Bone Marrow Niche in Cardiometabolic Disease: Mechanisms and Therapeutic Potential

Cardiovascular and cardiometabolic diseases are leading causes of morbidity and mortality worldwide, driven in part by chronic inflammation. Emerging research suggests that the bone marrow microenvironment, or marrow niche, plays a critical role in both immune system regulation and disease progression. The bone marrow niche is essential for maintaining hematopoietic stem cells (HSCs) and orchestrating hematopoiesis. Under normal conditions, this niche ensures a return to immune homeostasis after acute stress. However, in the setting of inflammatory conditions such as those seen in cardiometabolic diseases, it becomes dysregulated, leading to enhanced myelopoiesis and immune activation. This review explores the reciprocal relationship between the bone marrow niche and cardiometabolic diseases, highlighting how alterations in the niche contribute to disease development and progression. The niche regulates HSCs through complex interactions with stromal cells, endothelial cells, and signaling molecules. However, in the setting of chronic diseases such as hypertension, atherosclerosis, and diabetes, inflammatory signals disrupt the balance between HSC self-renewal and differentiation, promoting the excessive production of proinflammatory myeloid cells that exacerbate the disease. Key mechanisms discussed include the effects of hyperlipidemia, hyperglycemia, and sympathetic nervous system activation on HSC proliferation and differentiation. Furthermore, the review emphasizes the role of epigenetic modifications and metabolic reprogramming in creating trained immunity, a phenomenon whereby HSCs acquire long-term proinflammatory characteristics that sustain disease states. Finally, we explore therapeutic strategies aimed at targeting the bone marrow niche to mitigate chronic inflammation and its sequelae. Novel interventions that modulate hematopoiesis and restore niche homeostasis hold promise for the treatment of cardiometabolic diseases. By interrupting the vicious cycle of inflammation and marrow dysregulation, such therapies may offer new avenues for reducing cardiovascular risk and improving patient outcomes.

Axin2 depletion in macrophages alleviated senescence and increased immune response after myocardial infarction

OBJECTIVE AND DESIGN

This study aimed to investigate Axin2 effects on myocardial infarction (MI) using a macrophage Axin2 conditional knockout (cKO) mouse model, RAW264.7 cell line, and human subepicardial tissues from patients with coronary artery bypass graft (CABG).

MATERIAL OR SUBJECTS

Axin2 cKO mice showed decreased cardiac function, reduced edema, increased lymphangiogenesis, and improved repair in MI Few studies border zones. Hypoxic macrophages with Axin2 depletion exhibited decreased senescence, elevated IL6 expression, and increased LYVE1 transcription. Senescent macrophages decreased in patients with CABG and low Axin2 expression.

TREATMENT

Treatment options included in this study were MI induction in Axin2 cKO mice, in vitro experiments with RAW264.7 cells, and analysis of human subepicardial tissues.

METHODS

Assays included MI induction, in vitro experiments, and tissue analysis with statistical tests applied.

RESULTS

Axin2 cKO improved cardiac function, reduced edema, enhanced lymphangiogenesis, and decreased senescence. Hypoxic macrophages with Axin2 depletion showed reduced senescence, increased IL6 expression, and elevated LYVE1 transcription. Senescent macrophages decreased in patients with CABG and low Axin2 expression.

CONCLUSION

Targeting Axin2 emerges as a novel therapeutic strategy for regulating cardiac lymphatics and mitigating cell senescence post-MI, evidenced by improved outcomes in Axin2-deficient conditions.

Reduced hematopoietic-inflammatory response and worse outcomes in patients with recurrent myocardial infarction in comparison with primary myocardial infarction

BACKGROUND

Recurrent myocardial infarction (RMI) portends an unfavorable outcome, which might be related to diminished hematopoietic-inflammatory activation. We aimed to investigate the hematopoietic-inflammatory activation and the outcome in categorized patients with primary myocardial infarction (PMI) versus RMI as well as chronic stable angina (CSA) by 18F-FDG PET.

RESULTS

A total of 105 patients (88 males; 60.1 ± 9.7 years) were included. Target-to-background ratio of bone marrow (TBRBM) was highest in the PMI group (n = 45), intermediate in the RMI group (n = 30), and lowest in the CSA group (n = 30) (P < 0.001). RMI group exhibited larger scar, significantly reduced left ventricular ejection fraction, and enlarged end systolic volume in comparison with the PMI and CSA groups, respectively (P < 0.05). Additionally, there was a significantly positive correlation between TBRBM and TBRaorta (P < 0.001). The cumulative major adverse cardiac events free survival of patients in the RMI group was lower than that in the PMI and CSA groups during a median follow-up of 16.6 months (P = 0.026).

CONCLUSIONS

RMI conferred relatively decreased hematopoietic-inflammatory activation compared with PMI. Patients with RMI presented subsequent enlarged myocardial scar, worsened cardiac dysfunction, aggravated remodeling, and worse outcomes than that in PMI patients.

Imaging increased metabolism in the spinal cord in mice after middle cerebral artery occlusion

Emerging evidence indicates crosstalk between the brain and hematopoietic system following cerebral ischemia. Here, we investigated metabolism and oxygenation in the spleen and spinal cord in a transient middle cerebral artery occlusion (tMCAO) model. Sham-operated and tMCAO mice underwent [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) to assess glucose metabolism. Naïve, sham-operated and tMCAO mice underwent multispectral optoacoustic tomography (MSOT) assisted by quantitative model-based reconstruction and unmixing algorithms for accurate mapping of oxygenation patterns in peripheral tissues at 24 h after reperfusion. We found increased [18F]FDG uptake and reduced MSOT oxygen saturation, indicating hypoxia in the thoracic spinal cord of tMCAO mice compared with sham-operated mice but not in the spleen. Reduced spleen size was observed in tMCAO mice compared with sham-operated mice ex vivo. tMCAO led to an increase in the numbers of mature T cells in femoral bone marrow tissues, concomitant with a stark reduction in these cell subsets in the spleen and peripheral blood. The combination of quantitative PET and MSOT thus enabled observation of hypoxia and increased metabolic activity in the spinal cord of tMCAO mice at 24 h after occlusion compared to sham-operated mice.

