Stem cell factor/c-kit signaling mediated cardiac stem cell migration via activation of p38 MAPK

Causal effects of inflammatory cytokines on cardiovascular diseases: Insights from genetic evidence

Background

The causal relationship between inflammatory cytokines and cardiovascular diseases (CVDs) has not been fully elucidated. Exploring this relationship between circulating inflammatory cytokines and CVDs is crucial for early clinical diagnosis and effective treatment.

Methods and Results

This study investigated the causal relationships between 41 inflammatory cytokines and six CVDs: heart failure (HF), myocardial infarction (MI), unstable angina pectoris (UAP), stable angina pectoris (SAP), valvular heart disease (VHD), and aortic aneurysm (AA), using the Mendelian Randomization (MR) method. The primary analysis employed the inverse-variance weighted (IVW) method within MR. Heterogeneity and pleiotropy were assessed through MR-Egger regression and the Q statistic. Strong evidence supported the effect of macrophage inflammatory protein-1β (MIP-1β) on MI (OR = 1.062, P < 0.001, FDR <0.001). Suggestive evidence showed that the Beta nerve growth factor increased the risk of MI (OR = 1.145, P = 0.025), but the stem cell factor (SCF) demonstrated a potential protective effect against MI (OR = 0.910, P = 0.04). SCF and hepatocyte growth factor (HGF) exhibited potential protective effects against SAP. No inflammatory cytokine was associated with UAP. Monocyte chemotactic protein-1 was linked to an increased risk of VHD (OR = 1.056, P = 0.049). Higher levels of interleukin-13 (IL-13), interferon gamma-induced protein 10 (IP-10), and growth-regulated oncogene-alpha were associated with increased susceptibility to HF. Elevated basic fibroblast growth factor (bFGF) levels exhibited protective effects against AA (OR = 0.751, P = 0.038). Reverse MR analyses revealed that AA significantly decreased circulating TNF-related apoptosis-inducing ligand (TRAIL) levels (OR = 0.907, P < 0.001, FDR = 0.01). MI significantly increased circulating IL-12-p70 levels (OR = 1.146, P < 0.001, FDR = 0.014). Suggestive evidence indicated the Causal effects of six CVDs on 17 circulating inflammatory cytokines.

Conclusions

This study clarified the causal relationships between specific inflammatory cytokines and six CVDs, providing novel insights and evidence into the genetic involvement of inflammatory cytokines in CVDs. These inflammatory cytokines may be potential biomarkers for early disease diagnosis and treatment evaluation.

Novel Germline KIT Variants in Families With Severe Piebaldism: Case Series and Literature Review

INTRODUCTION

Piebaldism is a rare autosomal dominant disorder characterized by congenital white forelock and depigmented patches, which is most commonly caused by deleterious variants in the KIT gene.

METHODS

Four KIT variants were identified in a piebaldism case series by whole-exome sequencing. Functional experiments, including in vitro minigene reporter assay and enzyme-linked immunosorbent assay, were carried out to elucidate the pathogenicity of the variants. The genotype-phenotype correlation was summarized through extensive literature reviewing.

RESULTS

All the four cases had severe piebaldism presented with typical white forelock and diffuse depigmentation on the ventral trunk and limbs. Four germline variants at the tyrosine kinase (TK) domains of the KIT gene were identified: two novel variants c.1990+1G>A (p.Pro627_Gly664delinsArg) and c.2716T>C (p.Cys906Arg), and two known variants c.1879+1G>A (p.Gly592_Pro627delinsAla) and c.1747G>A (p.Glu583Lys). Both splicing variants caused exon skipping and inframe deletions in the TK1 domain. The missense variants resided at the TK1 and TK2 domains respectively impairing PI3K/AKT and MAPK/ERK signaling pathways, the downstream of KIT. All severe cases were associated with variants in the TK domains, eliciting a major dominant-negative mechanism of the disease.

CONCLUSION

Our data expand the mutation spectrum of KIT, emphasized by a dominant-negative effect of variants in the critical TK domains in severe cases. We also share the experience of prenatal diagnosis and informed reproductive choices for the affected families.

Healing the Broken Hearts: A Glimpse on Next Generation Therapeutics

Cardiovascular diseases are the leading cause of death worldwide, accounting for 32% of deaths globally and thus representing almost 18 million people according to WHO. Myocardial infarction, the most prevalent adult cardiovascular pathology, affects over half a million people in the USA according to the last records of the AHA. However, not only adult cardiovascular diseases are the most frequent diseases in adulthood, but congenital heart diseases also affect 0.8–1.2% of all births, accounting for mild developmental defects such as atrial septal defects to life-threatening pathologies such as tetralogy of Fallot or permanent common trunk that, if not surgically corrected in early postnatal days, they are incompatible with life. Therefore, both congenital and adult cardiovascular diseases represent an enormous social and economic burden that invariably demands continuous efforts to understand the causes of such cardiovascular defects and develop innovative strategies to correct and/or palliate them. In the next paragraphs, we aim to briefly account for our current understanding of the cellular bases of both congenital and adult cardiovascular diseases, providing a perspective of the plausible lines of action that might eventually result in increasing our understanding of cardiovascular diseases. This analysis will come out with the building blocks for designing novel and innovative therapeutic approaches to healing the broken hearts.

Dihydromyricetin ameliorates osteogenic differentiation of human aortic valve interstitial cells by targeting c-KIT/interleukin-6 signaling pathway

Aims: Calcific aortic valve disease (CAVD) is a chronic cardiovascular disease with high morbidity that lacks effective pharmacotherapeutics. As a natural flavonoid extracted from Ampelopsis grossedentata, dihydromyricetin (DHM) has been shown to be effective in protecting against atherosclerosis; yet, the therapeutic role of DHM in CAVD remains poorly understood. Herein, we aimed to clarify the therapeutic implications of DHM in CAVD and the underlying molecular mechanisms in human valvular interstitial cells (hVICs).

Methods and Results: The protein levels of two known osteogenesis-specific genes (alkaline phosphatase, ALP; runt-related transcription factor 2, Runx2) and calcified nodule formation in hVICs were detected by Western blot and Alizarin Red staining, respectively. The results showed that DHM markedly ameliorated osteogenic induction medium (OM)–induced osteogenic differentiation of hVICs, as evidenced by downregulation of ALP and Runx2 expression and decreased calcium deposition. The SwissTargetPrediction database was used to identify the potential AVC-associated direct protein target of DHM. Protein–protein interaction (PPI) analysis revealed that c-KIT, a tyrosine-protein kinase, can act as a credible protein target of DHM, as evidenced by molecular docking. Mechanistically, DHM-mediated inhibition of c-KIT phosphorylation drove interleukin-6 (IL-6) downregulation in CAVD, thereby ameliorating OM-induced osteogenic differentiation of hVICs and aortic valve calcification progression.

Conclusion: DHM ameliorates osteogenic differentiation of hVICs by blocking the phosphorylation of c-KIT, thus reducing IL-6 expression in CAVD. DHM could be a viable therapeutic supplement to impede CAVD.

