Stroma cell-derived factor-1α signaling enhances calcium transients and beating frequency in rat neonatal cardiomyocytes

Mitochondrial calcium homeostasis in hematopoietic stem cell: Molecular regulation of quiescence, function, and differentiation

Hematopoiesis is based on the existence of hematopoietic stem cells (HSC) with the capacity to self-proliferate and self-renew or to differentiate into specialized cells. The hematopoietic niche is the essential microenvironment where stem cells reside and integrate various stimuli to determine their fate. Recent studies have identified niche containing high level of calcium (Ca²⁺) suggesting that HSCs are sensitive to Ca²⁺. This is a highly versatile and ubiquitous second messenger that regulates a wide variety of cellular functions. Advanced methods for measuring its concentrations, genetic experiments, cell fate tracing data, single-cell imaging, and transcriptomics studies provide information into its specific roles to integrate signaling into an array of mechanisms that determine HSC identity, lineage potential, maintenance, and self-renewal. Accumulating and contrasting evidence, are revealing Ca²⁺ as a previously unacknowledged feature of HSC, involved in functional maintenance, by regulating multiple actors including transcription and epigenetic factors, Ca²⁺-dependent kinases and mitochondrial physiology. Mitochondria are significant participants in HSC functions and their responsiveness to cellular demands is controlled to a significant extent via Ca²⁺ signals. Recent reports indicate that mitochondrial Ca²⁺ uptake also controls HSC fate. These observations reveal a physiological feature of hematopoietic stem cells that can be harnessed to improve HSC-related disease. In this review, we discuss the current knowledge Ca²⁺ in hematopoietic stem cell focusing on its potential involvement in proliferation, self-renewal and maintenance of HSC and discuss future research directions.

An improved two-step method for extraction and purification of primary cardiomyocytes from neonatal mice

INTRODUCTION

Primary mouse cardiomyocytes are essential tools for cardiovascular pharmacology research at the cellular and molecular levels, but their low viability and low purity have often caused challenges in previous studies. Hence, we developed an improved two-step method for extraction and purification of primary cardiomyocytes from neonatal mice.

METHOD

This method consisted of two steps: 1) isolation and pre-digestion of heart tissues from 1- to 3-day-old C57 neonatal mice and 2) extraction and purification of cardiomyocytes. The traditional method of primary mouse cardiomyocyte isolation was used as the control group to assess the extraction efficiency of cardiomyocytes by the two-step method, and the purity and viability of cardiomyocytes were evaluated by immunofluorescence staining and autonomous beating analysis, respectively.

RESULTS

Compared with the control method, the two-step method enabled acquisition of more cells from mouse hearts (1.28 ± 0.11 × 10⁶vs 0.59 ± 0.15 × 10⁶ cells/heart), and the resulting cells exhibited higher adherence rates and cell purity (93.25 ± 1.69% vs 73.62 ± 9.76%) after 48 h of culture. Moreover, the viability of cardiomyocytes was also evidently higher in the two-step group than in the control group (124.67 ± 10.50 vs 88.50 ± 6.61 beats/min).

DISCUSSION

Compared with the traditional method, the two-step method exhibited significantly better efficiency in extraction of primary cardiomyocytes and yielded cells with greater purity and viability. The two-step method will likely become a standard method for studies based on primary mouse cardiomyocytes in the future.

hERG K+ Channels Promote Survival of Irradiated Leukemia Cells

Many tumor cells express highly elevated activities of voltage-gated K⁺ channels in the plasma membrane which are indispensable for tumor growth. To test for K⁺ channel function during DNA damage response, we subjected human chronic myeloid leukemia (CML) cells to sub-lethal doses of ionizing radiation (0-8 Gy, 6 MV photons) and determined K⁺ channel activity, K⁺ channel-dependent Ca²⁺ signaling, cell cycle progression, DNA repair, and clonogenic survival by whole-cell patch clamp recording, fura-2 Ca²⁺ imaging, Western blotting, flow cytometry, immunofluorescence microscopy, and pre-plating colony formation assay, respectively. As a result, the human erythroid CML cell line K562 and primary human CML cells functionally expressed hERG1. Irradiation stimulated in both cell types an increase in the activity of hERG1 K⁺ channels which became apparent 1-2 h post-irradiation. This increase in K⁺ channel activity was paralleled by an accumulation in S phase of cell cycle followed by a G₂/M cell cycle arrest as analyzed between 8 and 72 h post-irradiation. Attenuating the K⁺ channel function by applying the hERG1 channel inhibitor E4031 modulated Ca²⁺ signaling, impaired inhibition of the mitosis promoting subunit cdc2, overrode cell cycle arrest, and decreased clonogenic survival of the irradiated cells but did not affect repair of DNA double strand breaks suggesting a critical role of the hERG1 K⁺ channels for the Ca²⁺ signaling and the cell cycle control during DNA damage response.