Quo Vadis? Immunodynamics of Myeloid Cells after Myocardial Infarction

Myocardial infarction (MI), a major contributor to worldwide morbidity and mortality, is caused by a lack of blood flow to the heart. Affected heart tissue becomes ischemic due to deficiency of blood perfusion and oxygen delivery. In case sufficient blood flow cannot be timely restored, cardiac injury with necrosis occurs. The ischemic/necrotic area induces a systemic inflammatory response and hundreds of thousands of leukocytes are recruited from the blood to the injured heart. The blood pool of leukocytes is rapidly depleted and urgent re-supply of these cells is needed. Myeloid cells are generated in the bone marrow (BM) and spleen, released into the blood, travel to sites of need, extravasate and accumulate inside tissues to accomplish various functions. In this review we focus on the "leukocyte supply chain" and will separately evaluate different myeloid cell compartments (BM, spleen, blood, heart) in steady state and after MI. Moreover, we highlight the local and systemic kinetics of extracellular factors, chemokines and danger signals involved in the regulation of production/generation, release, transportation, uptake, and activation of myeloid cells during the inflammatory phase of MI.

Blockade of Wnt Secretion Attenuates Myocardial Ischemia-Reperfusion Injury by Modulating the Inflammatory Response

Wnt (a portmanteau of Wingless and Int-1) signaling in the adult heart is largely quiescent. However, there is accumulating evidence that it gets reactivated during the healing process after myocardial infarction (MI). We here tested the therapeutic potential of the Wnt secretion inhibitor LGK-974 on MI healing. Ischemia/reperfusion (I/R) injury was induced in mice and Wnt signaling was inhibited by oral administration of the porcupine inhibitor LGK-974. The transcriptome was analyzed from infarcted tissue by using RNA sequencing analysis. The inflammatory response after I/R was evaluated by flow cytometry. Heart function was assessed by echocardiography and fibrosis by Masson's trichrome staining. Transcriptome and gene set enrichment analysis revealed a modulation of the inflammatory response upon administration of the Wnt secretion inhibitor LGK-974 following I/R. In addition, LGK-974-treated animals showed an attenuated inflammatory response and improved heart function. In an in vitro model of hypoxic cardiomyocyte and monocyte/macrophage interaction, LGK974 inhibited the activation of Wnt signaling in monocytes/macrophages and reduced their pro-inflammatory phenotype. We here show that Wnt signaling affects inflammatory processes after MI. The Wnt secretion inhibitor LGK-974 appears to be a promising compound for future immunomodulatory approaches to improve cardiac remodeling after MI.

Immune and Inflammatory Networks in Myocardial Infarction: Current Research and Its Potential Implications for the Clinic

Despite recent scientific and technological advances, myocardial infarction (MI) still represents a major global health problem, leading to high morbidity and mortality worldwide. During the post-MI wound healing process, dysregulated immune inflammatory pathways and failure to resolve inflammation are associated with maladaptive left ventricular remodeling, progressive heart failure, and eventually poor outcomes. Given the roles of immune cells in the host response against tissue injury, understanding the involved cellular subsets, sources, and functions is essential for discovering novel therapeutic strategies that preserve the protective immune system and promote optimal healing. This review discusses the cellular effectors and molecular signals across multi-organ systems, which regulate the inflammatory and reparative responses after MI. Additionally, we summarize the recent clinical and preclinical data that propel conceptual revolutions in cardiovascular immunotherapy.

LINC00936 exacerbated myocardial infarction progression via miR-4795-3p/Wnt3a signaling pathway based on biological and imaging methods

OBJECTIVE

LncRNAs show great potential in diagnosing and treating myocardial infarction (MI). Clarifying the mechanism of lncRNAs on MI is of great significance for the application of MI biomarkers. Therefore, this report intended to determine the role and mechanism of LINC00936 on MI by biological and imaging methods.

METHODS

Hypoxia H9C2 model was established by hypoxia treatment. Flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling assay detected the apoptosis of H9C2. H2DCFDA staining and enzyme-linked immunosorbent assay (ELISA) was used to detect the reactive oxygen species (ROS) accumulation and Lactate dehydrogenase (LDH) contents, respectively. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to detect LINC00936, Wnt3a and miR-4795-3p levels. Western blot detected Wnt3a protein expression. Dual luciferase reporter assays detected the relationship of miR-4795-3p to LINC00936 or Wnt3a. Echocardiography analysis detected cardiac function. 2,3,5-Triphenyltetrazolium chloride (TTC) detected the infarct size. Masson staining detected the pathological changes.

RESULTS

LINC00936 level was elevated in the MI patients compared with the controls. Overexpression of LINC00936 promoted apoptosis and ROS accumulation in hypoxia H9C2 model and exacerbated MI progression in vivo. miR-4795-3p bound with LINC00936 in H9C2 cells and miR-4795-3p mimics inhibited apoptosis and ROS accumulation in hypoxia H9C2 model regulated by LINC00936. Wnt3a was targeted by miR-4795-3p and Wnt3a elevation promoted apoptosis and ROS accumulation in hypoxia H9C2 model.

CONCLUSION

In this report, we illustrated that LINC00936 exacerbated MI progression via the miR-4795-3p/Wnt3a signaling pathway based on biological and imaging methods. These findings might provide potential molecular target for the diagnosis and treatment of MI.

