impacts dysregulated splicing that occurs with aging.

Abstract Mo070: Metabolic Syndrome Alters cAMP Homeostasis and Contractile Function of Cardiomyocytes

Approximately one third of the population in the US has metabolic syndrome (MetS), a condition associated with increased risk for coronary artery disease and myocardial infarction. But whether MetS alters properties of the myocardium before the occurrence of ischemic insults remains to be fully elucidated. For this purpose, MetS was induced in C57Bl/6 female mice with a dietary paradigm recapitulating Western-style alimentary habits in humans. Animals on regular chow were used as control (Ctrl). Cardiac function was assessed by echocardiography and myocytes were studied under field stimulation, following enzymatic dissociation. From 3-12 months on the diet, MetS mice had increased body weight, impaired glucose metabolism, augmented left ventricular (LV) mass, but preserved cardiac function, with respect to Ctrl mice. Using ECGs, heart rate variability was attenuated in MetS mice, suggesting that metabolic disorders alter cardiac sympathovagal balance. At the cellular level, LV myocytes from MetS mice had increased volume (+24%), enhanced fractional cell shortening (+42%), and faster kinetics of relaxation (-27%), with respect to Ctrl myocytes. Because cAMP and protein Kinase A (PKA) modulates myocardial contractility upon activation of G-protein coupled receptors, including beta-adrenergic receptors (B-AR), levels of these molecules were assessed by ELISA assay. Consistent with enhanced cell shortening and faster relaxation, levels of cAMP and PKA activity were, respectively, 1.8-fold and 1.9-fold larger in MetS myocytes, in comparison to Ctrl cells. Interestingly, inhibition of PKA with H-89 reduced cell shortening (-30%) and delayed kinetics of relaxation (+50%) in MetS myocytes but had no major effects on Ctrl cells. To establish the contribution of the cAMP/PKA signaling in the functional behavior of the heart with MetS, mice were treated with the B-AR blocker propranolol. Under this condition, MetS mice had reduced ejection fraction and impaired indices of diastolic function, with respect to Ctrl animals. Interestingly, myocytes obtained from Ctrl and MetS mice treated with the B-AR blocker had comparable cell shortening and kinetics of relaxation. Collectively, these results indicate that metabolic syndrome alters the functional properties of the myocytes and heart by affecting cAMP homeostasis. These properties may increase myocardial oxygen demand predisposing the heart to ischemic insults.

Exposure to four typical heavy metals induced telomere shortening of peripheral blood mononuclear cells in relevant with declined urinary aMT6s in rats

Environmental heavy metals pollution have seriously threatened the health of human beings. An increasing number of researches have demonstrated that environmental heavy metals can influence the telomere length of Peripheral Blood Mononuclear Cells (PBMCs), which implicate biological aging as well as predicts diseases. Our previous study has shown that methylmercury (MeHg)-induced telomere shortening in rat brain tissue was associated with urinary melatonin metabolite 6-sulfatoxymelatonin (aMT6s) levels. Here, we aimed to further elucidate the impact of 4 typical heavy metals (As, Hg, Cd and Pb) on telomere length of PBMCs and their association with urinary aMT6s in rats. In this study, eighty-eight male Sprague-Dawley rats were randomized grouped into eleven groups. Among them, forty 3-month-old (young) and forty 12-month-old (middle-aged) rats were divided into young or middle-aged control groups as well as typical heavy metals exposed groups, respectively. Eight 24-month-old rats (old) was divided into aging control group. The results showed that MeHg exposure in young rats while sodium arsenite (iAs), MeHg, cadmium chloride (CdCl2), lead acetate (PbAc) exposure in middle-aged rats for 3 months significantly reduced the levels of and urinary aMT6s, as well as telomere length of PBMCs. In addition, they also induced abnormalities in serum oxidative stress (SOD, MDA and GPx) and inflammatory (IL-1β, IL-6 and TNF-α) indicators. Notably, there was a significant positive correlation between declined level of urinary aMT6s and the shortening of telomere length in PBMCs in rats exposed to 4 typical heavy metals. These results suggested that 4 typical heavy metals exposure could accelerate the reduction of telomere length of PBMCs partially by inducing oxidative stress and inflammatory in rats, while ageing may be an important synergistic factor. Urinary aMT6s detection may be a alternative method to reflect telomere toxic effects induced by heavy metal exposure.

