Cardiac delivery of modified mRNA using lipid nanoparticles: Cellular targets and biodistribution after intramyocardial administration.

Despite research efforts being made towards preserving (or even regenerating) heart tissue after an ischemic event, there is a lack of resources in current clinical treatment modalities for patients with acute myocardial infarction that specifically address cardiac tissue impairment. Modified messenger RNA (modRNA) presents compelling properties that could allow new therapeutic strategies to tackle the underlying molecular pathways that ultimately lead to development of chronic heart failure. However, clinical application of modRNA for the heart is challenged by the lack of effective and safe delivery systems. Lipid nanoparticles (LNPs) represent a well characterized class of RNA delivery systems, which were recently approved for clinical usage in mRNA-based COVID-19 vaccines. In this study, we evaluated the potential of LNPs for cardiac delivery of modRNA. We tested how variations in C12-200 modRNA-LNP composition affect transfection levels and biodistribution after intramyocardial administration in both healthy and myocardial-infarcted mice, and determined the targeted cardiac cell types. Our data revealed that LNP-mediated modRNA delivery outperforms the current state of the art (modRNA in citrate buffer) upon intramyocardial administration in mice, with only minor differences among the formulations tested. Furthermore, we determined both in vitro and in vivo that the cardiac cells targeted by modRNA-LNPs include fibroblasts, endothelial cells and epicardial cells, suggesting that these cell types could represent targets for therapeutic interference with these LNP formulations. These outcomes may serve as a starting point for LNP development specifically for therapeutic mRNA cardiac delivery applications.

Restraining FOXO3-dependent transcriptional BMF activation underpins tumour growth and metastasis of E-cadherin-negative breast cancer.

Loss of cellular adhesion leads to the progression of breast cancer through acquisition of anchorage independence, also known as resistance to anoikis. Although inactivation of E-cadherin is essential for acquisition of anoikis resistance, it has remained unclear how metastatic breast cancer cells counterbalance the induction of apoptosis without E-cadherin-dependent cellular adhesion. We report here that E-cadherin inactivation in breast cancer cells induces PI3K/AKT-dependent FOXO3 inhibition and identify FOXO3 as a novel and direct transcriptional activator of the pro-apoptotic protein BMF. As a result, E-cadherin-negative breast fail to upregulate BMF upon transfer to anchorage independence, leading to anoikis resistance. Conversely, expression of BMF in E-cadherin-negative metastatic breast cancer cells is sufficient to inhibit tumour growth and dissemination in mice. In conclusion, we have identified repression of BMF as a major cue that underpins anoikis resistance and tumour dissemination in E-cadherin-deficient metastatic breast cancer.

Young at heart. An update on cardiac regeneration.

Cardiovascular disease remains one of the most important causes of mortality. Over the past decades important advances have been made in prevention and treatment of acute complications after myocardial infarction (MI). As a result, the number of patients that acutely die from MI has been reduced. Current treatments can not prevent the loss of cardiac contractility caused by cardiomyocyte death, and therefore patients that do survive MI are prone to develop progressive impaired cardiac function, which may lead to heart failure. Cell-based therapy has been proposed as a potential new therapy to prevent progression to end-stage heart failure by (re)generating contractile tissue in the damaged heart. During the last years many different cell sources have been studied extensively for their cardiomyogenic differentiation capacity in vitro and in vitro. These cells include several populations of cardiac-derived progenitor cells as well as mesenchymal stem cells derived from different sources. It has become clear that not only the origin, but also the "age" of a cell is an important determinant of its plasticity. Therefore, special attention is paid to the difference in developmental state of the cell sources and the consequences for their differentiation capacity and therapeutic applicability. Furthermore, we provide future perspectives for several aspects of cell-based therapy that could be optimized in order to enhance the regeneration of the heart.

Stem cells: the building blocks to repair the injured heart.

Myocardial infarction is the major cause of death in western countries due to impaired function of the heart, which is the result of cardiomyocyte death and fibrotic scar formation. The endogenous regenerative capacity of the heart is unable to replenish this significant loss of tissue and conventional medical management cannot correct the underlying defects in cardiac muscle cell number. Recently, tremendous effort is being put into the development of cell transplantation protocol for heart repair, which has been put forward as an alternative therapy to reduce cell damage, cardiomyocyte death and improve tissue contraction. Unfortunately the ideal stem cell population for heart repair has not been identified to date, but several characteristics are defined which the ideal population should have namely, reduce cell damage, reduce cardiomyocyte death, induce differentiation into cardiomyocytes and endothelial cells, and improve tissue contraction. It is unclear whether this will be possible in one optimal population. Therefore the research focus is shifting towards improving the characteristics of the stem cell populations that are identified to date. In this review, we will give an overview of the different stem/progenitor cell populations and their application in cardiac repair and discuss current knowledge on issues like differentiation capacity, paracrine secretion profile, genetic modification of progenitor cells and their influence on cardiac remodeling.