Diverse cellular origins of adult blood vascular endothelial cells

During embryonic stages, vascular endothelial cells (ECs) originate from the mesoderm, at specific extraembryonic and embryonic regions, through a process called vasculogenesis. In the adult, EC renewal/replacement mostly depend on local resident ECs or endothelial progenitor cells (EPCs). Nevertheless, contribution from circulating ECs/EPCs was also reported. In addition, cells lacking from EC/EPC markers with in vitro extended plasticity were shown to originate endothelial-like cells (ELCs). Most of these cells consist of mesenchymal stromal progenitors, which would eventually get mobilized from the bone marrow after injury. Based on that, current knowledge on different mouse and human bone marrow stromal cell (BM-SC) subpopulations, able to contribute with mesenchymal stromal/stem cells (MSCs), is herein reviewed. Such analyses underline an unexpected heterogeneity among sinusoidal LepR⁺ stromal/CAR cells. For instance, in a recent report a subgroup of LepR⁺ stromal/CAR progenitors, which express GLAST and is traced in Wnt1^Cre;R26R^Tom mice, was found to contribute with ELCs in vivo. These GLAST ​⁺ ​Wnt1⁺ BM-SCs were shown to get mobilized to the peripheral blood and to contribute with liver regeneration. Other sources of ELCs, such as adipose, neural and dental pulp tissues, were also published. Finally, mechanisms likely involved in the enhanced cellular plasticity properties of bone marrow/adipose tissue stromal cells, able to originate ELCs, are assessed. In the future, strategies to analyze the in vivo expression profile of stromal cells, with MSC properties, in combination with screening of active genomic regions at the single cell-level, during early postnatal development and/or after injury, will likely help understanding properties of these ELC sources.

Hematopoiesis and Cardiovascular Disease

A central feature of atherosclerosis, the most prevalent chronic vascular disease and root cause of myocardial infarction and stroke, is leukocyte accumulation in the arterial wall. These crucial immune cells are produced in specialized niches in the bone marrow, where a complex cell network orchestrates their production and release. A growing body of clinical studies has documented a correlation between leukocyte numbers and cardiovascular disease risk. Understanding how leukocytes are produced and how they contribute to atherosclerosis and its complications is, therefore, critical to understanding and treating the disease. In this review, we focus on the key cells and products that regulate hematopoiesis under homeostatic conditions, during atherosclerosis and after myocardial infarction.

Clonal hematopoiesis driven by somatic mutations: A new player in atherosclerotic cardiovascular disease

The accumulation of acquired mutations is an inevitable consequence of the aging process, but its pathophysiological relevance has remained largely unexplored beyond cancer. Most of these mutations have little or no functional consequences, but in a few rare instances, a mutation may arise that confers a competitive advantage to a stem cell, leading to its clonal expansion. When such a mutation occurs in hematopoietic stem cells, it leads to a situation of clonal hematopoiesis, which has the potential to affect multiple tissues beyond the bone marrow, as the clonal expansion of the mutant stem cell is extended to circulating blood cells and tissue-infiltrating immune cells. Recent genomics and experimental studies have provided support to the notion that this somatic mutation-driven clonal hematopoiesis contributes to vascular inflammation and the development of atherosclerosis and related cardiovascular and cerebrovascular ischemic events. Here, we review our current understanding of this emerging cardiovascular risk modifier and the mechanisms underlying its connection to atherosclerosis development.

Angiogenic Abnormalities in Diabetes Mellitus: Mechanistic and Clinical Aspects

CONTEXT

Diabetes causes severe pathological changes to the microvasculature in many organs and tissues and is at the same time associated with an increased risk of coronary and peripheral macrovascular events. We herein review alterations in angiogenesis observed in human and experimental diabetes and how they contribute to diabetes onset and development of vascular complications.

EVIDENCE ACQUISITION

The English language medical literature was searched for articles reporting on angiogenesis/vasculogenesis abnormalities in diabetes and their clinical manifestations, mechanistic aspects, and possible therapeutic implications.

EVIDENCE SYNTHESIS

Angiogenesis is a complex process, driven by a multiplicity of molecular mechanisms and involved in several physiological and pathological conditions. Incompetent angiogenesis is pervasive in diabetic vascular complications, with both excessive and defective angiogenesis observed in various tissues. A striking different angiogenic response typically occurs in the retina vs the myocardium and peripheral circulation, but some commonalities in abnormal angiogenesis can explain the well-known association between microangiopathy and macroangiopathy. Impaired angiogenesis can also affect endocrine islet and adipose tissue function, providing a link to diabetes onset. Exposure to high glucose itself directly affects angiogenic/vasculogenic processes, and the mechanisms include defective responses to hypoxia and proangiogenic factors, impaired nitric oxide bioavailability, shortage of proangiogenic cells, and loss of pericytes.

CONCLUSIONS

Dissecting the molecular drivers of tissue-specific alterations of angiogenesis/vasculogenesis is an important challenge to devise new therapeutic approaches. Angiogenesis-modulating therapies should be carefully evaluated in view of their potential off-target effects. At present, glycemic control remains the most reasonable therapeutic strategy to normalize angiogenesis in diabetes.

Influence of Local Myocardial Infarction on Endothelial Function, Neointimal Progression, and Inflammation in Target and Non-Target Vascular Territories in a Porcine Model of Acute Myocardial Infarction

BACKGROUND

Patients with acute myocardial infarction (AMI) have worse clinical outcomes than those with stable coronary artery disease despite revascularization. Non-culprit lesions of AMI also involve more adverse cardiovascular events. This study aimed to investigate the influence of AMI on endothelial function, neointimal progression, and inflammation in target and non-target vessels.

METHODS

In castrated male pigs, AMI was induced by balloon occlusion and reperfusion into the left anterior descending artery (LAD). Everolimus-eluting stents (EES) were implanted in the LAD and left circumflex (LCX) artery 2 days after AMI induction. In the control group, EES were implanted in the LAD and LCX in a similar fashion without AMI induction. Endothelial function was assessed using acetylcholine infusion before enrollment, after the AMI or sham operation, and at 1 month follow-up. A histological examination was conducted 1 month after stenting.

RESULTS

A total of 10 pigs implanted with 20 EES in the LAD and LCX were included. Significant paradoxical vasoconstriction was assessed after acetylcholine challenge in the AMI group compared with the control group. In the histologic analysis, the AMI group showed a larger neointimal area and larger area of stenosis than the control group after EES implantation. Peri-strut inflammation and fibrin formation were significant in the AMI group without differences in injury score. The non-target vessel of the AMI also showed similar findings to the target vessel compared with the control group.

CONCLUSION

In the pig model, AMI events induced endothelial dysfunction, inflammation, and neointimal progression in the target and non-target vessels.