Stomatal dynamics in Alloteropsis semialata arise from the evolving interplay between photosynthetic physiology, stomatal size and biochemistry.

C4 plants are expected to have faster stomatal movements than C3 species because they tend to have smaller guard cells. However, little is known about how the evolution of C4 photosynthesis influences stomatal dynamics in relation to guard cell size and environmental factors. We studied photosynthetically diverse populations of the grass Alloteropsis semialata, showing that the origin of C4 photosynthesis in this species was associated with a shortening of stomatal guard and subsidiary cells. However, for a given cell size, C4 and C3-C4 intermediate individuals had similar or slower light-induced stomatal opening speeds than C3 individuals. Conversely, when exposed to decreasing light, stomata in C4 plants closed as fast as those in non-C4 plants. Polyploid formation in some C4 plants led to larger stomatal cells and was associated with slower stomatal opening. Conversely, diversification of C4 diploid plants into wetter environments was associated with an acceleration of stomatal opening. Overall, there was significant relationship between light-saturated photosynthesis and stomatal opening speed in the C4 plants, implying that photosynthetic energy production was limiting for stomatal opening. Stomatal dynamics in this wild grass therefore arise from the evolving interplay between photosynthetic physiology and the size and biochemical function of stomatal complexes.

The NADPH oxidase inhibitor diphenyleneiodonium suppresses Ca2+ signaling and contraction in rat cardiac myocytes.

Diphenyleneiodonium (DPI) has been widely used as an inhibitor of NADPH oxidase (Nox) to discover its function in cardiac myocytes under various stimuli. However, the effects of DPI itself on Ca2+ signaling and contraction in cardiac myocytes under control conditions have not been understood. We investigated the effects of DPI on contraction and Ca2+ signaling and their underlying mechanisms using video edge detection, confocal imaging, and whole-cell patch clamp technique in isolated rat cardiac myocytes. Application of DPI suppressed cell shortenings in a concentration-dependent manner (IC50 of ≅0.17 µM) with a maximal inhibition of ~70% at ~100 µM. DPI decreased the magnitude of Ca2+ transient and sarcoplasmic reticulum Ca2+ content by 20%-30% at 3 µM that is usually used to remove the Nox activity, with no effect on fractional release. There was no significant change in the half-decay time of Ca2+ transients by DPI. The L-type Ca2+ current (ICa) was decreased concentration-dependently by DPI (IC50 of ≅40.3 µM) with ≅13.1%-inhibition at 3 µM. The frequency of Ca2+ sparks was reduced by 3 µM DPI (by ~25%), which was resistant to a brief removal of external Ca2+ and Na+. Mitochondrial superoxide level was reduced by DPI at 3-100 µM. Our data suggest that DPI may suppress L-type Ca2+ channel and RyR, thereby attenuating Ca2+-induced Ca2+ release and contractility in cardiac myocytes, and that such DPI effects may be related to mitochondrial metabolic suppression.

Integrated remediation and detoxification of triclocarban-contaminated water using waste-derived biochar-immobilized cells by long-term column experiments