Cardiac stem cells: Current knowledge and future prospects

Regenerative medicine is the field concerned with the repair and restoration of the integrity of damaged human tissues as well as whole organs. Since the inception of the field several decades ago, regenerative medicine therapies, namely stem cells, have received significant attention in preclinical studies and clinical trials. Apart from their known potential for differentiation into the various body cells, stem cells enhance the organ's intrinsic regenerative capacity by altering its environment, whether by exogenous injection or introducing their products that modulate endogenous stem cell function and fate for the sake of regeneration. Recently, research in cardiology has highlighted the evidence for the existence of cardiac stem and progenitor cells (CSCs/CPCs). The global burden of cardiovascular diseases’ morbidity and mortality has demanded an in-depth understanding of the biology of CSCs/CPCs aiming at improving the outcome for an innovative therapeutic strategy. This review will discuss the nature of each of the CSCs/CPCs, their environment, their interplay with other cells, and their metabolism. In addition, important issues are tackled concerning the potency of CSCs/CPCs in relation to their secretome for mediating the ability to influence other cells. Moreover, the review will throw the light on the clinical trials and the preclinical studies using CSCs/CPCs and combined therapy for cardiac regeneration. Finally, the novel role of nanotechnology in cardiac regeneration will be explored.

Cardiac stem cells: Current knowledge and future prospects

Regenerative medicine is the field concerned with the repair and restoration of the integrity of damaged human tissues as well as whole organs. Since the inception of the field several decades ago, regenerative medicine therapies, namely stem cells, have received significant attention in preclinical studies and clinical trials. Apart from their known potential for differentiation into the various body cells, stem cells enhance the organ's intrinsic regenerative capacity by altering its environment, whether by exogenous injection or introducing their products that modulate endogenous stem cell function and fate for the sake of regeneration. Recently, research in cardiology has highlighted the evidence for the existence of cardiac stem and progenitor cells (CSCs/CPCs). The global burden of cardiovascular diseases' morbidity and mortality has demanded an in-depth understanding of the biology of CSCs/CPCs aiming at improving the outcome for an innovative therapeutic strategy. This review will discuss the nature of each of the CSCs/CPCs, their environment, their interplay with other cells, and their metabolism. In addition, important issues are tackled concerning the potency of CSCs/CPCs in relation to their secretome for mediating the ability to influence other cells. Moreover, the review will throw the light on the clinical trials and the preclinical studies using CSCs/CPCs and combined therapy for cardiac regeneration. Finally, the novel role of nanotechnology in cardiac regeneration will be explored.

Behind the Scene: Exploiting MC1R in Skin Cancer Risk and Prevention

Melanoma and non-melanoma skin cancers (NMSCs) are the most frequent cancers of the skin in white populations. An increased risk in the development of skin cancers has been associated with the combination of several environmental factors (i.e., ultraviolet exposure) and genetic background, including melanocortin-1 receptor (MC1R) status. In the last few years, advances in the diagnosis of skin cancers provided a great impact on clinical practice. Despite these advances, NMSCs are still the most common malignancy in humans and melanoma still shows a rising incidence and a poor prognosis when diagnosed at an advanced stage. Efforts are required to underlie the genetic and clinical heterogeneity of melanoma and NMSCs, leading to an optimization of the management of affected patients. The clinical implications of the impact of germline MC1R variants in melanoma and NMSCs' risk, together with the additional risk conferred by somatic mutations in other peculiar genes, as well as the role of MC1R screening in skin cancers' prevention will be addressed in the current review.

Cell Sheet Comprised of Mesenchymal Stromal Cells Overexpressing Stem Cell Factor Promotes Epicardium Activation and Heart Function Improvement in a Rat Model of Myocardium Infarction

Cell therapy of the post-infarcted myocardium is still far from clinical use. Poor survival of transplanted cells, insufficient regeneration, and replacement of the damaged tissue limit the potential of currently available cell-based techniques. In this study, we generated a multilayered construct from adipose-derived mesenchymal stromal cells (MSCs) modified to secrete stem cell factor, SCF. In a rat model of myocardium infarction, we show that transplantation of SCF producing cell sheet induced activation of the epicardium and promoted the accumulation of c-kit positive cells in ischemic muscle. Morphometry showed the reduction of infarct size (16%) and a left ventricle expansion index (0.12) in the treatment group compared to controls (24-28%; 0.17-0.32). The ratio of viable myocardium was more than 1.5-fold higher, reaching 49% compared to the control (28%) or unmodified cell sheet group (30%). Finally, by day 30 after myocardium infarction, SCF-producing cell sheet transplantation increased left ventricle ejection fraction from 37% in the control sham-operated group to 53%. Our results suggest that, combining the genetic modification of MSCs and their assembly into a multilayered construct, we can provide prolonged pleiotropic effects to the damaged heart, induce endogenous regenerative processes, and improve cardiac function.

KIT and Melanoma: Biological Insights and Clinical Implications

Melanoma, originating from epidermal melanocytes, is a heterogeneous disease that has the highest mortality rate among all types of skin cancers. Numerous studies have revealed the cause of this cancer as related to various somatic driver mutations, including alterations in KIT-a proto-oncogene encoding for a transmembrane receptor tyrosine kinase. Although accounting for only 3% of all melanomas, mutations in c-KIT are mostly derived from acral, mucosal, and chronically sun-damaged melanomas. As an important factor for cell differentiation, proliferation, and survival, inhibition of c-KIT has been exploited for clinical trials in advanced melanoma. Here, apart from the molecular background of c-KIT and its cellular functions, we will review the wide distribution of alterations in KIT with a catalogue of more than 40 mutations reported in various articles and case studies. Additionally, we will summarize the association of KIT mutations with clinicopathologic features (age, sex, melanoma subtypes, anatomic location, etc.), and the differences of mutation rate among subgroups. Finally, several therapeutic trials of c-KIT inhibitors, including imatinib, dasatinib, nilotinib, and sunitinib, will be analyzed for their success rates and limitations in advanced melanoma treatment. These not only emphasize c-KIT as an attractive target for personalized melanoma therapy but also propose the requirement for additional investigational studies to develop novel therapeutic trials co-targeting c-KIT and other cytokines such as members of signaling pathways and immune systems.

An overview of the myocardial regeneration potential of cardiac c-Kit+ progenitor cells via PI3K and MAPK signaling pathways

In recent years, several studies have investigated cell transplantation as an innovative strategy to restore cardiac function following heart failure. Previous studies have also shown cardiac progenitor cells as suitable candidates for cardiac cell therapy compared with other stem cells. Cellular kit (c-kit) plays an important role in the survival and migration of cardiac progenitor cells. Like other types of cells, in the heart, cellular responses to various stimuli are mediated via coordinated pathways. Activation of c-kit⁺ cells leads to subsequent activation of several downstream mediators such as PI3K and the MAPK pathways. This review aims to outline current research findings on the role of PI3K/AKT and the MAPK pathways in myocardial regeneration potential of c-kit⁺.

Cardiac Progenitor Cells from Stem Cells: Learning from Genetics and Biomaterials

Cardiac Progenitor Cells (CPCs) show great potential as a cell resource for restoring cardiac function in patients affected by heart disease or heart failure. CPCs are proliferative and committed to cardiac fate, capable of generating cells of all the cardiac lineages. These cells offer a significant shift in paradigm over the use of human induced pluripotent stem cell (iPSC)-derived cardiomyocytes owing to the latter's inability to recapitulate mature features of a native myocardium, limiting their translational applications. The iPSCs and direct reprogramming of somatic cells have been attempted to produce CPCs and, in this process, a variety of chemical and/or genetic factors have been evaluated for their ability to generate, expand, and maintain CPCs in vitro. However, the precise stoichiometry and spatiotemporal activity of these factors and the genetic interplay during embryonic CPC development remain challenging to reproduce in culture, in terms of efficiency, numbers, and translational potential. Recent advances in biomaterials to mimic the native cardiac microenvironment have shown promise to influence CPC regenerative functions, while being capable of integrating with host tissue. This review highlights recent developments and limitations in the generation and use of CPCs from stem cells, and the trends that influence the direction of research to promote better application of CPCs.

