TRPM7 transactivates the FOSL1 gene through STAT3 and enhances glioma stemness

INTRODUCTION

We previously reported that TRPM7 regulates glioma cells' stemness through STAT3. In addition, we demonstrated that FOSL1 is a response gene for TRPM7, and the FOSL1 gene serves as an oncogene to promote glioma proliferation and invasion.

METHODS

In the present study, we determined the effects of FOSL1 on glioma stem cell (GSC) markers CD133 and ALDH1 by flow cytometry, and the maintenance of stem cell activity by extreme limiting dilution assays (ELDA). To further gain insight into the mechanism by which TRPM7 activates transcription of the FOSL1 gene to contribute to glioma stemness, we constructed a FOSL1 promoter and its GAS mutants followed by luciferase reporter assays and ChIP-qPCR in a glioma cell line and glioma patient-derived xenoline. We further examined GSC markers ALDH1 and TRPM7 as well as FOSL1 by immunohistochemistry staining (IHC) in brain tissue microarray (TMA) of glioma patients.

RESULTS

We revealed that FOSL1 knockdown reduces the expression of GSC markers CD133 and ALDH1, and FOSL1 is required to maintain stem cell activity in glioma cells. The experiments also showed that mutations of - 328 to - 336 and - 378 to - 386 GAS elements markedly reduced FOSL1 promoter activity. Constitutively active STAT3 increased while dominant-negative STAT3 decreased FOSL1 promoter activity. Furthermore, overexpression of TRPM7 enhanced while silencing of TRPM7 reduced FOSL1 promoter activity. ChIP-qPCR assays revealed that STAT3, present in nuclear lysates of glioma cells stimulated by constitutively activated STAT3, can bind to two GAS elements, respectively. We demonstrated that deacetylation of FOSL1 at the Lys-116 residue located within its DNA binding domain led to an increase in FOSL1 transcriptional activity. We found that the expression of TRPM7, ALDH1, and FOSL1 protein is associated with grades of malignant glioma, and TRPM7 protein expression correlates to the expression of ALDH1 and FOSL1 in glioma patients.

CONCLUSIONS

These combined results demonstrated that TRPM7 induced FOSL1 transcriptional activation, which is mediated by the action of STAT3, a mechanism shown to be important in glioma stemness. These results indicated that FOSL1, similar to GSC markers ALDH1 and TRPM7, is a diagnostic marker and potential drug target for glioma patients.

Non-rapid eye movement sleep determines resilience to social stress

Resilience, the ability to overcome stressful conditions, is found in most mammals and varies significantly among individuals. A lack of resilience can lead to the development of neuropsychiatric and sleep disorders, often within the same individual. Despite extensive research into the brain mechanisms causing maladaptive behavioral-responses to stress, it is not clear why some individuals exhibit resilience. To examine if sleep has a determinative role in maladaptive behavioral-response to social stress, we investigated individual variations in resilience using a social-defeat model for male mice. Our results reveal a direct, causal relationship between sleep amount and resilience-demonstrating that sleep increases after social-defeat stress only occur in resilient mice. Further, we found that within the prefrontal cortex, a regulator of maladaptive responses to stress, pre-existing differences in sleep regulation predict resilience. Overall, these results demonstrate that increased NREM sleep, mediated cortically, is an active response to social-defeat stress that plays a determinative role in promoting resilience. They also show that differences in resilience are strongly correlated with inter-individual variability in sleep regulation.