Triclocarban (TCC), an antibacterial agent commonly used in personal care products, is one of the top ten contaminants of emerging concern in various environmental media, including soil and contaminated water in vadose zone. This study aimed to investigate TCC-contaminated water remediation using biochar-immobilized bacterial cells. Pseudomonas fluorescens strain MC46 (MC46), an efficient TCC-degrading isolate, was chosen, whereas agro-industrial carbonized waste as biochar was directly used as a sustainable cell immobilization carrier. According to the long-term TCC removal performance results (160 d), the biochar-immobilized cells consistently exhibited high TCC removal efficiencies (84–97%), whereas the free MC46 removed TCC for 76–94%. At 100 days, the detachment of the MC46 cells from the immobilized cell column was observed. The micro-Fourier-transform infrared spectroscopy results indicated that extracellular polymeric substance (EPS) was produced, but polysaccharide and protein fractions were washed out of the column. The lipid fraction of EPS adhered to the biochar, promoting TCC sorption for long-term treatment. The shortening of MC46 cells improved the tolerance of TCC toxicity. The TCC-contaminated water was successfully detoxified by the biochar-immobilized MC46 cells. Overall, the waste-derived biochar-immobilized cell system proposed in this study for the removal of emerging contaminants, including TCC, is efficient, economical, and aligned with the sustainable development concept of value-added utilization of waste.

A Phytotoxin with Selective Herbicidal Activity and Related Metabolites from the Phytopathogenic Fungus Bipolaris cookei SYBL03.

Weeds are a serious threat to crop production, and the utilization of secondary metabolites of phytopathogenic fungi is considered to be an effective method of weed control. In this study, eight compounds were isolated and purified from the mycelium and fermentation broth extracts of Bipolaris cookei SYBL03. The compounds (1-8), except 2 and 6, are reported for the first time from this genus. The herbicidal activities of compounds 1-8 were studied by evaluating their effects on the seed germination and seedling growth of monocotyledonous and dicotyledonous weeds. The results indicated that compound 7 (Cyclo-N-methylphenylalanyltryptophenyl, cNMPT) exhibited a concentration-dependent dual effect on the growth of weed seedlings and selective herbicidal activity against dicotyledonous weeds. We further investigated the morphological and physiological responses of roots of Amaranthus retroflexus, a dicotyledonous weed, to compound 7. Some changes were found in seedlings grown in 400 μg/mL compound 7 solution for 96 h, such as shortening and swelling of elongation zone cells, reduced number and length of root hairs, damage and wrinkling of the root surface, occurrence of electrolyte leakage, and an increase in ethylene content. These results suggest that compound 7 may exert herbicidal activity by causing stress to weed seedlings. Increased ethylene production could be involved in the response of plants to compound 7.

Small molecule telomerase inhibitors are also potent inhibitors of telomeric C-strand synthesis.

Telomere replication is essential for continued proliferation of human cells, such as stem cells and cancer cells. Telomerase lengthens the telomeric G-strand, while C-strand replication is accomplished by CST-polymerase α-primase (CST-PP). Replication of both strands is inhibited by formation of G-quadruplex (GQ) structures in the G-rich single-stranded DNA. TMPyP4 and pyridostatin (PDS), which stabilize GQ structures in both DNA and RNA, inhibit telomerase in vitro, and in human cells they cause telomere shortening that has been attributed to telomerase inhibition. Here, we show that TMPyP4 and PDS also inhibit C-strand synthesis by stabilizing DNA secondary structures and thereby preventing CST-PP from binding to telomeric DNA. We also show that these small molecules inhibit CST-PP binding to a DNA sequence containing no consecutive guanine residues, which is unlikely to form GQs. Thus, while these "telomerase inhibitors" indeed inhibit telomerase, they are also robust inhibitors of telomeric C-strand synthesis. Furthermore, given their binding to GQ RNA and their limited specificity for GQ structures, they may disrupt many other protein-nucleic acid interactions in human cells.

Inhibition of ER stress using tauroursodeoxycholic acid rescues obesity-evoked cardiac remodeling and contractile anomalies through regulation of ferroptosis