The role of Wnt signaling in the healing myocardium: a focus on cell specificity

Various cell types are involved in the healing process after myocardial infarction (MI). Besides cardiac resident cells (such as cardiomyocytes, fibroblasts and endothelial cells) already present at the lesion site, a massive influx of leukocytes (mainly monocytes and neutrophils) is observed within hours after the ischemic event. So far, little is known about modes of interaction of these cells. Wnt signaling is an evolutionary conserved signaling cassette known to play an important role in cell-cell communication. While the overall reactivation of Wnt signaling upon ischemic injury is well described, the precise expression pattern of Wnt proteins, however, is far from understood. We here describe known Wnt components that partake in MI healing and differentiate cell-specific aspects. The secretion of Wnt proteins and their antagonists in the context of cardiac inflammation after MI appear to be tightly regulated in a spatial-temporal manner. Overall, we aim to stress the importance of elucidating not only Wnt component-specific aspects, but also their sometimes contradicting effects in different target cells. A better understanding of Wnt signaling in MI healing may eventually lead to the development of successful therapeutic approaches in an often considered "un-druggable" pathway.

Monocyte and haematopoietic progenitor reprogramming as common mechanism underlying chronic inflammatory and cardiovascular diseases

A large number of cardiovascular events are not prevented by current therapeutic regimens. In search for additional, innovative strategies, immune cells have been recognized as key players contributing to atherosclerotic plaque progression and destabilization. Particularly the role of innate immune cells is of major interest, following the recent paradigm shift that innate immunity, long considered to be incapable of learning, does exhibit immunological memory mediated via epigenetic reprogramming. Compelling evidence shows that atherosclerotic risk factors promote immune cell migration by pre-activation of circulating innate immune cells. Innate immune cell activation via metabolic and epigenetic reprogramming perpetuates a systemic low-grade inflammatory state in cardiovascular disease (CVD) that is also common in other chronic inflammatory disorders. This opens a new therapeutic area in which metabolic or epigenetic modulation of innate immune cells may result in decreased systemic chronic inflammation, alleviating CVD, and its co-morbidities.

Interactions between dyslipidemia and the immune system and their relevance as putative therapeutic targets in atherosclerosis

Cardiovascular disease (CVD) continues to be a leading cause of death worldwide with atherosclerosis being the major underlying pathology. The interplay between lipids and immune cells is believed to be a driving force in the chronic inflammation of the arterial wall during atherogenesis. Atherosclerosis is initiated as lipid particles accumulate and become trapped in vessel walls. The subsequent immune response, involving both adaptive and immune cells, progresses plaque development, which may be exacerbated under dyslipidemic conditions. Broad evidence, especially from animal models, clearly demonstrates the effect of lipids on immune cells from their development in the bone marrow to their phenotypic switching in circulation. Interestingly, recent research has also shown a long-lasting epigenetic signature from lipids on immune cells. Traditionally, cardiovascular therapies have approached atherosclerosis through lipid-lowering medications because, until recently, anti-inflammatory therapies have been largely unsuccessful in clinical trials. However, the recent Canakinumab Antiinflammatory Thrombosis Outcomes Study (CANTOS) provided pivotal support of the inflammatory hypothesis of atherosclerosis in man spurring on anti-inflammatory strategies to treat atherosclerosis. In this review, we describe the interactions between lipids and immune cells along with their specific outcomes as well as discuss their future perspective as potential cardiovascular targets.

The cardiac microenvironment uses non-canonical WNT signaling to activate monocytes after myocardial infarction

A disturbed inflammatory response following myocardial infarction (MI) is associated with poor prognosis and increased tissue damage. Monocytes are key players in healing after MI, but little is known about the role of the cardiac niche in monocyte activation. This study investigated microenvironment‐dependent changes in inflammatory monocytes after MI. RNA sequencing analysis of murine Ly6C^high monocytes on day 3 after MI revealed differential regulation depending on location. Notably, the local environment strongly impacted components of the WNT signaling cascade. Analysis of WNT modulators revealed a strong upregulation of WNT Inhibitory Factor 1 (WIF1) in cardiomyocytes—but not fibroblasts or endothelial cells—upon hypoxia. Compared to wild‐type (WT) littermates, WIF1 knockout mice showed severe adverse remodeling marked by increased scar size and reduced ejection fraction 4 weeks after MI. While FACS analysis on day 1 after MI revealed no differences in neutrophil numbers, the hearts of WIF1 knockouts contained significantly more inflammatory monocytes than hearts from WT animals. Next, we induced AAV‐mediated cardiomyocyte‐specific WIF1 overexpression, which attenuated the monocyte response and improved cardiac function after MI, as compared to control‐AAV‐treated animals. Finally, WIF1 overexpression in isolated cardiomyocytes limited the activation of non‐canonical WNT signaling and led to reduced IL‐1β and IL‐6 expression in monocytes/macrophages. Taken together, we investigated the cardiac microenvironment's interaction with recruited monocytes after MI and identified a novel mechanism of monocyte activation. The local initiation of non‐canonical WNT signaling shifts the accumulating myeloid cells toward a pro‐inflammatory state and impacts healing after myocardial infarction.

Traumatic Brain Injury Leads to Accelerated Atherosclerosis in Apolipoprotein E Deficient Mice

Traumatic brain injury (TBI) has been associated with atherosclerosis and cardiovascular mortality in humans. However the causal relationship between TBI and vascular disease is unclear. This study investigated the direct role of TBI on vascular disease using a murine model of atherosclerosis. Apolipoprotein E deficient mice were placed on a western diet beginning at 10 weeks of age. Induction of TBI or a sham operation was performed at 14 weeks of age and mice were sacrificed 6 weeks later at 20 weeks of age. MRI revealed evidence of uniform brain injury in all mice subjected to TBI. There were no differences in total cholesterol levels or blood pressure between the groups. Complete blood counts and flow cytometry analysis performed on peripheral blood 6 weeks following TBI revealed a higher percentage of Ly6C-high monocytes in mice subjected to TBI compared to sham-treated mice. Mice with TBI also showed elevated levels of plasma soluble E-selectin and bone marrow tyrosine hydroxylase. Analysis of atherosclerosis at the time of sacrifice revealed increased atherosclerosis with increased Ly6C/G immunostaining in TBI mice compared to sham-treated mice. In conclusion, progression of atherosclerosis is accelerated following TBI. Targeting inflammatory pathways in patients with TBI may reduce subsequent vascular complications.