Stem Cell Homing: a Potential Therapeutic Strategy Unproven for Treatment of Myocardial Injury

Despite advances in the prevention and therapeutic modalities of ischemic heart disease, morbidity and mortality post-infarction heart failure remain big challenges in modern society. Stem cell therapy is emerging as a promising therapeutic strategy. Stem cell homing, the ability of stem cells to find their destination, is receiving more attention. Identification of specific cues and understanding the signaling pathways that direct stem cells to targeted destination will improve stem cell homing efficiency. This review discusses the cellular and molecular mechanism of stem cell homing at length in the light of literature and analyzes the problem and considerations of this approach as a treatment strategy for the treatment of ischemic heart disease clinically.

Hypoxia-stressed cardiomyocytes promote early cardiac differentiation of cardiac stem cells through HIF-1α/Jagged1/Notch1 signaling

Hypoxia is beneficial for the differentiation of stem cells transplanted for myocardial injury, but mechanisms underlying this benefit remain unsolved. Here, we report the impact of hypoxia-induced Jagged1 expression in cardiomyocytes (CMs) for driving the differentiation of cardiac stem cells (CSCs). Forced hypoxia-inducible factor 1α (HIF-1α) expression and physical hypoxia (5% O₂) treatment could induce Jagged1 expression in neonatal rat CMs. Pharmacological inhibition of HIF-1α by YC-1 attenuated hypoxia-promoted Jagged1 expression in CMs. An ERK inhibitor (PD98059), but not inhibitors of JNK (SP600125), Notch (DAPT), NF-κB (PTDC), JAK (AG490), or STAT3 (Stattic) suppressed hypoxia-induced Jagged1 protein expression in CMs. c-Kit⁺ CSCs isolated from neonatal rat hearts using a magnetic-activated cell sorting method expressed GATA4, SM22α or vWF, but not Nkx2.5 and cTnI. Moreover, 87.3% of freshly isolated CSCs displayed Notch1 receptor expression. Direct co-culture of CMs with BrdU-labeled CSCs enhanced CSCs differentiation, as evidenced by an increased number of BrdU⁺/Nkx2.5⁺ cells, while intermittent hypoxia for 21 days promoted co-culture-triggered differentiation of CSCs into CM-like cells. Notably, YC-1 and DAPT attenuated hypoxia-induced differentiation. Our results suggest that hypoxia induces Jagged1 expression in CMs primarily through ERK signaling, and facilitates early cardiac lineage differentiation of CSCs in CM/CSC co-cultures via HIF-1α/Jagged1/Notch signaling.

HOXD10 silencing suppresses human fibroblast-like synoviocyte migration in rheumatoid arthritis via downregulation of the p38/JNK pathway

Homeobox D10 (HOXD10) belongs to the human homeobox (HOX) gene family, and the homologous protein encoded by HOX primarily controls cell differentiation and morphogenesis during embryonic development. The current study aimed to explore the roles and mechanisms of HOXD10 in the migration of human fibroblast-like synoviocytes in rheumatoid arthritis (RAFLS). Cell counting kit-8, cell migration and wound healing assays were performed to examine the cell viability and migration, respectively. Western blot and reverse transcription-quantitative polymerase chain reaction assays were used to evaluate the association between mRNA and protein expression levels. The results revealed HOXD10 expression was upregulated in tissues from patients with RA. HOXD10 silencing inhibited the viability of RAFLS. In addition, HOXD10 silencing suppressed the migration of RAFLS through modulating the expression of cadherin-11, N-cadherin, E-cadherin, vimentin, zonula occludens-1, integrinβ1 and paxillin. In conclusion, HOXD10 silencing downregulates the p38/c-Jun N-terminal kinase signaling pathway, which in turn may suppress the migration of RAFLS.

Leptin induces osteocalcin expression in ATDC5 cells through activation of the MAPK-ERK1/2 signaling pathway

Both leptin and osteocalcin have been found to affect growth-plate cartilage development through regulation of the physiologic processes of endochondral bone formation. Leptin mediates bone development and osteocalcin secreted in the late stage of osteoblast differentiation. The relationship between leptin and osteocalcin expression in the chondrogenic cells line is still not clear. Thus, the aim of this study was to explore the effect of leptin on the expression of osteocalcin in chondrocytes. We used clonal mouse chondrogenic ATDC5 cells to investigate the relationship between leptin and osteocalcin. We found that both leptin and osteocalcin expression were dynamically expressed during ATDC5 cell differentiation from 4 to 21 days. We also found that leptin significantly upregulated osteocalcin mRNA and protein levels 24 h after leptin stimulation. However, different concentrations and exposure times of osteocalcin did not affect the levels of leptin protein. Furthermore, we confirmed that leptin augmented the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in a time-dependent manner but not p38 or AKT. Inhibition of pERK1/2 expression by a specific ERK1/2 inhibitor U0126 and a special small interfering RNA attenuated levels of leptin-induced osteocalcin expression, indicating that ERK1/2 mediates, in part, the effects of leptin on osteocalcin. Taken together, our results suggest that leptin regulates the expression of osteocalcin in growth plate chondrocytes via the ERK1/2 signaling pathway, while there is no effect on the phosphorylation of either p38 or AKT.

CD117/c-kit in Cancer Stem Cell-Mediated Progression and Therapeutic Resistance

Metastasis is the primary cause of cancer patient morbidity and mortality, but due to persisting gaps in our knowledge, it remains untreatable. Metastases often occur as patient tumors progress or recur after initial therapy. Tumor recurrence at the primary site may be driven by a cancer stem-like cell or tumor progenitor cell, while recurrence at a secondary site is driven by metastatic cancer stem cells or metastasis-initiating cells. Ongoing efforts are aimed at identifying and characterizing these stem-like cells driving recurrence and metastasis. One potential marker for the cancer stem-like cell subpopulation is CD117/c-kit, a tyrosine kinase receptor associated with cancer progression and normal stem cell maintenance. Further, activation of CD117 by its ligand stem cell factor (SCF; kit ligand) in the progenitor cell niche stimulates several signaling pathways driving proliferation, survival, and migration. This review examines evidence that the SCF/CD117 signaling axis may contribute to the control of cancer progression through the regulation of stemness and resistance to tyrosine kinase inhibitors.

Leptin regulates disc cartilage endplate degeneration and ossification through activation of the MAPK-ERK signalling pathway in vivo and in vitro

Recent findings demonstrate that leptin plays a significant role in chondrocyte and osteoblast differentiation. However, the mechanisms by which leptin acts on cartilage endplate (CEP) cells to give rise to calcification are still unclear. The aim of this study was to evaluate the effects of leptin that induced mineralization of CEP cells in vitro and in vivo. We constructed a rat model of lumbar disc degeneration and determined that leptin was highly expressed in the presence of CEP calcification. Rat CEP cells treated with or without leptin were used for in vitro analysis using RT‐PCR and Western blotting to examine the expression of osteocalcin (OCN) and runt‐related transcription factor 2 (Runx2). Both OCN and Runx2 expression levels were significantly increased in a dose‐ and time‐dependent manner. Leptin activated ERK1/2 and STAT3 phosphorylation in a time‐dependent manner. Inhibition of phosphorylated ERK1/2 using targeted siRNA suppressed leptin‐induced OCN and Runx2 expression and blocked the formation of mineralized nodules in CEP cells. We further demonstrated that exogenous leptin induced matrix mineralization of CEP cells in vivo. We suggest that leptin promotes the osteoblastic differentiation of CEP cells via the MAPK/ERK signal transduction pathway and may be used to investigate the mechanisms of disc degeneration.