Interrupted ER homeostasis contributes to the etiology of obesity cardiomyopathy although it remains elusive how ER stress evokes cardiac anomalies in obesity. Our study evaluated the impact of ER stress inhibition on cardiac anomalies in obesity. Lean and ob/ob obese mice received chemical ER chaperone tauroursodeoxycholic acid (TUDCA, 50 mg/kg/d, p.o.) for 35 days prior to evaluation of glucose sensitivity, echocardiographic, myocardial geometric, cardiomyocyte mechanical and subcellular Ca2+ property, mitochondrial integrity, oxidative stress, apoptosis, and ferroptosis. Intracellular Ca2+ governing domains including sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) were monitored by45Ca2+uptake and immunoblotting. Our results noted that TUDCA alleviated myocardial remodeling (fibrosis, hypertrophy, enlarged LVESD), echocardiographic anomalies (compromised fractional shortening and ejection fraction), cardiomyocyte contractile dysfunction (amplitude and velocity of cell shortening, relengthening time) and intracellular Ca2+ anomalies (compromised subcellular Ca2+ release, clearance and SERCA function), mitochondrial damage (collapsed membrane potential, downregulated mitochondrial elements and ultrastructural alteration), ER stress (GRP78, eIF2α and ATF4), oxidative stress, apoptosis and ferroptosis [downregulated SLC7A11, GPx4 and upregulated transferrin receptor (TFRC)] without affecting global glucose sensitivity and serum Fe2+ in obese mice. Obesity-evoked change in HSP90, phospholamban and Na+-Ca2+ exchanger was spared by the chemical ER chaperone. Moreover, in vitro results noted that TUDCA, PERK inhibitor GSK2606414, TFRC neutralizing antibody and ferroptosis inhibitor LIP1 mitigated palmitic acid-elicited changes in lipid peroxidation and mechanical function. Our findings favored a role for ferroptosis in obesity cardiomyopathy downstream of ER stress.

Cardioprotective effect of the anti-ageing protein Klotho on ischemic heart disease

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): ISCIII, Ministerio de Universidades, Education and Research Council of Madrid, Biomedicine Network Comunidad de Madrid Background Cardiovascular diseases are the leading cause of death and disability worldwide. Among them, ischemic heart disease, due to myocardial infarction (MI) remains the first cause of cardiovascular death. The anti-ageing protein Klotho is mainly expressed in membrane at renal level. However, Klotho also has a soluble form with different pleiotropic functions that are still undetermined, including a possible cardioprotective role that is currently the target of several studies. Purpose Firstly, we evaluated circulating Klotho levels related to cardiac damage in a cohort of 146 patients after ST-elevation myocardial infarction (STEMI) and in an experimental post-myocardial infarction (PMI) model. Secondly, we investigated soluble Klotho supplementation as a potential novel therapeutic strategy for the prevention of cardiac dysfunction, deleterious remodeling, cardiomyocyte calcium (Ca2+) mishandling and arrhythmias in PMI mice. Methods Study with human samples: we analysed Klotho and NT-proBNP plasma levels in STEMIpatients with preserved renal function. Experimental study: C57BL6 mice subjected to PMI by ligation of the left anterior descending coronary artery were treated with vehicle solution or recombinant Klotho (10 mg/Kg/day) for 15 days after MI. Cardiac function was studied through non-invasive methods including electrocardiogram (ECG) and cardiac magnetic resonance imaging (CMRI). Intracellular Ca2+ handling was analysed using confocal microscopy in isolated ventricular cardiomyocytes. Cardiac remodeling was studied through histological and biomolecular analysis of several markers of cardiac damage and target proteins involved in Ca2+ handling. Results Plasma Klotho levels decrease rapidly after MI in both STEMI patients and PMI mice. Additionally, MI patients in the lowest Klotho tertile showed significantly elevated NT-proBNP levels. Klotho treatment decreased the infarct area in PMI mice accompanied by a decrease in both cardiac hypertrophy and fibrosis. Moreover, reduction in ejection fraction and MI-related ECG alterations were reduced in PMI mice treated with Klotho, including increased QRS, JT, QTc intervals and occurrence of premature ventricular contractions. Klotho also prevented systolic Ca2+ release and cell shortening disturbances in cardiomyocytes from PMI mice without Klotho. Increased diastolic Ca2+ leak was prevented in mice treated with Klotho via CaMKII-dependent pathway by avoiding its phosphorylation and the RyR2 phosphorylation at CaMKII site. Conclusions Klotho supplementation protect against MI by avoiding deleterious cardiac remodeling and ameliorating one of the main complications of MI such as arrhythmias. Thus, recombinant Klotho prevents the intracardiomyocyte Ca2+ mishandling after MI. Our translational findings support the importance of Klotho as a novel biomarker of ventricular damage just after MI and as a novel therapeutic strategy for prevention cardiac events associated to ischemic heart disease.