Progenitor cells isolated from the human heart: a potential cell source for regenerative therapy.

BACKGROUND: In recent years, resident cardiac progenitor cells have been identified in, and isolated from the rodent heart. These cells show the potential to form cardiomyocytes, smooth muscle cells, and endothelial cells in vitro and in vivo and could potentially be used as a source for cardiac repair. However, previously described cardiac progenitor cell populations show immature development and need co-culture with neonatal rat cardiomyocytes in order to differentiate in vitro. Here we describe the localisation, isolation, characterisation, and differentiation of cardiomyocyte progenitor cells (CMPCs) isolated from the human heart. METHODS: hCMPCs were identified in human hearts based on Sca-1 expression. These cells were isolated, and FACS, RT-PCR and immunocytochemistry were used to determine their baseline characteristics. Cardiomyogenic differentiation was induced by stimulation with 5-azacytidine. RESULTS: hCMPCs were localised within the atria, atrioventricular region, and epicardial layer of the foetal and adult human heart. In vitro, hCMPCs could be induced to differentiate into cardiomyocytes and formed spontaneously beating aggregates, without the need for co-culture with neonatal cardiomyocytes. CONCLUSION: The human heart harbours a pool of resident cardiomyocyte progenitor cells, which can be expanded and differentiated in vitro. These cells may provide a suitable source for cardiac regeneration cell therapy. (Neth Heart J 2008;16:163-9.).

A novel real-time PCR assay to determine relative replication capacity for HIV-1 protease variants and/or reverse transcriptase variants.

The emergence of drug-resistant viruses is a major issue in the treatment of HIV-1 infections. Quite often these drug-resistant viruses have a reduced replication capacity. A novel assay was developed to study the impact of mutations selected during therapy on viral replication capacity. Two HIV-1 HXB2 reference clones were constructed for this assay based on viral competition experiments, which are identical except for the presence of two silent nucleotide changes in p24 in one of the two clones. Within these two reference clones, three different contiguous deletions were constructed: (I) the C-terminus of Gag and protease, (II) the N-terminus of RT and (III) the C-terminus of Gag and protease together with the N-terminus of RT. Using these reference clones, recombinant viruses were created and viral competition experiments were performed. The proportion of each virus during the competition experiments was determined with a real-time PCR assay based on the two silent nucleotide changes in p24 in one of the two reference clones. With this novel assay it was possible to detect accurately differences in replication capacity due to mutations in the C-terminus of Gag and protease and/or the N-terminus of RT.

Direct control of the Forkhead transcription factor AFX by protein kinase B.

The phosphatidylinositol-3-OH-kinase (PI(3)K) effector protein kinase B regulates certain insulin-responsive genes, but the transcription factors regulated by protein kinase B have yet to be identified. Genetic analysis in Caenorhabditis elegans has shown that the Forkhead transcription factor daf-16 is regulated by a pathway consisting of insulin-receptor-like daf-2 and PI(3)K-like age-1. Here we show that protein kinase B phosphorylates AFX, a human orthologue of daf-16, both in vitro and in vivo. Inhibition of endogenous PI(3)K and protein kinase B activity prevents protein kinase B-dependent phosphorylation of AFX and reveals residual protein kinase B-independent phosphorylation that requires Ras signalling towards the Ral GTPase. In addition, phosphorylation of AFX by protein kinase B inhibits its transcriptional activity. Together, these results delineate a pathway for PI(3)K-dependent signalling to the nucleus.

Essential role for protein kinase B (PKB) in insulin-induced glycogen synthase kinase 3 inactivation. Characterization of dominant-negative mutant of PKB.