Increased haematopoietic activity in patients with atherosclerosis

Aims

Experimental work posits that acute ischaemic events trigger haematopoietic activity, driving monocytosis, and atherogenesis. Considering the chronic low-grade inflammatory state in atherosclerosis, we hypothesized that haematopoietic hyperactivity is a persistent feature in cardiovascular disease (CVD). Therefore, we aimed to assess the activity of haematopoietic organs and haematopoietic stem and progenitor cells (HSPCs) in humans.

Methods and results

First, we performed 18F-fluorodeoxyglucose positron emission tomographic (18F-FDG PET) imaging in 26 patients with stable atherosclerotic CVD (ischaemic event >12 months ago), and 25 matched controls. In splenic tissue, 18F-FDG uptake was 2.68 ± 0.65 in CVD patients vs. 1.75 ± 0.54 in controls (1.6-fold higher; P< 0.001), and in bone marrow 3.20 ± 0.76 vs. 2.72 ± 0.46 (1.2-fold higher; P = 0.003), closely related to LDL cholesterol levels (LDLc, r = 0.72). Subsequently, we determined progenitor potential of HSPCs harvested from 18 patients with known atherosclerotic CVD and 30 matched controls; both groups were selected from a cohort of cancer patients undergoing autologous stem cell transplantation. In CVD patients, the normalized progenitor potential, expressed as the number of colony-forming units-granulocyte/monocyte (CFU-GM) colonies/CD34+ cell, was 1.6-fold higher compared with matched controls (P < 0.001). Finally, we assessed the effects of native and oxidized lipoproteins on HSPCs harvested from healthy donors in vitro. Haematopoietic stem and progenitor cells displayed a 1.5-fold increased CFU-GM capacity in co-culture with oxidized LDL in vitro (P = 0.002), which was inhibited by blocking oxidized phospholipids via E06 (P = 0.001).

Conclusion

Collectively, these findings strengthen the case for a chronically affected haematopoietic system, potentially driving the low-grade inflammatory state in patients with atherosclerosis.

Myocardial infarction does not affect circulating haematopoietic stem and progenitor cell self-renewal ability in a rat model

NEW FINDINGS

What is the central question of this study? Although peripheral blood haematopoietic stem and progenitor cells are potentially important in regeneration after acute myocardial infarction, their self-renewal ability in the post-acute phase has not yet been addressed. What is the main finding and its importance? In rat peripheral blood, we show that myocardial infarction does not negatively affect circulating haematopoietic stem and progenitor cell self-renewal ability 2 weeks after acute infarction, which suggests a constant regenerative potential in the myocardial infarction post-acute phase. Given the importance of peripheral blood haematopoietic stem and progenitor cells (HPCs) in post-acute regeneration after acute myocardial infarction (MI), the aim of the present study was to investigate the number and secondary replating capacity/self-renewal ability of HPCs in peripheral blood before and 2 weeks after MI. In female Lewis inbred rats (n = 9), MI was induced by ligation of the left coronary artery, and another nine underwent sham surgery, without ligation, for control purposes. Myocardial infarction was confirmed by troponin I concentrations 24 h after surgery. Peripheral blood was withdrawn and fractional shortening and ejection fraction of the left ventricle were assessed before (day 0) and 14 days after MI or sham surgery (day 14). After mononuclear cell isolation, primary and secondary functional colony-forming unit granulocyte-macrophage (CFU-GM) assays were performed in order to detect the kinetics of functional HPC colony counts and cell self-renewal ability in vitro. The CFU-GM counts and cell self-renewal ability remained unchanged (P > 0.05) in both groups at day 14, without interaction between groups. In the intervention group, higher day 0 CFU-GM counts showed a relationship to lower fractional shortening on day 14 (ρ = -0.82; P < 0.01). Myocardial infarction did not negatively affect circulating HPC self-renewal ability, which suggests a constant regenerative potential in the post-acute phase. A relationship of cardiac contractile function 14 days after MI with circulating CFU-GM counts on day 0 might imply functional colony count as a predictive factor for outcome after infarction.

Leukocyte diversity in resolving and nonresolving mechanisms of cardiac remodeling

In response to myocardial infarction (MI), time-dependent leukocyte infiltration is critical to program the acute inflammatory response. Post-MI leukocyte density, residence time in the infarcted area, and exit from the infarcted injury predict resolving or nonresolving inflammation. Overactive or unresolved inflammation is the primary determinant in heart failure pathology post-MI. Here, our review describes supporting evidence that the acute inflammatory response also guides the generation of healing and regenerative mediators after cardiac damage. Time-dependent leukocyte density and diversity and the magnitude of myocardial injury is responsible for the resolving and nonresolving pathway in myocardial healing. Post MI, the diversity of leukocytes, such as neutrophils, macrophages, and lymphocytes, has been explored that regulate the clearance of deceased cardiomyocytes by using the classic and reparative pathways. Among the innovative factors and intermediates that have been recognized as essential in acute the self-healing and clearance mechanism, we highlight specialized proresolving mediators as the emerging factor for post-MI reparative mechanisms-translational leukocyte modifiers, such as aging, the source of leukocytes, and the milieu around the leukocytes. In the clinical setting, it is possible that leukocyte diversity is more prominent as a result of risk factors, such as obesity, diabetes, and hypertension. Pharmacologic agents are critical modifiers of leukocyte diversity in healing mechanisms that may impair or stimulate the clearance mechanism. Future research is needed, with a focused approach to understand the molecular targets, cellular effectors, and receptors. A clear understanding of resolving and nonresolving inflammation in myocardial healing will help to develop novel targets with major emphasis on the resolution of inflammation in heart failure pathology.-Tourki, B., Halade, G. Leukocyte diversity in resolving and nonresolving mechanisms of cardiac remodeling.