Crosstalk between lysine methylation and phosphorylation of ATG16L1 dictates the apoptosis of hypoxia/reoxygenation-induced cardiomyocytes

Post-translational modifications of autophagy-related (ATG) genes are necessary to modulate their functions. However, ATG protein methylation and its physiological role have not yet been elucidated. The methylation of non-histone proteins by SETD7, a SET domain-containing lysine methyltransferase, is a novel regulatory mechanism to control cell protein function in response to various cellular stresses. Here we present evidence that the precise activity of ATG16L1 protein in hypoxia/reoxygenation (H/R)-treated cardiomyocytes is regulated by a balanced methylation and phosphorylation switch. We first show that H/R promotes autophagy and decreases SETD7 expression, whereas autophagy inhibition by 3-MA increases SETD7 level in cardiomyocytes, implying a tight correlation between autophagy and SETD7. Then we demonstrate that SETD7 methylates ATG16L1 at lysine 151 while KDM1A/LSD1 (lysine demethylase 1A) removes this methyl mark. Furthermore, we validate that this methylation at lysine 151 impairs the binding of ATG16L1 to the ATG12-ATG5 conjugate, leading to inhibition of autophagy and increased apoptosis in H/R-treated cardiomyocytes. However, the cardiomyocytes with shRNA-knocked down SETD7 or inhibition of SETD7 activity by a small molecule chemical, display increased autophagy and decreased apoptosis following H/R treatment. Additionally, methylation at lysine 151 inhibits phosphorylation of ATG16L1 at S139 by CSNK2 which was previously shown to be critical for autophagy maintenance, and vice versa. Together, our findings define a novel modification of ATG16L1 and highlight the importance of an ATG16L1 phosphorylation-methylation switch in determining the fate of H/R-treated cardiomyocytes.

Small molecules for reprogramming and transdifferentiation

Pluripotency reprogramming and transdifferentiation induced by transcription factors can generate induced pluripotent stem cells, adult stem cells or specialized cells. However, the induction efficiency and the reintroduction of exogenous genes limit their translation into clinical applications. Small molecules that target signaling pathways, epigenetic modifications, or metabolic processes can regulate cell development, cell fate, and function. In the recent decade, small molecules have been widely used in reprogramming and transdifferentiation fields, which can promote the induction efficiency, replace exogenous genes, or even induce cell fate conversion alone. Small molecules are expected as novel approaches to generate new cells from somatic cells in vitro and in vivo. Here, we will discuss the recent progress, new insights, and future challenges about the use of small molecules in cell fate conversion.

The human bitter taste receptor T2R38 is broadly tuned for bacterial compounds

T2R38 has been shown to be a specific bacterial detector implicated in innate immune defense mechanism of human upper airway. Several clinical studies have demonstrated that this receptor is associated with the development of chronic rhinosinusitis (CRS). T2R38 was previously reported to bind to homoserine lactones (HSL), quorum sensing molecules specific of Pseudomonas Aeruginosa and other gram negative species. Nevertheless, these bacteria are not the major pathogens found in CRS. Here we report on the identification of bacterial metabolites acting as new agonists of T2R38 based on a single cell calcium imaging study. Two quorum sensing molecules (Agr D1 thiolactone from Staphylococcus Aureus and CSP-1 from Streptococcus Pneumoniae) and a list of 32 bacterial metabolites from pathogens frequently implicated in CRS were tested. First, we observed that HSL failed to activate T2R38 in our experimental system, but that the dimethylsulfoxide (DMSO), used as a solvent for these lactones may, by itself, account for the agonistic effect previously described. Secondly, we showed that both Agr D1 thiolactone and CSP-1 are inactive but that at least 7 bacterial metabolites (acetone, 2-butanone, 2-pentanone, 2-methylpropanal, dimethyl disulfide, methylmercaptan, γ-butyrolactone) are able to specifically trigger this receptor. T2R38 is thus much more broadly tuned for bacterial compounds than previously thought.