Activation of phosphatidylinositide 3'-OH kinase (PI 3-kinase) is implicated in mediating a variety of growth factor-induced responses, among which are the inactivation of glycogen synthase kinase-3 (GSK-3) and the activation of the serine/threonine protein kinase B (PKB). GSK-3 inactivation occurs through phosphorylation of Ser-9, and several kinases, such as protein kinase C, mitogen-activated protein kinase-activated protein kinase-1 (p90(Rsk)), p70(S6kinase), and also PKB have been shown to phosphorylate this site in vitro. In the light of the many candidates to mediate insulin-induced GSK-3 inactivation we have investigated the role of PKB by constructing a PKB mutant that exhibits dominant-negative function (inhibition of growth factor-induced activation of PKB at expression levels similar to wild-type PKB), as currently no such mutant has been reported. We observed that the PKB mutant (PKB-CAAX) acts as an efficient inhibitor of PKB activation and also of insulin-induced GSK-3 regulation. Furthermore, it is shown that PKB and GSK-3 co-immunoprecipitate, indicating a direct interaction between GSK-3 and PKB. An additional functional consequence of this interaction is implicated by the observation that the oncogenic form of PKB, gagPKB induces a cellular relocalization of GSK-3 from the cytosolic to the membrane fraction. Our results demonstrate that PKB activation is both necessary and sufficient for insulin-induced GSK-3 inactivation and establish a linear pathway from insulin receptor to GSK-3. Regulation of GSK-3 by PKB is likely through direct interaction, as both proteins co-immunoprecipitate. This interaction also resulted in a translocation of GSK-3 to the membrane in cells expressing transforming gagPKB.

RalGDS-like factor (Rlf) is a novel Ras and Rap 1A-associating protein.

The small GTPase Rap 1A is a close relative of Ras that, when overexpressed, is able to revert oncogenic transformation induced by active Ras. We screened a mouse embryonic cDNA library using the yeast two-hybrid system and isolated the cDNA of a novel Rap 1A-interacting protein. The open reading frame encodes for an 84 kDa protein with a Cdc25-homology domain which shares approximately 30% identity with Ral guanine nucleotide dissociation stimulator (RalGDS) and RalGDS-like (Rg1). The C-terminal region reveals a striking conservation of sequences with the Ras-binding domain of RalGDS. We designated this protein Rlf, for RalGDS-like factor. In the yeast system, Rlf interacts with Rap 1A, H-Ras and R-Ras, but not with Rac and Rho. In addition, we found that Rlf interacts with Rap 1Aval12 but not with Rap 1AAsn17. In vitro binding studies revealed that a C-terminally located 91 amino acid region of Rlf is sufficient for direct association with the GTP-bound form of Ras and Rap 1A. The observed dissociation constants are 0.6 microM and 0.4 microM, respectively. No significant association with Ras-GDP or Rap 1A-GDP could be detected. These binding characteristics indicate that Rlf is a putative effector for Ras and Rap 1A.

Rac-dependent and -independent pathways mediate growth factor-induced Ca2+ influx.

We report that expressing interfering mutants of the small Ras-related GTPase Rac, using either recombinant vaccinia virus or stable DNA transfection, eliminates epidermal growth factor-induced Ca2+ signaling, without affecting Ca2+ mobilization or influx from G protein-coupled receptors. Platelet-derived growth factor-dependent Ca2+ influx, however, is only partly sensitive to dominant negative Rac proteins. Thus, whereas epidermal growth factor-induced Ca2+ influx is completely mediated by Rac proteins, platelet-derived growth factor-induced Ca2+ influx involves Rac-dependent and -independent signaling pathways.

Insulin-induced tyrosine phosphorylation of a M(r) 70,000 protein revealed by association with the Src homology 2 (SH2) and SH3 domains of p120GAP and Grb2.

We have used two approaches to identify possible substrates of the insulin receptor (IR) tyrosine kinase. First, we used a potent tyrosine phosphatase inhibitor, phenylarsine oxide (PAO), which is reported to be specific for the insulin-induced signal transduction route, to augment tyrosine phosphorylation. Second, we used src homology 2 (SH2) domains fused to glutathione S-transferase as high affinity binding agents for tyrosine-phosphorylated proteins. Using the SH2 domain-containing region of p120 GTPase-activating protein and growth factor-bound protein 2, we observed a tyrosine-phosphorylated M(r) 70,000 protein in insulin- plus PAO-treated NIH3T3 cells overexpressing the IR. This M(r) 70,000 protein, which migrated as a doublet on SDS-polyacrylamide gels, efficiently bound to polyuridylic acid-Sepharose but is distinct from similar-size RNA-binding proteins such as p62 (sam68) and heterogeneous nuclear ribonucleoproteins I, K, L, and M. In addition, it differs from other M(r) 70,000 tyrosine-phosphorylated proteins, such as SH2-containing tyrosine phosphatase, raf1, and paxillin. Tyrosine phosphorylation of this protein was hardly observed after epidermal growth factor treatment. This suggests that the M(r) 70,000 protein is a novel and specific substrate for the IR kinase or an insulin-induced tyrosine kinase. The requirement for PAO to identify this tyrosine phosphorylation indicates a high turnover rate of the tyrosine phosphate.