β-arrestin2 Affects Cardiac Progenitor Cell Survival through Cell Mobility and Tube Formation in Severe Hypoxia

Background and Objectives

β-arrestin2 (β-arr2) basically regulates multiple signaling pathways in mammalian cells by desensitization and internalization of G-protein coupled receptors (GPCRs). We investigated impacts of β-arr2 on survival, mobility, and tube formation of cardiac progenitor cells (CPCs) obtained from wild-type (WT) mouse (CPC-WT), and β-arr2 knock-out (KO) mouse (CPC-KO) cultured in presence or absence of serum and oxygen as non-canonical roles in GPCR system.

Methods

CPCs were cultured in Dulbecco's Modified Eagle Medium/Nutrient Mixture F-12 -based media containing fetal bovine serum and growth factors. Survival of 2 types of CPCs in hypoxia and/or serum deprivation was measured by fluorescence-activated cell sorting. Wound healing ability, and tube formation ability on Matrigel of 2 kinds of CPCs were compared in normoxic and hypoxic cultures. Protein expression related to survival and mobility were measured with the Western blot for each culture conditions.

Results

CPC-KO showed significantly worse mobility in the wound healing assay and in tube formation on Matrigel especially in hypoxic culture than did the CPC-WT. Also, CPC-KO showed significantly higher apoptosis fraction in both normoxic and hypoxic cultures than did the CPC-WT. Expression of proteins associated with cell survival and mobility, e.g., protein kinase B (Akt), β-catenin, and glycogen synthase kinase-3β (GSK-3β) was significantly worse in CPC-KO.

Conclusions

The CPC-KO had significantly worse cell mobility, tube formation ability, and survival than the CPC-WT, especially in the hypoxic cultures. Apparently, β-arr2 is important on CPC survival by means of mobility and tube formation in myocardial ischemia.

Concise Review: Challenges in Regenerating the Diabetic Heart: A Comprehensive Review

Stem cell therapy is one of the promising regenerative strategies developed to improve cardiac function in patients with ischemic heart diseases (IHD). However, this approach is limited in IHD patients with diabetes due to a progressive decline in the regenerative capacity of stem cells. This decline is mainly attributed to the metabolic memory incurred by diabetes on stem cell niche and their systemic cues. Understanding the molecular pathways involved in the diabetes-induced deterioration of stem cell function will be critical for developing new cardiac regeneration therapies. In this review, we first discuss the most common molecular alterations occurring in the diabetic stem cells/progenitor cells. Next, we highlight the key signaling pathways that can be dysregulated in a diabetic environment and impair the mobilization of stem/progenitor cells, which is essential for the transplanted/endogenous stem cells to reach the site of injury. We further discuss the possible methods of preconditioning the diabetic cardiac progenitor cell (CPC) with an aim to enrich the availability of efficient stem cells to regenerate the diseased diabetic heart. Finally, we propose new modalities for enriching the diabetic CPC through genetic or tissue engineering that would aid in developing autologous therapeutic strategies, improving the proliferative, angiogenic, and cardiogenic properties of diabetic stem/progenitor cells. Stem Cells 2017;35:2009-2026.

The stem cell factor (SCF)/c-KIT signalling in testis and prostate cancer

The stem cell factor (SCF) is a cytokine that specifically binds the tyrosine kinase receptor c-KIT. The SCF/c-KIT interaction leads to receptor dimerization, activation of kinase activity and initiation of several signal transduction pathways that control cell proliferation, apoptosis, differentiation and migration in several tissues. The activity of SCF/c-KIT system is linked with the phosphatidylinositol 3-kinase (PI3-K), the Src, the Janus kinase/signal transducers and activators of transcription (JAK/STAT), the phospholipase-C (PLC-γ) and the mitogen-activated protein kinase (MAPK) pathways. Moreover, it has been reported that cancer cases display an overactivation of c-KIT due to the presence of gain-of-function mutations or receptor overexpression, which renders c-KIT a tempting target for cancer treatment. In the case of male cancers the most documented activated pathways are the PI3-K and Src, both enhancing abnormal cell proliferation. It is also known that the Src activity in prostate cancer cases depends on the presence of tr-KIT, the cytoplasmic truncated variant of c-KIT that is specifically expressed in tumour tissues and, thus, a very interesting target for drug development. The present review provides an overview of the signalling pathways activated by SCF/c-KIT and discusses the potential application of c-KIT inhibitors for treatment of testicular and prostatic cancers.

Activated c-Kit receptor in the heart promotes cardiac repair and regeneration after injury

The role of endogenous c-Kit receptor activation on cardiac cell homeostasis and repair remains largely unexplored. Transgenic mice carrying an activating point mutation (TgD814Y) in the kinase domain of the c-Kit gene were generated. c-Kit^TgD814Y receptor was expressed in the heart during embryonic development and postnatal life, in a similar timing and expression pattern to that of the endogenous gene, but not in the hematopoietic compartment allowing the study of a cardiac-specific phenotype. c-Kit^TgD814Y mutation produced a constitutive active c-Kit receptor in cardiac tissue and cells from transgenic mice as demonstrated by the increased phosphorylation of ERK1/2 and AKT, which are the main downstream molecular effectors of c-Kit receptor signaling. In adult transgenic hearts, cardiac morphology, size and total c-Kit⁺ cardiac cell number was not different compared with wt mice. However, when c-Kit^TgD814Y mice were subjected to transmural necrotic heart damage by cryoinjury (CI), all transgenic survived, compared with half of wt mice. In the sub-acute phase after CI, transgenic and wt mice showed similar heart damage. However, 9 days after CI, transgenic mice exhibited an increased number of c-Kit⁺CD31⁺ endothelial progenitor cells surrounding the necrotic area. At later follow-up, a consistent reduction of fibrotic area, increased capillary density and increased cardiomyocyte replenishment rate (as established by BrdU incorporation) were observed in transgenic compared with wt mice. Consistently, CD45⁻c-Kit⁺ cardiac stem cells isolated from transgenic c-Kit^TgD814Y mice showed an enhanced endothelial and cardiomyocyte differentiation potential compared with cells isolated from the wt. Constitutive activation of c-Kit receptor in mice is associated with an increased cardiac myogenic and vasculogenic reparative potential after injury, with a significant improvement of survival.