ATG16L1 phosphorylation is oppositely regulated by CSNK2/casein kinase 2 and PPP1/protein phosphatase 1 which determines the fate of cardiomyocytes during hypoxia/reoxygenation

Recent studies have shown that the phosphorylation and dephosphorylation of ULK1 and ATG13 are related to autophagy activity. Although ATG16L1 is absolutely required for autophagy induction by affecting the formation of autophagosomes, the post-translational modification of ATG16L1 remains elusive. Here, we explored the regulatory mechanism and role of ATG16L1 phosphorylation for autophagy induction in cardiomyocytes. We showed that ATG16L1 was a phosphoprotein, because phosphorylation of ATG16L1 was detected in rat cardiomyocytes during hypoxia/reoxygenation (H/R). We not only demonstrated that CSNK2 (casein kinase 2) phosphorylated ATG16L1, but also identified the highly conserved Ser139 as the critical phosphorylation residue for CSNK2. We further established that ATG16L1 associated with the ATG12-ATG5 complex in a Ser139 phosphorylation-dependent manner. In agreement with this finding, CSNK2 inhibitor disrupted the ATG12-ATG5-ATG16L1 complex. Importantly, phosphorylation of ATG16L1 on Ser139 was responsible for H/R-induced autophagy in cardiomyocytes, which protects cardiomyocytes from apoptosis. Conversely, we determined that wild-type PPP1 (protein phosphatase 1), but not the inactive mutant, associated with ATG16L1 and antagonized CSNK2-mediated phosphorylation of ATG16L1. Interestingly, one RVxF consensus site for PPP1 binding in the C-terminal tail of ATG16L1 was identified; mutation of this site disrupted its association with ATG16L1. Notably, CSNK2 also associated with PPP1, but ATG16L1 depletion impaired the interaction between CSNK2 and PPP1. Collectively, these data identify ATG16L1 as a bona fide physiological CSNK2 and PPP1 substrate, which reveals a novel molecular link from CSNK2 to activation of the autophagy-specific ATG12-ATG5-ATG16L1 complex and autophagy induction.

Cardiomyocyte-derived CXCL12 is not involved in cardiogenesis but plays a crucial role in myocardial infarction

The chemokine CXCL12/SDF-1 is crucial for heart development and affects cardiac repair processes due to its ability to attract leukocytes and stem cells to injured myocardium. However, there is a great controversy whether CXCL12 is beneficial or detrimental after myocardial infarction (MI). The divergence in the reported CXCL12 actions may be due to the cellular source and time of release of the chemokine after MI. This study was designed to evaluate the role of cardiomyocyte-derived CXCL12 for cardiogenesis and heart repair after MI. We generated two rodent models each targeting CXCL12 in only one cardiac cell type: cardiomyocyte-specific CXCL12-overexpressing transgenic (Tg) rats and CXCL12 conditional knockout (cKO) mice. Animals of both models did not show any signs of cardiac abnormalities under baseline conditions. After induction of MI, cKO mice displayed preserved cardiac function and remodeling. Moreover, fibrosis was less pronounced in the hearts of cKO mice after MI. Accordingly, CXCL12 Tg rats revealed impaired cardiac function post-MI accompanied by enhanced fibrosis. Furthermore, we observed decreased numbers of infiltrating Th1 cells in the hearts of cKO mice. Collectively, our findings demonstrate that cardiomyocyte-derived CXCL12 is not involved in cardiac development but has adverse effects on the heart after injury via promotion of inflammation and fibrosis.

KEY MESSAGES

• CXCL12 in cardiomyocytes is not involved in cardiac development. • CXCL12 deficiency in cardiomyocytes improves outcome of myocardial infarction. • CXCL12 overexpression in cardiomyocytes worsens outcome of myocardial infarction. • CXCL12 increases fibrosis and invasion of Th1 cells in the heart after infarction.