Novel Biomarker MicroRNAs for Subtyping of Acute Coronary Syndrome: A Bioinformatics Approach

Acute coronary syndrome (ACS) is a life-threatening disease that affects more than half a million people in United States. We currently lack molecular biomarkers to distinguish the unstable angina (UA) and acute myocardial infarction (AMI), which are the two subtypes of ACS. MicroRNAs play significant roles in biological processes and serve as good candidates for biomarkers. In this work, we collected microRNA datasets from the Gene Expression Omnibus database and identified specific microRNAs in different subtypes and universal microRNAs in all subtypes based on our novel network-based bioinformatics approach. These microRNAs were studied for ACS association by pathway enrichment analysis of their target genes. AMI and UA were associated with 27 and 26 microRNAs, respectively, nine of them were detected for both AMI and UA, and five from each subtype had been reported previously. The remaining 22 and 21 microRNAs are novel microRNA biomarkers for AMI and UA, respectively. The findings are then supported by pathway enrichment analysis of the targets of these microRNAs. These novel microRNAs deserve further validation and will be helpful for personalized ACS diagnosis.

Metabolism Regulates Cellular Functions of Bone Marrow-Derived Cells used for Cardiac Therapy

Administration of bone marrow-derived mononuclear cells (BMC) may increase cardiac function after myocardial ischemia. However, the functional capacity of BMC derived from chronic heart failure (CHF) patients is significantly impaired. As modulation of the energy metabolism allows cells to match the divergent demands of the environment, we examined the regulation of energy metabolism in BMC from patients and healthy controls (HC). The glycolytic capacity of CHF-derived BMC is reduced compared to HC, whereas BMC of metabolically activated bone marrow after acute myocardial infarction reveal increased metabolism. The correlation of metabolic pathways with the functional activity of cells indicates an influence of metabolism on cell function. Reducing glycolysis without profoundly affecting ATP-production reversibly reduces invasion as well as colony forming capacity and abolishes proliferation of CD34(+) CD38(-) lin(-) hematopoietic stem and progenitor cells (HSPC). Ex vivo inhibition of glycolysis further reduced the pro-angiogenic activity of transplanted cells in a hind limb ischemia model in vivo. In contrast, inhibition of respiration, without affecting total ATP production, leads to a compensatory increase in glycolytic capacity correlating with increased colony forming capacity. Isolated CD34(+) , CXCR4(+) , and CD14(+) cells showed higher glycolytic activity compared to their negative counterparts. Metabolic activity was profoundly modulated by the composition of media used to store or culture BMC. This study provides first evidence that metabolic alterations influence the functional activity of human HSPC and BMC independent of ATP production. Changing the balance between respiration and glycolysis might be useful to improve patient-derived cells for clinical cardiac cell therapy. Stem Cells 2016;34:2236-2248.

Low-fidelity alternative DNA repair carcinogenesis theory may interpret many cancer features and anticancer strategies

We have proposed that the low-fidelity compensatory backup alternative DNA repair pathways drive multistep carcinogenesis. Here, we apply it to interpret the clinical features of cancer, such as mutator phenotype, tissue specificity, age specificity, diverse types of cancers originated from the same type of tissue, cancer susceptibility of patients with DNA repair-defective syndromes, development of cancer only for a selected number of individuals among those that share the same genetic defect, invasion and metastasis. Clinically, the theory predicts that to improve the efficacy of molecular targeted or synthetic lethal therapy, it may be crucial to inhibit the low-fidelity compensatory alternative DNA repair either directly or by blocking the signal transducers of the sustained microenvironmental stress.

Evaluation of the circulating CD34(+), CD309(+), and endothelial progenitor cells in patients with first attack of optic neuritis

BACKGROUND

Endothelial progenitor cells (EPCs) are present in circulation and contribute to vasculogenesis in adults. The aim of the present study was to determine the number of circulating EPCs in patients with optic neuritis (ON).

MATERIALS AND METHODS

Fifty patients with ON were diagnosed by expert neurologist and optometrist at the Feiz Hospital, Isfahan, Iran (2012-2013). Blood samples were collected from ON patients in the first attack. The number of EPCs was measured by flow cytometry through the assessment of CD34(+) and CD309(+) in patients and healthy individuals.

RESULTS

With using flow cytometry, CD34(+) and CD309(+) cells detected in peripheral blood cells of patients (n = 50) with ON, and healthy individuals (n = 30). Patients with ON had (mean = 66.71 ± 17.82) CD34(+) and CD309(+) cells compared with healthy controls (mean = 28.72 ± 22.46). In addition, there was no significant difference in CD309(+) cells in both groups.

CONCLUSION

This study showed elevated CD34(+) and CD309(+) cells in the early stage of the disease. Regarded to EPC increment in neural repair, it expected the EPC level be increased in these patients, but no detectable differences were observed among both markers in healthy and patient with first attack.

Innate immune cells in ischaemic heart disease: does myocardial infarction beget myocardial infarction?

Knowledge of macrophages in steady-state and diseased tissue is rapidly expanding, propelled by improved diagnostic capacity to detect and monitor cells in their native environments. In this review, we discuss implications for ischaemic heart disease and examine innate immune cell pathways that increase systemic leucocyte supply after myocardial infarction (MI). Acute MI alters the macrophage phenotype and supply chain from tissue resident to blood monocytes sourced from haematopoietic organs. That blood leucocytosis closely associates with cardiovascular mortality provides a strong motivation to understand why and how organ ischaemia alters cellular immunity.

Imaging systemic inflammatory networks in ischemic heart disease

While acute myocardial infarction mortality declines, patients continue to face reinfarction and/or heart failure. The immune system, which intimately interacts with healthy and diseased tissues through resident and recruited leukocytes, is a central interface for a global host response to ischemia. Pathways that enhance the systemic leukocyte supply may be potential therapeutic targets. Pre-clinically, imaging helps to identify immunity's decision nodes, which may serve as such targets. In translating the rapidly-expanding pre-clinical data on immune activity, the difficulty of obtaining multiple clinical tissue samples from involved organs is an obstacle that whole-body imaging can help overcome. In patients, molecular and cellular imaging can be integrated with blood-based diagnostics to assess the translatability of discoveries, including the activation of hematopoietic tissues after myocardial infarction, and serve as an endpoint in clinical trials. In this review, we discuss these concepts while focusing on imaging immune activity in organs involved in ischemic heart disease.