Aloe-Emodin Induces Chondrogenic Differentiation of ATDC5 Cells via MAP Kinases and BMP-2 Signaling Pathways

Endochondral bone formation is the process by which mesenchymal cells condense into chondrocytes, which are ultimately responsible for new bone formation. The processes of chondrogenic differentiation and hypertrophy are critical for bone formation and are therefore highly regulated. The present study was designed to investigate the effect of aloe-emodin on chondrogenic differentiation in clonal mouse chondrogenic ATDC5 cells. Aloe-emodin treatment stimulated the accumulation of cartilage nodules in a dose-dependent manner. ATDC5 cells were treated with aloe-emodin and stained with alcian blue. Compared with the control cells, the ATDC5 cells showed more intense alcian blue staining. This finding suggested that aloe-emodin induced the synthesis of matrix proteoglycans and increased the activity of alkaline phosphatase. Aloe-emodin also enhanced the expressions of chondrogenic marker genes such as collagen II, collagen X, BSP and RunX2 in a time-dependent manner. Furthermore, examination of the MAPK signaling pathway showed that aloe-emodin increased the activation of extracellular signal-regulated kinase (ERK), but had no effect on p38 and c-jun N-terminal kinase (JNK). Aloe-emodin also enhanced the protein expression of BMP-2 in a time-dependent manner. Thus, these results showed that aloe-emodin exhibited chodromodulating effects via the BMP-2 or ERK signaling pathway. Aloe-emodin may have potential future applications for the treatment of growth disorders.

SCF/c-kit transactivates CXCR4-serine 339 phosphorylation through G protein-coupled receptor kinase 6 and regulates cardiac stem cell migration

C-kit positive cardiac stem cells (CSCs) have been shown to contribute to myocardial regeneration after infarction. Previously, we have shown that the c-kit ligand stem cell factor (SCF) can induce CSC migration into the infarcted area during myocardial infarction (MI). However, the precise mechanism involved is not fully understood. In this study, we found that CSCs also express C-X-C chemokine receptor type 4 (CXCR4), which is a typical member of the seven transmembrane-spanning G protein-coupled receptor (GPCR). In vitro, activation of c-kit signalling by SCF promotes migration of CSCs with increased phosphorylation of CXCR4-serine 339, p38 mitogen-activated protein kinase (p38 MAPK) and extracellular regulated protein kinases 1/2 (ERK1/2). Knockdown of CXCR4 expression by siRNA reduces SCF/c-kit-induced migration and downstream signalling. As previously reported, CXCR4-serine 339 phosphorylation is mainly regulated by GPCR kinase 6 (GRK6); thus, silencing of GRK6 expression by siRNA impairs CXCR4-serine 339 phosphorylation and migration of CSCs caused by SCF. In vivo, knockdown of GRK6 impairs the ability of CSCs to migrate into peri-infarcted areas. These results demonstrate that SCF-induced CSC migration is regulated by the transactivation of CXCR4-serine 339 phosphorylation, which is mediated by GRK6.

Daunorubicin Down-Regulates the Expression of Stem Cell Markers and Factors Involved in Stem Cell Migration and Homing in Rat Heart in Subchronic but not Acute Cardiomyopathy

We tested the hypothesis that daunorubicin (DAU) cardiotoxicity alters expression of cytokines involved in stem cell migration and homing. Male Wistar rats were treated with daunorubicin to induce acute DAU cardiomyopathy (6 × 3 mg/kg, i.p., every 48 hr, DAU-A) or subchronic DAU cardiomyopathy (15 mg/kg, i.v., DAU-C). The left ventricle was catheterized. The animals were killed 48 hr (DAU-A) and 8 weeks (DAU-C) after the last dose of DAU. Expression of foetal genes (Nppa, Nppb), isomyosins (Myh6, Myh7), sources of oxidative stress (Abcb8, gp91phox), cytokines (Sdf-1, Cxcr4, Scf, Vegf, Hgf, Igf-1), markers of cardiac progenitor (c-kit, Atnx-1), endothelial progenitor (CD34, CD133) and mesenchymal (CD44, CD105) stem cells were determined by qRT-PCR in left ventricular tissue. Reduced body-weight, decreased left ventricular weight and function, and elevated Nppa, Nppb, Myh7 were observed in both models. Myh6 decreased only in DAU-C, which had a 35% mortality. Up-regulated gp91phox and down-regulated Abcb8 in DAU were present only in DAU-C where we observed markedly decreased expressions of Scf and Vegf as well as expressions of stem cell markers. Down-regulation of cytokines and stem cell markers may reflect impaired chemotaxis, migration and homing of stem cells and tissue repair in the heart in subchronic but not acute model of DAU cardiomyopathy.

Crosstalk between SDF-1/CXCR4 and SDF-1/CXCR7 in cardiac stem cell migration

Stromal cell-derived factor 1 (SDF-1) is a chemokine that can be expressed in injured cardiomyocytes after myocardial infarction (MI). By combining with its receptor CXCR4, SDF-1 induced stem and progenitor cells migration. CXCR7, a novel receptor for SDF-1, has been identified recently. We aimed to explore the roles of SDF-1/CXCR4 and SDF-1/CXCR7 pathway and their crosstalk in CSCs migration. In the present study, CXCR4 and CXCR7 expression were identified in CSCs. Transwell assay showed that SDF-1 caused CSCs migration in a dose- and time-dependent manner, which could be significantly suppressed by CXCR4 or CXCR7 siRNA. Phospho-ERK, phospho-Akt and Raf-1 significantly elevated in CSCs with SDF-1 stimulation. Knockdown of CXCR4 or CXCR7 significantly decreased phospho-ERK or phospho-Akt, respectively, and eventually resulted in the inhibition of CSCs migration. Moreover, western blot showed that MK2206 (Akt inhibitor) increased the expression of phospho-ERK and Raf-1, whereas PD98059 (ERK inhibitor) had no effect on phospho-Akt and Raf-1. GW5074 (Raf-1 inhibitor) upregulated the expression of phospho-ERK, but had no effect on phospho-Akt. The present study indicated that SDF-1/CXCR7/Akt and SDF-1/CXCR4/ERK pathway played important roles in CSCs migration. Akt phosphorylation inhibited Raf-1 activity, which in turn dephosphorylated ERK and negatively regulated CSCs migration.

C-kit(+) resident cardiac stem cells improve left ventricular fibrosis in pressure overload

To investigate the effect of resident cardiac stem cells (RCSC) on myocardial remodeling, c-kit(+) RCSC were isolated from hearts of C57Bl/6-Tg (ACTb-EGFP)1Osb/J mice expressing green fluorescent protein and expanded in vitro. C57/Bl6N wildtype mice were subjected to transverse aortic constriction (TAC, 360 μm) or sham-operation. 5 × 10(5) c-kit(+) RCSC or c-kit(-) cardiac cells or cell buffer were infused intravenously 24 h post-surgery (n = 11-24 per group). Hypoxia-inducible factor-1α-mRNA in left ventricles of TAC mice was enhanced 24 h after transplantation. 35 days post-TAC, the density of c-kit(+) RCSC in the myocardium was increased by two-fold. Infusion of c-kit(+) resident cardiac stem cells post-TAC markedly reduced myocardial fibrosis and the expression of collagen Iα2 and connective tissue growth factor. Infusion of c-kit(-) cardiac cells did not ameliorate cardiac fibrosis. In parallel, expression of pro-angiogenic mediators (FGFb, IL-4, IL-6, TGFß, leptin) and the density of CD31(+) and CD31(+) GFP(+) endothelial cells were increased. Transplantation reduced brain- and atrial natriuretic peptides and the cardiomyocyte cross-sectional area. Infusion of c-kit(+) resident cardiac stem reduced the rate of apoptosis and oxidative stress in cardiomyocytes and in non-cardiomyocyte cells.

Activation of Notch1 signalling promotes multi-lineage differentiation of c-Kit(POS)/NKX2.5(POS) bone marrow stem cells: implication in stem cell translational medicine

Introduction

Transplantation of bone marrow mesenchymal stem cells (BMSCs) can repair injured hearts. However, whether BMSC populations contain cells with cardiac stem cell characteristics is ill-defined. We report here that Notch signalling can promote differentiation of c-Kit^POS/NKX2.5^POS BMSCs into cardiomyocyte-like cells.