TRPM7 Induces Tumorigenesis and Stemness Through Notch Activation in Glioma

We have reported that transient receptor potential melastatin-related 7 (TRPM7) regulates glioma stem cells (GSC) growth and proliferation through Notch, STAT3-ALDH1, and CD133 signaling pathways. In this study, we determined the major contributor(s) to TRPM7 mediated glioma stemness by further deciphering each individual Notch signaling. We first determined whether TRPM7 is an oncotarget in glioblastoma multiforme (GBM) using the Oncomine database. Next, we determined whether TRPM7 silencing by siRNA TRPM7 (siTRPM7) induces cell growth arrest or apoptosis to reduce glioma cell proliferation using cell cycle analysis and annexin V staining assay. We then examined the correlations between the expression of TRPM7 and Notch signaling activity as well as the expression of GSC markers CD133 and ALDH1 in GBM by downregulating TRPM7 through siTRPM7 or upregulating TRPM7 through overexpression of human TRPM7 (M7-wt). To distinguish the different function of channel and kinase domain of TRPM7, we further determined how the α-kinase-dead mutants of TRPM7 (α-kinase domain deleted/M7-DK and K1648R point mutation/M7-KR) affect Notch activities and CD133 and ALDH1 expression. Lastly, we determined the changes in TRPM7-mediated regulation of glioma cell growth/proliferation, cell cycle, and apoptosis by targeting Notch1. The Oncomine data revealed a significant increase in TRPM7 mRNA expression in anaplastic astrocytoma, diffuse astrocytoma, and GBM patients compared to that in normal brain tissues. TRPM7 silencing reduced glioma cell growth by inhibiting cell entry into S and G2/M phases and promoting cell apoptosis. TRPM7 expression in GBM cells was found to be positively correlated with Notch1 signaling activity and CD133 and ALDH1 expression; briefly, downregulation of TRPM7 by siTRPM7 decreased Notch1 signaling whereas upregulation of TRPM7 increased Notch1 signaling. Interestingly, kinase-inactive mutants (M7-DK and M7-KR) resulted in reduced activation of Notch1 signaling and decreased expression of CD133 and ALDH1 compared to that of wtTRPM7. Finally, targeting Notch1 effectively suppressed TRPM7-induced growth and proliferation of glioma cells through cell G1/S arrest and apoptotic induction. TRPM7 is responsible for sustained Notch1 signaling activation, enhanced expression of GSC markers CD133 and ALDH1, and regulation of glioma stemness, which contributes to malignant glioma cell growth and invasion.

Bioactive nanoparticles improve calcium handling in failing cardiac myocytes

AIMS

To evaluate the ability of N-acetylglucosamine (GlcNAc) decorated nanoparticles and their cargo to modulate calcium handling in failing cardiac myocytes (CMs).

MATERIALS & METHODS

Primary CMs isolated from normal and failing hearts were treated with GlcNAc nanoparticles in order to assess the ability of the nanoparticles and their cargo to correct dysfunctional calcium handling in failing myocytes.

RESULTS & CONCLUSION

GlcNAc particles reduced aberrant calcium release in failing CMs and restored sarcomere function. Additionally, encapsulation of a small calcium-modulating protein, S100A1, in GlcNAc nanoparticles also showed improved calcium regulation. Thus, the development of our bioactive nanoparticle allows for a 'two-hit' treatment, by which the cargo and also the nanoparticle itself can modulate intracellular protein activity.

Purification of cardiomyocytes from differentiating pluripotent stem cells using molecular beacons that target cardiomyocyte-specific mRNA

BACKGROUND

Although methods for generating cardiomyocytes from pluripotent stem cells have been reported, current methods produce heterogeneous mixtures of cardiomyocytes and noncardiomyocyte cells. Here, we report an entirely novel system in which pluripotent stem cell-derived cardiomyocytes are purified by cardiomyocyte-specific molecular beacons (MBs). MBs are nanoscale probes that emit a fluorescence signal when hybridized to target mRNAs.