Migration towards SDF-1 selects angiogenin-expressing bone marrow monocytes endowed with cardiac reparative activity in patients with previous myocardial infarction

Introduction

Chemokine-directed migration is crucial for homing of regenerative cells to the infarcted heart and correlates with outcomes of cell therapy trials. Hence, transplantation of chemokine-responsive bone marrow cells may be ideal for treatment of myocardial ischemia. To verify the therapeutic activity of bone marrow mononuclear cells (BM-MNCs) selected by in vitro migration towards the chemokine stromal cell-derived factor-1 (SDF-1) in a mouse model of myocardial infarction (MI), we used BM-MNCs from patients with previous large MI recruited in the TransACT-1&2 cell therapy trials.

Methods

Unfractioned BM-MNCs, SDF-1-responsive, and SDF-1-nonresponsive BM-MNCs isolated by patients recruited in the TransACT-1&2 cell therapy trials were tested in Matrigel assay to evaluate angiogenic potential. Secretome and antigenic profile were characterized by flow cytometry. Angiogenin expression was measured by RT-PCR. Cells groups were also intramyocardially injected in an in vivo model of MI (8-week-old immune deficient CD1-FOXN1^nu/nu mice). Echocardiography and hemodynamic measurements were performed before and at 14 days post-MI. Arterioles and capillaries density, infiltration of inflammatory cells, interstitial fibrosis, and cardiomyocyte proliferation and apoptosis were assessed by immunohistochemistry.

Results

In vitro migration enriched for monocytes, while CD34⁺ and CD133⁺ cells and T lymphocytes remained mainly confined in the non-migrated fraction. Unfractioned total BM-MNCs promoted angiogenesis on Matrigel more efficiently than migrated or non-migrated cells. In mice with induced MI, intramyocardial injection of unfractionated or migrated BM-MNCs was more effective in preserving cardiac contractility and pressure indexes than vehicle or non-migrated BM-MNCs. Moreover, unfractioned BM-MNCs enhanced neovascularization, whereas the migrated fraction was unique in reducing the infarct size and interstitial fibrosis. In vitro studies on isolated cardiomyocytes suggest participation of angiogenin, a secreted ribonuclease that inhibits protein translation under stress conditions, in promotion of cardiomyocyte survival by migrated BM-MNCs.

Conclusions

Transplantation of bone marrow cells helps post-MI healing through distinct actions on vascular cells and cardiomyocytes. In addition, the SDF-1-responsive fraction is enriched with angiogenin-expressing monocytes, which may improve cardiac recovery through activation of cardiomyocyte response to stress. Identification of factors linking migratory and therapeutic outcomes could help refine regenerative approaches.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0028-y) contains supplementary material, which is available to authorized users.

Macrophages retain hematopoietic stem cells in the spleen via VCAM-1

Dutta et al. show that targeting VACM-1 expression in splenic macrophages impairs extramedullary hematopoiesis, thus reducing inflammation in mouse ischemic heart and atherosclerotic plaques.

Splenic myelopoiesis provides a steady flow of leukocytes to inflamed tissues, and leukocytosis correlates with cardiovascular mortality. Yet regulation of hematopoietic stem cell (HSC) activity in the spleen is incompletely understood. Here, we show that red pulp vascular cell adhesion molecule 1 (VCAM-1)⁺ macrophages are essential to extramedullary myelopoiesis because these macrophages use the adhesion molecule VCAM-1 to retain HSCs in the spleen. Nanoparticle-enabled in vivo RNAi silencing of the receptor for macrophage colony stimulation factor (M-CSFR) blocked splenic macrophage maturation, reduced splenic VCAM-1 expression and compromised splenic HSC retention. Both, depleting macrophages in CD169 iDTR mice or silencing VCAM-1 in macrophages released HSCs from the spleen. When we silenced either VCAM-1 or M-CSFR in mice with myocardial infarction or in ApoE^−/− mice with atherosclerosis, nanoparticle-enabled in vivo RNAi mitigated blood leukocytosis, limited inflammation in the ischemic heart, and reduced myeloid cell numbers in atherosclerotic plaques.

Immunosenescence in monocytes, macrophages, and dendritic cells: lessons learned from the lung and heart

In the absence of an immune challenge, healthy, aged individuals have a significantly higher basal inflammatory state where circulating levels of cytokines, including IL-6, TNF-α and IL-1β, are elevated [1]. This progressive pro-inflammatory state, termed "inflamm-aging", affects the phenotype/function of cells present in the aged as well as renders the older individuals more susceptible to a poor prognosis after systemic insults. Although it is important to understand the mechanisms that underlie the progression of disease, most preclinical analyses of disease therapies are performed in young adult mice that have an intact, functional immune system. Oftentimes, this is not necessarily representative of the immune disposition in the aged, let alone diseased, aged. Herein, two distinct responses that are not only commonly associated with aging but that also have dendritic cells and/or monocytes and macrophages as key players are discussed: pulmonary infection and myocardial infarction. Although studies of pulmonary infection in the aged have progressed significantly, studies of monocytes and macrophages in inflammation and cardiac injury following ischemia in the aged have not been as forthcoming. Nonetheless, several elegant studies have established the dynamic role of monocytes and macrophages post infarction. These will be discussed in light of what is known with aging.