Methods

Total BMSCs were isolated from Sprague–Dawley rat femurs and c-Kit^POS cells were purified. c-Kit^POS/NKX2.5^POS cells were isolated by single-cell cloning, and the presence of cardiomyocyte, smooth muscle cell (SMC), and endothelial cell differentiation markers assessed by immunofluorescence staining and semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis. Levels of c-Kit and Notch1–4 in total BMSCs and c-Kit^POS/NKX2.5^POS BMSCs were quantitated by flow cytometry. Following infection with an adenovirus over-expressing Notch1 intracellular domain (NICD), total BMSCs and c-Kit^POS/NKX2.5^POS cells were assessed for differentiation to cardiomyocyte, SMC, and endothelial cell lineages by immunofluorescence staining and real-time quantitative RT-PCR. Total BMSCs and c-Kit^POS/NKX2.5^POS cells were treated with the Notch1 ligand Jagged1 and markers of cardiomyocyte, SMC, and endothelial cell differentiation were examined by immunofluorescence staining and real-time quantitative RT-PCR analysis.

Results

c-Kit^POS/NKX2.5^POS cells were present among total BMSC populations, and these cells did not express markers of adult cardiomyocyte, SMC, or endothelial cell lineages. c-Kit^POS/NKX2.5^POS BMSCs exhibited a multi-lineage differentiation potential similar to total BMSCs. Following sorting, the c-Kit level in c-Kit^POS/NKX2.5^POS BMSCs was 84.4%. Flow cytometry revealed that Notch1 was the predominant Notch receptor present in total BMSCs and c-Kit^POS/NKX2.5^POS BMSCs. Total BMSCs and c-Kit^POS/NKX2.5^POS BMSCs overexpressing NICD had active Notch1 signalling accompanied by differentiation into cardiomyocyte, SMC, and endothelial cell lineages. Treatment of total BMSCs and c-Kit^POS/NKX2.5^POS BMSCs with exogenous Jagged1 activated Notch1 signalling and drove multi-lineage differentiation, with a tendency towards cardiac lineage differentiation in c-Kit^POS/NKX2.5^POS BMSCs.

Conclusions

c-Kit^POS/NKX2.5^POS cells exist in total BMSC pools. Activation of Notch1 signalling contributed to multi-lineage differentiation of c-Kit^POS/NKX2.5^POS BMSCs, favouring differentiation into cardiomyocytes. These findings suggest that modulation of Notch1 signalling may have potential utility in stem cell translational medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0085-2) contains supplementary material, which is available to authorized users.

Hyperhomocysteinemia regulated SCF expression in cultured cardiomyocytes via modulation of NF-κB activities

Hyperhomocysteinemia (HHcy) is an important, independent risk factor for coronary artery disease, especially for the myocardial infarction. Our previous study has shown that myocardial stem cell factor (SCF) mediated cardiac stem cells migration, which was involved in cardiac repair. However, it is not clear regarding the action of HHcy on the expression of SCF in cardiomyocytes. In the present study, cultured neonatal rat cardiomyocytes were treated with 20, 50, or 100 μM homocysteine (Hcy) for 5 h. Results showed an significantly increase of SCF expression with 20-50 μM Hcy incubation, which matched with elevated nuclear factor-kappaB (NF-κB) activities. Treatment with NF-κB inhibitor N-acetylcysteine significantly inhibited the increase of SCF. Nevertheless, 100 μM Hcy markedly decreased the expression of SCF, which was in accordance with the suppression of NF-κB activities. The present study indicated that HHcy regulated the expression of SCF in a concentration-dependent manner via modulation of NF-κB activities. Thus, HHcy may increase the risk for cardiovascular diseases not only by causing endothelial dysfunction but also by directly exerting detrimental effects on cardiomyocytes.

The modulation of cardiac progenitor cell function by hydrogel-dependent Notch1 activation

Myocardial infarction is the leading cause of death worldwide and phase I clinical trials utilizing cardiac progenitor cells (CPCs) have shown promising outcomes. Notch1 signaling plays a critical role in cardiac development and in the survival, cardiogenic lineage commitment, and differentiation of cardiac stem/progenitor cells. In this study, we functionalized self-assembling peptide (SAP) hydrogels with a peptide mimic of the Notch1 ligand Jagged1 (RJ) to evaluate the therapeutic benefit of CPC delivery in the hydrogels in a rat model of myocardial infarction. The behavior of CPCs cultured in the 3D hydrogels in vitro including gene expression, proliferation, and growth factor production was evaluated. Interestingly, we observed Notch1 activation to be dependent on hydrogel polymer density/stiffness with synergistic increase in presence of RJ. Our results show that RJ mediated Notch1 activation depending on hydrogel concentration differentially regulated cardiogenic gene expression, proliferation, and growth factor production in CPCs in vitro. In rats subjected to experimental myocardial infarction, improvement in acute retention and cardiac function was observed following cell therapy in RJ hydrogels compared to unmodified or scrambled peptide containing hydrogels. This study demonstrates the potential therapeutic benefit of functionalizing SAP hydrogels with RJ for CPC based cardiac repair.

SCF/C-KIT signaling modulates tryptase expression in acute myeloid leukemia cells

Tryptase is a serine protease with a variety of biological functions. Recently, elevated serum tryptase has been detected in certain patients with acute myeloid leukemia (AML). However, the underlying mechanism for the regulation of tryptase expression remains elusive. In this study, we aimed to investigate the role of stem cell factor (SCF)/C-KIT signaling in regulating the expression of tryptase in AML cells. We found a significant positive correlation between tryptase and C-KIT expression levels in AML patients. Furthermore, real-time PCR, Western blot and ELISA analysis showed that SCF upregulated tryptase mRNA and protein expression in U937 cells, and that this effect was abolished by pretreatment with PD98059 and SB230580. In addition, levels of phosphorylated ERK1/2 and p38MAPK correlated with tryptase levels. Taken together, these data suggest that the expression of tryptase is regulated by SCF/C-KIT signaling via the ERK1/2 and p38MAPK pathways.

SCF increases cardiac stem cell migration through PI3K/AKT and MMP‑2/‑9 signaling

The transplantation of cardiac stem cells (CSCs) is thought to be responsible for improving the performance of injured heart induced by myocardial infarction (MI). However, the mechanisms involved in the migration of activated CSCs post-MI remain to be clarified. In this study, CSCs were isolated from rat hearts and a cellular migration assay was performed using a 24-well Transwell system. Stem cell factor (SCF) induced CSC migration in a concentration-dependent manner, which could be blocked with an SCF antibody as well as a PI3K/AKT inhibitor, LY294002. Moreover, SCF induced the expression and activity of matrix metalloproteinase (MMP)-2 and MMP-9 in a concentration- and time-dependent manner, as measured by quantitative RT-PCR, western blot analysis and gelatin zymography. Results of western blot analysis revealed phosphorylated AKT was markedly increased in SCF-treated CSCs and that inhibition of SCF/c-Kit signaling or phospho-AKT activity significantly attenuated the SCF-induced expression of MMP-2 and MMP-9. Thus, our results showed that SCF partially mediated CSC migration via the activation of PI3K/AKT/MMP-2/-9 signaling.