Cardiac function is regulated by the sodium-dependent inhibition of the sodium-calcium exchanger NCX1

The Na+-Ca2+ exchanger (NCX1) is the dominant Ca2+ extrusion mechanism in cardiac myocytes. NCX1 activity is inhibited by intracellular Na+ via a process known as Na+-dependent inactivation. A central question is whether this inactivation plays a physiological role in heart function. Using CRISPR/Cas9, we inserted the K229Q mutation in the gene (Slc8a1) encoding for NCX1. This mutation removes the Na+-dependent inactivation while preserving transport properties and other allosteric regulations. NCX1 mRNA levels, protein expression, and protein localization are unchanged in K229Q male mice. However, they exhibit reduced left ventricular ejection fraction and fractional shortening, while displaying a prolonged QT interval. K229Q ventricular myocytes show enhanced NCX1 activity, resulting in action potential prolongation, higher incidence of aberrant action potentials, a faster decline of Ca2+ transients, and depressed cell shortening. The results demonstrate that NCX1 Na+-dependent inactivation plays an essential role in heart function by affecting both cardiac excitability and contractility.

Combined approach of selective and accelerated cloning for microfluidic chip-based system increases clone specific productivity.

Improving current cell line development workflows can either focus on increasing the specific productivity of the cell lines or shortening timelines to reach the clinic as fast as possible. In this work, using the Beacon platform, we have combined two distinct protocols - early cloning with low-viability pools, and IgG membrane staining-, to concomitantly reach both objectives, and generate highly productive CHO clones in shorter timelines. Fast-sorting approaches using low-viability pools in combination with the Beacon platform have recently been reported to shorten CLD timelines. However, the low recovery led to a drastic reduction in the clone number obtained postcloning. Here, we report a combined approach of fast-sorting and fluorescent membrane staining. With this new protocol, the cells reach a correct recovery, allowing to fully exploit the Beacon screening capacities. In addition, by using a fluorescent staining recognizing the secreted IgG, we were able to enrich the fraction of highly secreting cells prior to cloning and we obtained significant increases in the cell's specific productivity. The combination of these two protocols has a synergistic effect, and as they help discarding the dead and nonproducing populations prior to cloning, they increase the throughput power of the Beacon platform and the detection of super productive clones.

Novel protective effect of the FOXO3 longevity genotype on mechanisms of cellular aging in Okinawans

The genetic association of FOXO3 genotypes with human longevity is well established, although the mechanism is not fully understood. We now report on the relationship of the FOXO3 longevity variant rs2802292 with telomere length, telomerase activity, FOXO3 expression, and inflammatory cytokine levels in men and women. In agreement with earlier work, the FOXO3 longevity variant conferred protection against telomere shortening of peripheral blood mononuclear cells from adults aged 55 years and older. This was accompanied by higher levels of telomerase activity in mononuclear cells for carriers of the longevity-associated FOXO3 G-allele of SNP rs2802292 (P = 0.015). FOXO3 mRNA expression increased slightly with age in both young (P = 0.02) and old (P = 0.08) G-allele carriers. Older female G-allele carriers displayed a modest decline in levels of pro-inflammatory cytokine IL-6 with age (P = 0.07). In contrast, older male G-allele carriers displayed an age-dependent increase in levels of anti-inflammatory cytokine IL-10 with age (P = 0.04). Thus, FOXO3 may act through several different pro-longevity mechanisms, which may differ by age and sex.

Discovery of a selective TRF2 inhibitor FKB04 induced telomere shortening and senescence in liver cancer cells.