The development and characterization of SDF1α-elastin-like-peptide nanoparticles for wound healing

Chronic skin wounds are characterized by poor re-epithelialization, angiogenesis and granulation. Previous work has demonstrated that topical stromal cell-derived growth factor-1 (SDF1) promotes neovascularization, resulting in faster re-epithelialization of skin wounds in diabetic mice. However, the clinical usefulness of such bioactive peptides is limited because they are rapidly degraded in the wound environment due to high levels of proteases. Here, we describe the development of a recombinant fusion protein comprised of SDF1 and an elastin-like peptide that confers the ability to self-assemble into nanoparticles. The fusion protein and recombinant human SDF1 showed similar binding characteristics, as indicated by the measured equilibrium dissociation constant (Kd) for the binding of free SDF1 or the fusion protein to the CXCR4 receptor. The biological activity of SDF1-ELP, as measured by intracellular calcium release in HL60 cells was dose dependent, and also very similar to that of free SDF1. In contrast, the biological activity of SDF1-ELP in vivo was significantly superior to that of free SDF1. When applied to full thickness skin wounds in diabetic mice, wounds treated with SDF1-ELP nanoparticles were 95% closed by day 21, and fully closed by day 28, while wounds treated with free SDF1, ELP alone, or vehicle were only 80% closed by day 21, and took 42days to fully close. In addition, the SDF1-ELP nanoparticles significantly increased the epidermal and dermal layer of the healed wound, as compared to the other groups. These results indicate that SDF1-ELP fusion protein nanoparticles are promising agents for the treatment of chronic skin wounds.

Diversity and Inter-Connections in the CXCR4 Chemokine Receptor/Ligand Family: Molecular Perspectives

CXCR4 and its ligand CXCL12 mediate the homing of progenitor cells in the bone marrow and their recruitment to sites of injury, as well as affect processes such as cell arrest, survival, and angiogenesis. CXCL12 was long thought to be the sole CXCR4 ligand, but more recently the atypical chemokine macrophage migration inhibitory factor (MIF) was identified as an alternative, non-cognate ligand for CXCR4 and shown to mediate chemotaxis and arrest of CXCR4-expressing T-cells. This has complicated the understanding of CXCR4-mediated signaling and associated biological processes. Compared to CXCL12/CXCR4-induced signaling, only few details are known on MIF/CXCR4-mediated signaling and it remains unclear to which extent MIF and CXCL12 reciprocally influence CXCR4 binding and signaling. Furthermore, the atypical chemokine receptor 3 (ACKR3) (previously CXCR7) has added to the complexity of CXCR4 signaling due to its ability to bind CXCL12 and MIF, and to evoke CXCL12- and MIF-triggered signaling independently of CXCR4. Also, extracellular ubiquitin (eUb) and the viral protein gp120 (HIV) have been reported as CXCR4 ligands, whereas viral chemokine vMIP-II (Herpesvirus) and human β3-defensin (HBD-3) have been identified as CXCR4 antagonists. This review will provide insight into the diversity and inter-connections in the CXCR4 receptor/ligand family. We will discuss signaling pathways initiated by binding of CXCL12 vs. MIF to CXCR4, elaborate on how ACKR3 affects CXCR4 signaling, and summarize biological functions of CXCR4 signaling mediated by CXCL12 or MIF. Also, we will discuss eUb and gp120 as alternative ligands for CXCR4, and describe vMIP-II and HBD-3 as antagonists for CXCR4. Detailed insight into biological effects of CXCR4 signaling und underlying mechanisms, including diversity of CXCR4 ligands and inter-connections with other (chemokine) receptors, is clinically important, as the CXCR4 antagonist AMD3100 has been approved as stem cell mobilizer in specific disease settings.

Deorphanization and characterization of human olfactory receptors in heterologous cells

Olfaction plays an indispensable role in human and animals in self and environmental recognition, as well as intra- and interspecific communication. Following the discovery of a family of olfactory receptors (ORs) by Buck and Axel in 1991, it has been established that the sense of smell begins with the molecular recognition of a chemical odorant by one or more ORs expressed in the olfactory sensory neurons. Therefore, characterization of the molecular interactions between odorant molecules and ORs is a key step in the elucidation of the general properties of the olfactory system and in the development of applications, i.e., design of new odorants, search for blockers, etc. The process putted in place at ChemCom to improve the expression of ORs at the cytoplasmic membrane of the HEK293 cell and assays enabling large-scale deorphanization, and to characterize the interaction between chemical odorants and ORs is described. The family of human ORs includes ca. 400 putatively functional ORs which are GPCRs (G protein-coupled receptors); to date over 100 human ORs have been deorphanized.