Calcium induces tyrosine phosphorylation of a novel p120GAP-associated protein of 65 kDa.

Several tyrosine-phosphorylated proteins have been identified that associate with p120GAP, the GTPase activating protein of p21ras. In keratinocytes, calcium induced the tyrosine phosphorylation of a 65 kDa p120GAP-associated protein (p65Ca). This protein did not comigrate with two previously reported p120GAP-associated proteins, i.e. a 68 kDa protein from src-transformed cells (p68) and an insulin-induced protein of 60 kDa (p60(2C4)). P65Ca was neither recognized by poly(U)-sepharose, which efficiently precipitates p68, nor did it crossreact with antibodies against p68. In addition, a monoclonal antibody directed to p60(2C4) did not recognize p65Ca. From these results we conclude that p65Ca is different from p68 and p60(2C4) and thus, a novel p120GAP-associated protein. Since calcium has an important, tyrosine kinase dependent, role in the differentiation of keratinocytes, phosphorylation of p65Ca may be important for this differentiation process. However, surprisingly, calcium induced the phosphorylation of a similar-sized p120GAP-associated 65 kDa protein in fibroblast cell lines.

Rac mediates growth factor-induced arachidonic acid release.

Growth factor-induced stress fiber formation involves signal transduction through Rac and Rho proteins and production of leukotrienes from arachidonic acid metabolism. In exploring the relationship between these pathways, we found that Rac is essential for EGF-induced arachidonic acid production and subsequent generation of leukotrienes and that Rac V12, a constitutively activated mutant of Rac, generates leukotrienes in a growth factor-independent manner. Leukotrienes generated by EGF or Rac V12 are necessary and sufficient for stress fiber formation. Furthermore, leukotriene-dependent stress fiber formation requires Rho proteins. We have therefore identified elements of a pathway from growth factor receptors that includes Rac, arachidonic acid production, arachidonic acid metabolism to leukotrienes, and leukotriene-dependent Rho activation. This appears to be the major pathway by which Rac influences Rho-dependent cytoskeleton rearrangements.

Shc associates with an unphosphorylated form of the p21ras guanine nucleotide exchange factor mSOS.

Association of the p21ras guanine nucleotide exchange factor mSOS with tyrosine-phosphorylated Shc has been implicated in the activation of p21ras. In addition, after growth factor stimulation mSOS becomes phosphorylated as indicated by the appearance of a form of mSOS with reduced electrophoretic mobility. This phosphorylation is delayed with respect to Shc-Grb2-mSOS complex formation and activation of p21ras. To investigate the role of mSOS phosphorylation in further detail we have investigated the effect of phosphorylation on mSOS complex formation and p21ras activation. We found that Shc is associated with the unphosphorylated, faster migrating form of mSOS. Furthermore, although there is a correlation between the amount of complexes formed and the activation of p21ras, there is no such a correlation between mSOS phosphorylation and p21ras activation. In addition, inhibition of mSOS phosphorylation did not affect complex formation of mSOS with tyrosine phosphorylated Shc. Also, induction of mSOS phosphorylation prior to complex formation did not affect EGF-induced association of mSOS with Shc significantly, and Shc still associated predominantly with the faster migrating form of mSOS. From these results we conclude that the unphosphorylated form of mSOS is associated with Shc and that perhaps a phosphorylation-dephosphorylation step is part of the mSOS activation-inactivation cycle.

B cell antigen receptor stimulation induces formation of a Shc-Grb2 complex containing multiple tyrosine-phosphorylated proteins.