METHOD AND RESULTS

Five MBs targeting mRNAs of either cardiac troponin T or myosin heavy chain 6/7 were generated. Among 5 MBs, an MB that targeted myosin heavy chain 6/7 mRNA (MHC1-MB) identified up to 99% of HL-1 cardiomyocytes, a mouse cardiomyocyte cell line, but <3% of 4 noncardiomyocyte cell types in flow cytometry analysis, which indicates that MHC1-MB is specific for identifying cardiomyocytes. We delivered MHC1-MB into cardiomyogenically differentiated pluripotent stem cells through nucleofection. The detection rate of cardiomyocytes was similar to the percentages of cardiac troponin T- or cardiac troponin I-positive cardiomyocytes, which supports the specificity of MBs. Finally, MHC1-MB-positive cells were sorted by fluorescence-activated cell sorter from mouse and human pluripotent stem cell differentiating cultures, and ≈97% cells expressed cardiac troponin T or cardiac troponin I as determined by flow cytometry. These MB-based sorted cells maintained their cardiomyocyte characteristics, which was verified by spontaneous beating, electrophysiological studies, and expression of cardiac proteins. When transplanted in a myocardial infarction model, MB-based purified cardiomyocytes improved cardiac function and demonstrated significant engraftment for 4 weeks without forming tumors.

CONCLUSIONS

We developed a novel cardiomyocyte selection system that allows production of highly purified cardiomyocytes. These purified cardiomyocytes and this system can be valuable for cell therapy and drug discovery.

Abstract 150: Determining Changes in Contractility, Myofilament Expression and Myofilament Sensitivity in the Developing Human Ventricle

As pediatric cardiac surgery is increasingly performed in the first year of life, the need for understanding contractility regulation becomes increasingly important. We examined contractility and myofilament changes in ventricular biopsies removed as part of the surgical correction of congenital heart defects from newborns (NB) (hypoplastic left heart syndrome, < 1 wk old) and infants (IF) (tetralogy of Fallot, 3-12 mo old). Sarcomere shortening and calcium (Ca) transients were measured in isolated ventricular cells stimulated at 0.5 and 1 Hz. Increasing pacing frequency caused a significant increase in sarcomere shortening (p< 0.05)in only the IF, but the Ca transient amplitude was relatively unchanged in both groups. Consistent with work in the developing rat heart, we found an isoform switch with increasing developmental age in myofilament proteins, troponin T (TnT) and troponin I (TnI). Western blot analysis revealed that total TnI (the sum of cardiac TnI (cTnI) and slow skeletal TnI (ssTnI)) was not significantly different between the two age groups. However, when comparing only the cTnI isoforms, we found that the NB had a significantly lower levels compared to the IF (11556±789 a.u. vs. 21770±1700 a.u., p<0.001). Analysis of the RT-PCR revealed nearly significant lower levels of TnT isoform 1 in the IF group than the NB group (p=0.078), no significant difference in the levels of TnT isoform 2 (p= 0.536), and significantly higher levels of TnT isoform 3 in the IF group than the NB group (p= 0.039). We also observed developmental changes in myofilament sensitivity to calcium as assessed by measuring the gradient of the fura-2 cell length trajectory on phase-plane diagrams during the late relaxation of the twitch contraction. These results collectively suggest that contractility and myofilament changes, or the lack of changes, may serve as targets for clarifying elements associated with cardiac dysfunction in the developing human ventricle.

Abstract 143: Catalase, Oxidative Stress and Ischemic Injury: Role of c-Abl Tyrosine Kinase