Conversion of mouse fibroblasts into cardiomyocyte-like cells using small molecule treatments

The possibility of controlling cell fates by overexpressing specific transcription factors has led to numerous studies in stem cell research. Small molecules can be used, instead of transcription factors, to induce the de-differentiation of somatic cells or to induce pluripotent cells (iPSCs). Here we reported that combinations of small molecules could convert mouse fibroblasts into cardiomyocyte-like cell without requiring transcription factor expression. Treatment with specific combinations of small molecules that are enhancer for iPSC induction converted mouse fibroblasts into spontaneously contracting, cardiac troponin T-positive, cardiomyocyte-like cells. We specifically identified five small molecules that can induce mouse fibroblasts to form these cardiomyocyte-like cells. These cells are similar to primary cardiomyocytes in terms of marker gene expression, epigenetic status of cardiac-specific genes, and subcellular structure. Our findings indicate that lineage conversion can be induced not only by transcription factors, but also by small molecules.

Inhibiting the mobilization of Ly6C(high) monocytes after acute myocardial infarction enhances the efficiency of mesenchymal stromal cell transplantation and curbs myocardial remodeling

BACKGROUND

Ischemia related inflammation is the most critical factor for the survival of transplanted mesenchymal stem cells (MSCs), and strategies for controlling excessive inflammation after acute myocardial infarction (AMI) are essential and necessary for cell transplantation therapy. Our present study tested the effect of decreased Ly6C(high) monocytes on mouse MSCs transplantation after AMI.

METHODS

BALB/c AMI mice were treated systemically with a CCR2 antagonist (RS 504393, 2 mg/kg, subcutaneously) or normal saline (control group). Next, 10(5) EdU-labeled MSCs were administered by intramyocardial injection to the mice in each group. TUNEL kits were used to identify the apoptotic cardiomyocytes in the infarct. The slides of the infarct border zone were stained with wheat germ agglutinin to measure the vessel density, and anti-myosin heavy chain eFluor 660 was used to measure the cardiac myosin-positive area. A transwell chamber was used to examine the interactions between Ly6C(high) monocytes and MSCs. The inflammatory cytokines expressed by Ly6C(high) monocytes and the SDF-1 expressed by MSCs were detected using ELISA kits. MSC viability was further examined by MTT and mitochondrial membrane potential assays by flow cytometry using JC-1 kits.

RESULTS

We first observed the increased survival of transplanted MSCs (11.2 ± 3.4/mm(2) vs. 3.5 ± 1.6/mm(2), p < 0.001), and the decreased apoptosis of cardiomyocytes (11.20% ± 3.55% vs. 20.51% ± 8.17%, p < 0.001) in the infarcts at 3 days in the CCR2 antagonist group. An increased number of capillaries and small arterioles (139.6 ± 21.7/mm(2) vs. 95.4 ± 17.6/mm(2), p < 0.001) and an increased cardiac myosin-positive area (17.9% ± 6.6% vs. 11.8% ± 3.5%, p < 0.001) were also observed in the infarct zone at 21 days post MSC infusion in the CCR2 antagonist group. In addition, a significantly increased LvEF% (50.17 ± 10.06 vs. 45.44 ± 9.45, p < 0.001) was detected at the same time compared to the control mice. We further demonstrated that both the mitochondrial membrane potential of the MSCs (0.45 ± 0.11 vs. 3.4 ± 0.3, p < 0.001) and stromal cell-derived factor-1 (SDF-1) secreted by the MSCs significantly decreased (80.77 ± 39.02 pg/ml vs. 435.5 ± 77.41 pg/ml, p < 0.001) when co-cultured with Ly6C(high) monocytes. This is possibly mediated by the over-expressed cytokines secreted by the Ly6C(high) monocytes compared to the Ly6C(low) monocytes, including IL-1 (139.45 ± 30.44 vs. 80.05 ± 19.33, p < 0.001), IL-6 (187.82 ± 40.43 vs. 135.5 ± 22.09, p < 0.001), TNF-α (121.77 ± 31.65 vs. 75.3 ± 22.14, p < 0.001) and IFN-γ (142.46 ± 27.55 vs. 88.25 ± 19.91, p < 0.001).