Migration of resident cardiac stem cells in myocardial infarction

Ischemic heart disease is a major cause of morbidity and mortality worldwide. Stem cell-based therapy, which aims to restore cardiac structure and function by regeneration of functional myocardium, has recently been proposed as a novel alternative treatment modality. Resident cardiac stem cells (CSCs) in adult hearts are a key cell type under investigation. CSCs have been shown to be able to repair damaged myocardium and improve myocardial function in both human and animal studies. This approach relies not only on the proliferation of the CSCs, but also upon their migration to the site of injury within the heart. Here, we briefly review reported CSC populations and discuss signaling factors and pathways required for the migration of CSCs.

Local activation of cardiac stem cells for post-myocardial infarction cardiac repair

The prognosis of patients with myocardial infarction (MI) and resultant chronic heart failure remains extremely poor despite continuous advancements in optimal medical therapy and interventional procedures. Animal experiments and clinical trials using adult stem cell therapy following MI have shown a global improvement of myocardial function. The emergence of stem cell transplantation approaches has recently represented promising alternatives to stimulate myocardial regeneration. Regarding their tissue-specific properties, cardiac stem cells (CSCs) residing within the heart have advantages over other stem cell types to be the best cell source for cell transplantation. However, time-consuming and costly procedures to expanse cells prior to cell transplantation and the reliability of cell culture and expansion may both be major obstacles in the clinical application of CSC-based transplantation therapy after MI. The recognition that the adult heart possesses endogenous CSCs that can regenerate cardiomyocytes and vascular cells has raised the unique therapeutic strategy to reconstitute dead myocardium via activating these cells post-MI. Several strategies, such as growth factors, mircoRNAs and drugs, may be implemented to potentiate endogenous CSCs to repair infarcted heart without cell transplantation. Most molecular and cellular mechanism involved in the process of CSC-based endogenous regeneration after MI is far from understanding. This article reviews current knowledge opening up the possibilities of cardiac repair through CSCs activation in situ in the setting of MI.

Stem Cell Factor Receptor/c-Kit: From Basic Science to Clinical Implications

Stem cell factor (SCF) is a dimeric molecule that exerts its biological functions by binding to and activating the receptor tyrosine kinase c-Kit. Activation of c-Kit leads to its autophosphorylation and initiation of signal transduction. Signaling proteins are recruited to activated c-Kit by certain interaction domains (e.g., SH2 and PTB) that specifically bind to phosphorylated tyrosine residues in the intracellular region of c-Kit. Activation of c-Kit signaling has been found to mediate cell survival, migration, and proliferation depending on the cell type. Signaling from c-Kit is crucial for normal hematopoiesis, pigmentation, fertility, gut movement, and some aspects of the nervous system. Deregulated c-Kit kinase activity has been found in a number of pathological conditions, including cancer and allergy. The observation that gain-of-function mutations in c-Kit can promote tumor formation and progression has stimulated the development of therapeutics agents targeting this receptor, e.g., the clinically used inhibitor imatinib mesylate. Also other clinically used multiselective kinase inhibitors, for instance, sorafenib and sunitinib, have c-Kit included in their range of targets. Furthermore, loss-of-function mutations in c-Kit have been observed and shown to give rise to a condition called piebaldism. This review provides a summary of our current knowledge regarding structural and functional aspects of c-Kit signaling both under normal and pathological conditions, as well as advances in the development of low-molecular-weight molecules inhibiting c-Kit function.

Overexpression of SDF-1α enhanced migration and engraftment of cardiac stem cells and reduced infarcted size via CXCR4/PI3K pathway

Cardiac stem cells (CSCs) can home to the infarcted area and regenerate myocardium. Stromal cell-derived factor-1α/C-X-C chemokine receptor type 4 (SDF-1α/CXCR4) axis is pivotal in inducing CSCs migration. However, the mechanisms remain unclear. This study set out to detect if SDF-1α promotes migration and engraftment of CSCs through the CXCR4/PI3K (phosphatidylinositol 3-kinase) pathway. In the in vitro experiment, c-kit+ cells were isolated from neonatal mouse heart fragment culture by magnetic cell sorting. Fluorescence-activated cell sorting results demonstrated that a few c-kit+ cells expressed CD45 (4.54%) and Sca-1 (2.58%), the hematopoietic stem cell marker. Conditioned culture could induce c-kit+ cells multipotent differentiation, which was confirmed by cardiac troponin I (cTn-I), α-smooth muscle actin (α-SMA), and von Willebrand factor (vWF) staining. In vitro chemotaxis assays were performed using Transwell cell chambers to detect CSCs migration. The results showed that the cardiomyocytes infected with rAAV1-SDF-1α-eGFP significantly increased SDF-1α concentration, 5-fold more in supernatant than that in the control group, and subsequently attracted more CSCs migration. This effect was diminished by administration of AMD3100 (10 µg/ml, CXCR4 antagonist) or LY294002 (20 µmol/L, PI3K inhibitor). In myocardial infarction mice, overexpression of SDF-1α in the infarcted area by rAAV1-SDF-1α-eGFP infection resulted in more CSCs retention to the infarcted myocardium, a higher percentage of proliferation, and reduced infarcted area which was attenuated by AMD3100 or ly294002 pretreatment. These results indicated that overexpression of SDF-1α enhanced CSCs migration in vitro and engraftment of transplanted CSCs and reduced infarcted size via CXCR4/PI3K pathway.

Hyperglycemia suppresses cardiac stem cell homing to peri-infarcted myocardium via regulation of ERK1/2 and p38 MAPK activities

Hyperglycemia in the acute phase of myocardial infarction (MI) is a marker of worse prognosis in both diabetic and non-diabetic patients; however, the role of hyperglycemia in the homing of cardiac stem cells (CSCs) to damaged myocardium post-MI and the possible mechanisms involved are not well understood. In this study, an MI model was induced in normoglycemic and hyperglycemic rats by left coronary artery ligation. Immunofluorescence was used to examine the migration of CSCs in vivo by injecting BrdU-labeled CSCs into the atrium-ventricle groove (AV-groove). Immunohistochemistry, western blot analysis and ELISA were carried out to detect the expression of stem cell factor (SCF) protein and RT-PCR was conducted for the expression of SCF mRNA. Phosphorylation of ERK1/2 and p38 MAPK was detected by western blot analysis. Afterwards, cardiac function was evaluated by hemodynamic measurement. On Day 5 post-MI, the accumulation of CSCs significantly increased in the peri-infarcted myocardium in normoglycemic rats, which led to an improvement in cardiac function 3 weeks after MI. However, the accumulation of CSCs markedly decreased in hyperglycemic rats, followed by the decline of cardiac function. SCF expression, followed with phosphorylation of ERK1/2 and p38 MAPK, were also significantly downregulated in the peri-infarcted myocardium in hyperglycemic rats compared to normoglycemic rats. Moreover, SCF expression and the migration of CSCs were blocked by either the MEK-specific inhibitor PD98059 or the p38 MAPK-selective inhibitor SB203580. The experiments in vitro confirmed that hyperglycemia decreased SCF expression via reduction in ERK1/2 and p38 MAPK activities and further inhibited the migration of CSCs. The results suggest that hyperglycemia suppresses CSC migration towards the ischemic area post-MI. This is possibly due to decreased myocardial SCF expression via reduction of ERK1/2 and p38 MAPK activities in hyperglycemic rats.