Thousands of children with congenital heart disease are subjected to corrective surgery which involves stopping the heart and exposing it to ischemia reperfusion (IR) injury. Complications after cardiopulmonary bypass like low cardiac output can lead to inadequate organ perfusion and eventual organ dysfunction if not corrected in a timely manner. Newborn (2-4 days) hearts are more susceptible to ischemic injury than adult (>8 weeks) hearts as evidenced by their diminished ability to scavenge reactive oxygen species (ROS), specifically hydrogen peroxide (H 2 O 2 ). Not only do newborn hearts exhibit decreased scavenging capability (compared to the adult) but they also contain reduced baseline levels of catalase (3.8 + 1.1 U/mg tissue in the LV and 4.3 + 2.3 U/mg tissue in the RV vs. 11.2 + 1.0 U/mg tissue in the adult LV and 11.6 + 0.3 U/mg tissue in the adult RV). We observed significantly increased levels of H 2 O 2 in newborn rabbit myocytes following IR injury (4.3-fold vs 2.2 fold; p<0.05) that was not accompanied by an increase in catalase activity as was seen in the adult myocytes. The tyrosine kinase c-Abl was shown to play a role in regulating phosphyorylation (and activation) of catalase and we hypothesized this pathway may be dysregulated in newborns, leading to differences in catalase activity. We performed immunoprecipitation with c-Abl and catalase as well as Western analysis of whole heart homogenates in both newborn and adult samples (n=3). Results demonstrated an increase in catalase phosphorylation in adult but not newborn hearts after IR. In the newborn, preliminary studies displayed diminished phosphorylation of c-Abl, indicating a potential mechanism. In addition, catalase levels seem to acutely rise following IR, too early for new protein synthesis. Catalase is known to undergo ubiquitination following release from the c-Abl complex and this may play a role in the failure of newborns to increase catalase. Elucidation of this pathway will lead to a greater understanding of the mechanisms controlling catalase activity in the newborn versus the adult heart and will prove beneficial in developing therapeutic interventions to minimize damage following ischemic injury in newborns.

Abstract 154: Generation of Purified Cardiomyocytes from Pluripotent Stem Cells Using Molecular Beacons

Background: While various methods for generating cardiomyocytes (CMs) from pluripotent stem cells (PSCs) including both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have been reported, all available methods are only allowed to produce heterogeneous population of CM mixed with non-CM cells. Therefore, strategies to enrich pure CMs for scientific and clinical applications have been highly required. Hence, we developed a novel system in which CMs can be purified by cardiac specific molecular beacons (MBs). MBs are dual-labeled antisense nano-scale probes that emit a fluorescence signal when hybridized to target mRNAs. We hypothesized that MBs targeted to CM specific mRNAs can identify CMs and allow isolation of purified CMs by fluorescence-activated cell sorting (FACS).

Methods and results: Five MBs targeting distinct sites on either cardiac troponin T (cTNT) or α/β myosin heavy chain (α/βMHC) were designed and characterized in various cell types. To find the optimal MB that can selectively identifying CMs, each MB was delivered into HL-1 CMs, an immortalized mouse CM cell line, smooth muscle cells, endothelial cells, mouse ESCs and fibroblasts and its specificity was determined by flow cytometry. As a result, two MBs identified MB+ cells up to 98% from HL-1 CMs but lower than 10% of the non-CM cells suggesting these MBs are CM specific. Subsequently, the selected MBs were delivered into both mouse and human PSCs derived CMs and 41 to 49% of the cells were identified as an MB+ population. Interestingly, the rate of MB+ cells was similar to CM quantification determined by cTNT intracellular flow cytometry. Finally, we determined whether cell sorting with cardiac-specific MBs can enrich CMs from the heterogeneous mouse and human PSC cultures and found that ∼97% of MB-based sorted CMs expressed cTNT. These enriched cells were further cultured and their CM identity was verified by immunocytochemistry and qRT-PCR analysis. Ca2+ transient analysis further confirmed that these purified CMs displayed functional CM characteristics

Conclusion: Using cardiac specific MBs, we were able to obtain highly purified CMs. These purified CMs and the system can be highly useful for clinical applications as well as drug discovery.

Abstract 69: Diminished T-Tubule Density in Newborn Human Ventricular Cells Is Associated with Heterogeneity of Calcium Transients

For children with congenital heart disease (CHD), therapies developed for adults may have different effects on immature myocardium. Thus, it is critical to understand calcium handling in the young human ventricle.

Methods: Human ventricular cells were isolated from tissue removed as part of the surgical repair for CHDs from two age groups: newborns (<1 week old) and infants (2-12 months old). Developmental changes in t-tubules were examined in live cells with Di-8 ANEPPS which highlights the cell membrane. We measured the T-index (percent of cell interior occupied by t-tubules), averaged for at least 3 confocal z-sections per cell. Changes in calcium transients were measured by confocal line scans in cells loaded with Fluo-4 and field stimulated (37°C).