Activation of growth factor receptor tyrosine kinases, such as the epidermal growth factor and insulin receptors, induces tyrosine phosphorylation of Shc proteins and their association with the SH2 domain-containing adaptor protein Grb2. The Shc-Grb2 complex has been implicated in coupling these receptors to p21ras. The B cell antigen receptor plays a key role in directing B cell proliferation and differentiation. Although the B cell receptor lacks intrinsic tyrosine kinase activity, its mode of action parallels that of receptor tyrosine kinases in many aspects. B cell receptor stimulation activates src-related tyrosine kinases and the tyrosine kinase syk, which leads to phosphorylation of various cytoplasmic proteins and initiates multiple signaling events, including p21ras activation. Therefore, we have investigated whether Shc proteins are targets for the activated B cell receptor. It was found that the 52- and 46-kDa forms of Shc are expressed in mature human B cells and become rapidly phosphorylated on tyrosine upon B cell receptor stimulation. Also, Shc is induced to associate with the Grb2 molecule and an undefined 130-kDa protein. In a specific response to B cell activation, the Shc-Grb2 complex associates with several tyrosine-phosphorylated proteins, including two prominent phosphoproteins with molecular masses of 130 and 110 kDa. These observations strongly suggest that the Shc and Grb2 adaptor proteins are involved in coupling the B cell antigen receptor to one or multiple signal transduction pathways.

Involvement of Shc in insulin- and epidermal growth factor-induced activation of p21ras.

Shc proteins are phosphorylated on tyrosine residues and associate with growth factor receptor-bound protein 2 (Grb2) upon treatment of cells with epidermal growth factor (EGF) or insulin. We have studied the role of Shc in insulin- and EGF-induced activation of p21ras in NIH 3T3 cells overexpressing human insulin receptors (A14 cells). A14 cells are equally responsive to insulin and EGF with respect to activation of p21ras. Analysis of Shc immunoprecipitates revealed that (i) both insulin and EGF treatment resulted in Shc tyrosine phosphorylation and (ii) Shc antibodies coimmunoprecipitated both Grb2 and mSOS after insulin and EGF treatment. The induction of tyrosine phosphorylation of Shc and the presence of Grb2 and mSOS in Shc immunoprecipitates followed similar time courses, with somewhat higher levels after EGF treatment. In mSOS immunoprecipitates, Shc could be detected as well. Furthermore, Shc immune complexes contained guanine nucleotide exchange activity toward p21ras in vitro. From these results, we conclude that after insulin and EGF treatment, Shc associates with both Grb2 and mSOS and therefore may mediate, at least in part, insulin- and EGF-induced activation of p21ras. In addition, we investigated whether the Grb2-mSOS complex associates with the insulin receptor or with insulin receptor substrate 1 (IRS1). Although we observed association of Grb2 with IRS1, we did not detect complex formation between mSOS and IRS1 in experiments in which the association of mSOS with Shc was readily detectable. Furthermore, whereas EGF treatment resulted in the association of mSOS with the EGF receptor, insulin treatment did not result in the association of mSOS with the insulin receptor. These results indicate that the association of Grb2-nSOS with Shc may be an important event in insulin-induced, mSOS-mediated activation of p21ras.

Epidermal growth factor induces phosphorylation of extracellular signal-regulated kinase 2 via multiple pathways.

Expression of p21rasAsn-17, a dominant negative mutant of p21ras that blocks p21ras activation by growth factors, inhibits activation of extracellular signal-regulated kinase 2 (ERK2) by insulin and platelet-derived growth factor in rat-1 cells [A. M. M. de Vries-Smits, B. M. T. Burgering, S. J. Leevers, C. J. Marshall, and J. L. Bos, Nature (London) 357:602-604, 1992]. Here we report that expression of p21rasAsn-17 does not abolish epidermal growth factor (EGF)-induced phosphorylation of ERK2 in fibroblasts. Since EGF activates p21ras in these cells, this indicates that EGF induces a p21ras-independent pathway for the phosphorylation of ERK2 as well. We investigated whether activation of protein kinase C (PKC) or increase in intracellular calcium could be involved in p21ras-independent signaling. In rat-1 cells, inhibition of either PKC, by prolonged 12-O-tetradecanoylphorbol-13-acetate (TPA) pretreatment, or calcium influx, by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) pretreatment, did not abolish EGF-induced ERK2 phosphorylation. However, a combined inhibition of both p21ras and calcium influx, but not PKC, resulted in a complete inhibition of EGF-induced ERK2 phosphorylation. In contrast, in Swiss 3T3 cells, inhibition of both p21ras activation and TPA-sensitive PKC, but not calcium influx, inhibited EGF-induced ERK2 phosphorylation. These results demonstrate that in fibroblasts, EGF induces alternative pathways of ERK2 phosphorylation in a cell-type-specific manner.