Stem cell factor gene transfer promotes cardiac repair after myocardial infarction via in situ recruitment and expansion of c-kit+ cells

RATIONALE

There is growing evidence that the myocardium responds to injury by recruiting c-kit(+) cardiac progenitor cells to the damage tissue. Even though the ability of exogenously introducing c-kit(+) cells to injured myocardium has been established, the capability of recruiting these cells through modulation of local signaling pathways by gene transfer has not been tested.

OBJECTIVE

To determine whether stem cell factor gene transfer mediates cardiac regeneration in a rat myocardial infarction model, through survival and recruitment of c-kit(+) progenitors and cell-cycle activation in cardiomyocytes, and explore the mechanisms involved.

METHODS AND RESULTS

Infarct size, cardiac function, cardiac progenitor cells recruitment, fibrosis, and cardiomyocyte cell-cycle activation were measured at different time points in controls (n=10) and upon stem cell factor gene transfer (n=13) after myocardial infarction. We found a regenerative response because of stem cell factor overexpression characterized by an enhancement in cardiac hemodynamic function: an improvement in survival; a reduction in fibrosis, infarct size and apoptosis; an increase in cardiac c-kit(+) progenitor cells recruitment to the injured area; an increase in cardiomyocyte cell-cycle activation; and Wnt/β-catenin pathway induction.

CONCLUSIONS

Stem cell factor gene transfer induces c-kit(+) stem/progenitor cell expansion in situ and cardiomyocyte proliferation, which may represent a new therapeutic strategy to reverse adverse remodeling after myocardial infarction.

Pressure overload leads to an increase of cardiac resident stem cells

Recent studies suggest that the mammalian heart possesses some capacity for cardiac regeneration. This regenerative capacity is primarily documented postnatally and after myocardial infarction or pressure overload. Although the cell type that mediates endogenous regeneration is unclear, cardiac stem cells might be considered as potential candidates. To determine the number of c-kit + cardiac resident cells under conditions of pressure overload, we evaluated specimens derived from n = 8 patients with pressure overloaded single right ventricles in comparison to n = 4 explanted hearts from patients with dilated cardiomyopathy and n = 14 biopsies from children after heart transplantation. The age of the patients ranged from 16 days to 19 years. For quantification of cardiac stem cells, c-kit+/mast cell tryptase-/CD45- cells were counted and expressed as percent of the total nuclei. In specimens from patients with dilated cardiomyopathy, 0.13 ± 0.09% c-kit +/mast cell tryptase-/CD45- cells were detected. However, in specimens from patients with pressure overloaded single right ventricles, the numbers of c-kit+/mast cell tryptase-/CD45- cells were significantly higher (0.41 ±0.24%, p < 0.05). Under conditions of pressure overload, the right ventricle shows an approximately three-fold increase in c-kit+/mast cell tryptase-/CD45- cardiac resident cells. Despite the fact that this increased number of c-kit+ cells is not sufficient to prevent the failing heart from congestive heart failure, understanding the mechanism that leads to an increase of presumably cardiac resident stem cells under conditions of pressure overload might help to develop new strategies to enhance endogenous repair.

Hematopoietic cytokines for cardiac repair: mobilization of bone marrow cells and beyond

Hematopoietic cytokines, traditionally known to influence cellular proliferation, differentiation, maturation, and lineage commitment in the bone marrow, include granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor, stem cell factor, Flt-3 ligand, and erythropoietin among others. Emerging evidence suggests that these cytokines also exert multifarious biological effects on diverse nonhematopoietic organs and tissues. Although the precise mechanisms remain unclear, numerous studies in animal models of myocardial infarction (MI) and heart failure indicate that hematopoietic cytokines confer potent cardiovascular benefits, possibly through mobilization and subsequent homing of bone marrow-derived cells into the infarcted heart with consequent induction of myocardial repair involving multifarious mechanisms. In addition, these cytokines are also known to exert direct cytoprotective effects. However, results from small-scale clinical trials of G-CSF therapy as a single agent after acute MI have been discordant and largely disappointing. It is likely that cardiac repair following cytokine therapy depends on a number of known and unknown variables, and further experimental and clinical studies are certainly warranted to accurately determine the true therapeutic potential of such therapy. In this review, we discuss the biological features of several key hematopoietic cytokines and present the basic and clinical evidence pertaining to cardiac repair with hematopoietic cytokine therapy.

Hyperhomocysteinemia inhibited cardiac stem cell homing into the peri-infarcted area post myocardial infarction in rats

BACKGROUND

Hyperhomocysteinemia (HHcy) has been reported as an independent risk factor for coronary artery disease; however it is not clear regarding the action of HHcy on the homing of cardiac stem cells (CSCs) to the damaged myocardium and the consequent CSCs-mediated cardiac repair post myocardial infarction.

METHODS

Sprague-Dawley (SD) rats were divided into 4 groups. HHcy was induced in the rats by a 6-week high-methionine diet. Rat heart MI model was developed by left coronary artery ligation. Immunofluorescence was used to examine the CSCs migration in vivo via injecting BrdU-labeled CSCs into AV-groove followed by a coronary ligation. Immunohistochemistry, western blot and ELISA analysis were carried out to detect the expression of stem cell factor (SCF) protein, and RT-PCR was conducted for the expression of SCF mRNA.

RESULTS

On day 5 of MI model creation, accumulation of CSCs was significantly increased in the peri-infarcted area by the non-hyperhomocysteinemic rats, which led to an improvement of cardiac function at 3 weeks after MI. however, the accumulation of CSCs was markedly decreased by the hyperhomocysteinemic rats followed with the decline of cardiac function. SCF expression was also significantly decreased in the peri-infarcted area by the hyperhomocysteinemic rats compared to the non-hyperhomocysteinemic rats. The experiments in vitro confirmed that homocysteine (Hcy) decreased SCF expression via inhibition of TNF-α-induced activity of NF-κB, further reduced the migration of CSCs.

CONCLUSION

It demonstrated that hyperhomocysteinemia may significantly contribute to restrain CSCs-mediated cardiac repair by reducing SCF-induced homing of CSCs.

SDF-1α/CXCR4 axis is involved in glucose-potentiated proliferation and chemotaxis in rat vascular smooth muscle cells

Excessive proliferation of vascular smooth muscle cells (VSMCs), which migrate from the tunica media to the subendothelial region, is one of the primary lesions involved in atherogenesis in diabetes. Here, we investigated whether high glucose potentiated the proliferation and chemotaxis of VSMCs by activating SDF-1α/CXCR4/PI-3K/Akt signalling. The expression of SDF-1α, CXCR4 and PCNA was up-regulated in tunica media of thoracic aortas by streptozotocin-induced hyperglycaemic Sprague-Dawley rats. Exposure of primary VSMCs to high glucose (25 mM) led to the up-regulated expression of SDF-1α and CXCR4, activated PI-3K/Akt signalling, and consequently promoted the proliferation and chemotaxis of VSMCs. Interestingly, the administration of SDF-1 siRNA or neutralizing antibody against SDF-1α abolished high glucose-induced up-regulation of CXCR4. Moreover, pretreatment with SDF-1α neutralizing antibody, CXCR4 specific inhibitor (AMD3100) or PI-3K inhibitor (LY294002) attenuated the high glucose-potentiated proliferation and chemotaxis in VSMCs. These results suggested that high glucose activated the SDF-1α/CXCR4/PI-3K/Akt signalling pathway in VSMCs in an autocrine manner, which enhanced the proliferation and chemotaxis of VSMCs.