Telomere repeat binding factor 2 (TRF2), a critical element of the shelterin complex, plays a vital role in the maintenance of genome integrity. TRF2 overexpression is found in a wide range of malignant cancers, whereas its down-regulation could cause cell death. Despite its potential role, the selectively small-molecule inhibitors of TRF2 and its therapeutic effects on liver cancer remain largely unknown. Our clinical data combined with bioinformatic analysis demonstrated that TRF2 is overexpressed in liver cancer and that high expression is associated with poor prognosis. Flavokavain B derivative FKB04 potently inhibited TRF2 expression in liver cancer cells while having limited effects on the other five shelterin subunits. Moreover, FKB04 treatment induced telomere shortening and increased the amounts of telomere-free ends, leading to the destruction of T-loop structure. Consequently, FKB04 promoted liver cancer cell senescence without modulating apoptosis levels. In corroboration with these findings, FKB04 inhibited tumor cell growth by promoting telomeric TRF2 deficiency-induced telomere shortening in a mouse xenograft tumor model, with no obvious side effects. These results demonstrate that TRF2 is a potential therapeutic target for liver cancer and suggest that FKB04 may be a selective small-molecule inhibitor of TRF2, showing promise in the treatment of liver cancer.

Disruption of mitochondrial unfolded protein response results in telomere shortening in mouse oocytes and somatic cells.

Caseinolytic peptidase P (CLPP) plays a central role in mitochondrial unfolded protein response (mtUPR) by promoting the breakdown of misfolded proteins and setting in motion a cascade of reactions to re-establish protein homeostasis. Global germline deletion of Clpp in mice results in female infertility and accelerated follicular depletion. Telomeres are tandem repeats of 5'-TTAGGG-3' sequences found at the ends of the chromosomes. Telomeres are essential for maintaining chromosome stability during somatic cell division and their shortening is associated with cellular senescence and aging. In this study, we asked whether the infertility and ovarian aging phenotype caused by global germline deletion of Clpp is associated with somatic aging, and tested telomere length in tissues of young and aging mice. We found that impaired mtUPR caused by the lack of CLPP is associated with accelerated telomere shortening in both oocytes and somatic cells of aging mice. In addition, expression of several genes that maintain telomere integrity was decreased, and double-strand DNA breaks were increased in telomeric regions. Our results highlight how impaired mtUPR can affect telomere integrity and demonstrate a link between loss of mitochondrial protein hemostasis, infertility, and somatic aging.

Role of protein kinase D1 in vasoconstriction and haemodynamics in rats

AimsProtein kinase D (PKD), once considered an effector of protein kinase C (PKC), now plays many pathophysiological roles in various tissues. However, little is known about role of PKD in vascular function. We investigated the role of PKD in contraction of rat aorta and human aortic smooth muscle cells (HASMCs) and in haemodynamics in rats. Methods and resultsIsometric tension of rat aortic was measured to examine norepinephrine-induced contraction in the presence of PKD, PKC and Rho-kinase inhibitors. Phosphorylation of PKD1, myosin targeting subunit-1 (MYPT1), myosin light chain (MLC), CPI-17 and heat-shock protein 27 (HSP27), and actin polymerization were measured in the aorta. Phosphorylation of MYPT1 and MLC was also measured in HASMCs knocked down with specific siRNAs of PKD 1, 2 and 3. Intracellular calcium concentrations and cell shortening were measured in HASMCs.Norepinephrine-induced aortic contraction was accompanied by increased phosphorylation of PKD1, MYPT1 and MLC and actin polymerization, all of which were attenuated with PKD inhibitor CRT0066101. PKD1 phosphorylation was not inhibited by PKC inhibitor, chelerythrine or Rho kinase inhibitor, fasudil. In HASMCs, the phosphorylation of MYPT1 and MLC was attenuated by PKD1, but not PKD2, 3 knockdown. In HASMCs, CRT0066101 inhibited norepinephrine-induced cell shortening without affecting calcium concentration. Administration of CRT0066101 decreased systemic vascular resistance and blood pressure without affecting cardiac output in rats. ConclusionsPKD1 may play roles in aorta contraction and haemodynamics via phosphorylation of MYPT1 and actin polymerization in a calcium-independent manner.