Results: Newborn human myocytes have very few t-tubules whereas infant myocytes have a range of t-tubule densities. The T-index in newborn myocytes was significantly less than in infant myocytes (4.4±0.2%, n=8 cells, 3 newborns vs. 9.1±0.9%, n=55 cells, 7 infants). Furthermore, there was sizable heterogeneity in the T-index for each patient in the infant group, in which some cells had few t-tubules and others had many t-tubules. We calculated the coefficient of variation (CV=SD/mean*100) for each patient and compared CV values for newborns vs. infants. CV was significantly greater in infants compared to newborns (46.5±7.4%, n=7, vs. 9.4±1.9%, n=3, p<0.02). In addition, calcium transients from newborn cells had a ‘U’ shaped wavefront with calcium first increasing at the outer edge of the cell then propagating toward the center. In contrast, infant cells had a homogenous calcium wavefront. The delay of peak calcium from the edge to center was significantly longer in newborns compared to infants (61.7±8.9 ms, n=8 cells, 3 newborns vs. 10.6±1.6 ms, n=6 cells, 4 infants, p<0.001).

Conclusions: There are heterogeneous calcium transients in newborn human myocytes that correspond to a lack of t-tubules. Furthermore, t-tubule development occurs in a heterogeneous manner throughout the first year of life with cells from the same patient exhibiting different degrees of t-tubule development. This is the first study to examine t-tubule development and calcium transients in the very young human ventricular myocardium.

Abstract P322: Chamber-Specific Differences in Oxidative Stress in Newborn Versus Adult Rabbit Hearts Following Ischemia-Reperfusion

Each year, tens of thousands of children undergo cardiopulmonary bypass (CPB) to correct congenital heart defects. While necessary for surgery, CPB involves stopping the heart and exposing it to ischemic conditions. While much is known about adult injury, little is known about the effects of global ischemia on newborn ventricles. The purpose of this study was to determine age- and chamber-specific differences in oxidative stress following global ischemia-reperfusion injury. We studied newborn (2–4 days) and adult (>8 weeks) rabbit hearts subjected to Langendorff ischemia-reperfusion (30 minutes ischemia, 60 minutes reperfusion). Catalase and superoxide dismutase (SOD) activities were measured, as well as real-time hydrogen peroxide (H 2 O 2 ) and superoxide (O 2 − ) generation using confocal microscopy in isolated left and right ventricular (LV and RV) myocytes exposed to hypoxia. Our data demonstrate chamber and age-specific changes in oxidative stress. During ischemia, H 2 O 2 increased significantly in the RV while remaining constant in the LV of newborn rat rabbit myocytes. In contrast, there was a smaller, nonsignificant increase in H 2 O 2 in both both RV and LV myocytes of adults. The increase seen in the RV of newborns was several fold higher than that of adults (4.3-fold vs. 2.2 fold; p<0.05). In whole heart tissue, catalase activity was significantly increased following ischemia in both adult ventricles, while no increase was seen in newborn hearts compared to sham hearts. Additionally, levels in newborns were several fold lower (p<0.05), indicating less scavenging potential. SOD activity was increased from sham vs. ischemia in the LV of both adult and newborn hearts, but only in the RV of the newborn heart (0.80±0.09 to 3.0±0.43 U/mg; p<0.001). Intra-cardiac injection of an H 2 O 2 scavenger, Ebselen, loaded in nanoparticles, improved recovery of developed pressure (49.53±16.25 to 80.0±11.31) in the RV of the newborn (p<0.05), suggesting the local delivery of an exogenous antioxidant is cardioprotective in newborn RVs. Our data demonstrate there are ventricle-specific differences in oxidative stress between newborn and adult rabbit hearts. Local therapy is able to address some of these differences and may limit damage during bypass surgery.