Loss of Sirt3 limits bone marrow cell-mediated angiogenesis and cardiac repair in post-myocardial infarction

Sirtuin-3 (Sirt3) has a critical role in the regulation of human aging and reactive oxygen species (ROS) formation. A recent study has identified Sirt3 as an essential regulator of stem cell aging. This study investigated whether Sirt3 is necessary for bone marrow cell (BMC)-mediated cardiac repair in post-myocardial infarction (MI). In vitro, BMC-derived endothelial progenitor cells (EPCs) from wild type (WT) and Sirt3KO mice were cultured. EPC angiogenesis, ROS formation and apoptosis were assessed. In vivo, WT and Sirt3 KO mice were subjected to MI and BMCs from WT and Sirt3 KO mice were injected into ischemic area immediately. The expression of VEGF and VEGFR2 was reduced in Sirt3KO-EPCs. Angiogenic capacities and colony formation were significantly impaired in Sirt3KO-EPCs compared to WT-EPCs. Loss of Sirt3 further enhanced ROS formation and apoptosis in EPCs. Overexpression of Sirt3 or treatment with NADPH oxidase inhibitor apocynin (Apo, 200 and 400 microM) rescued these abnormalities. In post-MI mice, BMC treatment increased number of Sca1⁺/c-kit⁺ cells; enhanced VEGF expression and angiogenesis whereas Sirt3KO-BMC treatment had little effects. BMC treatment also attenuated NADPH oxidase subunits p47^phox and gp91^phox expression, and significantly reduced ROS formation, apoptosis, fibrosis and hypertrophy in post-MI mice. Sirt3KO-BMC treatment did not display these beneficial effects. In contrast, Sirt3KO mice treated with BMCs from WT mice attenuated myocardial apoptosis, fibrosis and improved cardiac function. Our data demonstrate that Sirt3 is essential for BMC therapy; and loss of Sirt3 limits BMC-mediated angiogenesis and cardiac repair in post-MI.

Detailed analysis of bone marrow from patients with ischemic heart disease and left ventricular dysfunction: BM CD34, CD11b, and clonogenic capacity as biomarkers for clinical outcomes

RATIONALE

Bone marrow (BM) cell therapy for ischemic heart disease (IHD) has shown mixed results. Before the full potency of BM cell therapy can be realized, it is essential to understand the BM niche after acute myocardial infarction (AMI).

OBJECTIVE

To study the BM composition in patients with IHD and severe left ventricular (LV) dysfunction.

METHODS AND RESULTS

BM from 280 patients with IHD and LV dysfunction were analyzed for cell subsets by flow cytometry and colony assays. BM CD34(+) cell percentage was decreased 7 days after AMI (mean of 1.9% versus 2.3%-2.7% in other cohorts; P<0.05). BM-derived endothelial colonies were significantly decreased (P<0.05). Increased BM CD11b(+) cells associated with worse LV ejection fraction (LVEF) after AMI (P<0.05). Increased BM CD34(+) percentage associated with greater improvement in LVEF (+9.9% versus +2.3%; P=0.03, for patients with AMI and +6.6% versus -0.02%; P=0.021 for patients with chronic IHD). In addition, decreased BM CD34(+) percentage in patients with chronic IHD correlated with decrement in LVEF (-2.9% versus +0.7%; P=0.0355).

CONCLUSIONS

In this study, we show a heterogeneous mixture of BM cell subsets, decreased endothelial colony capacity, a CD34+ cell nadir 7 days after AMI, a negative correlation between CD11b percentage and postinfarct LVEF, and positive correlation of CD34 percentage with change in LVEF after cell therapy. These results serve as a possible basis for the small clinical improvement seen in autologous BM cell therapy trials and support selection of potent cell subsets and reversal of comorbid BM impairment.

CLINICAL TRIAL REGISTRATIONS URL

http://www.clinicaltrials.gov. Unique identifiers: NCT00684021, NCT00684060, and NCT00824005.

Secretomes of apoptotic mononuclear cells ameliorate neurological damage in rats with focal ischemia

The pursuit of targeting multiple pathways in the ischemic cascade of cerebral stroke is a promising treatment option. We examined the regenerative potential of conditioned medium derived from rat and human apoptotic mononuclear cells (MNC), rMNC ^apo sec and hMNC ^apo sec, in experimental stroke.

We performed middle cerebral artery occlusion on Wistar rats and administered apoptotic MNC-secretomes intraperitoneally in two experimental settings. Ischemic lesion volumes were determined 48 hours after cerebral ischemia. Neurological evaluations were performed after 6, 24 and 48 hours. Immunoblots were conducted to analyze neuroprotective signal-transduction in human primary glia cells and neurons. Neuronal sprouting assays were performed and neurotrophic factors in both hMNC ^apo sec and rat plasma were quantified using ELISA.

Administration of rat as well as human apoptotic MNC-secretomes significantly reduced ischemic lesion volumes by 36% and 37%, respectively. Neurological examinations revealed improvement after stroke in both treatment groups. Co-incubation of human astrocytes, Schwann cells and neurons with hMNC ^apo sec resulted in activation of several signaling cascades associated with the regulation of cytoprotective gene products and enhanced neuronal sprouting in vitro. Analysis of neurotrophic factors in hMNC ^apo sec and rat plasma revealed high levels of brain derived neurotrophic factor (BDNF).

Our data indicate that apoptotic MNC-secretomes elicit neuroprotective effects on rats that have undergone ischemic stroke.

Involvement of monocytes/macrophages as key factors in the development and progression of cardiovascular diseases

Emerging evidence points to the involvement of specialized cells of the immune system as key drivers in the pathophysiology of cardiovascular diseases. Monocytes are an essential cell component of the innate immune system that rapidly mobilize from the bone marrow to wounded tissues where they differentiate into macrophages or dendritic cells and trigger an immune response. In the healthy heart a limited, but near-constant, number of resident macrophages have been detected; however, this number significantly increases during cardiac damage. Shortly after initial cardiac injury, e.g. myocardial infarction, a large number of macrophages harbouring a pro-inflammatory profile (M1) are rapidly recruited to the cardiac tissue, where they contribute to cardiac remodelling. After this initial period, resolution takes place in the wound, and the infiltrated macrophages display a predominant deactivation/pro-resolution profile (M2), promoting cardiac repair by mediating pro-fibrotic responses. In the present review we focus on the role of the immune cells, particularly in the monocyte/macrophage population, in the progression of the major cardiac pathologies myocardial infarction and atherosclerosis.

Cardiac macrophages and their role in ischaemic heart disease

Cardiac macrophages are abundant in the healthy heart and after myocardial infarction (MI). Different macrophage phenotypes likely promote myocardial health vs. disease. Infarct macrophages are inflammatory and derive from circulating monocytes produced by the haematopoietic system. These cells are centrally involved in inflammatory tissue remodelling, resolution of inflammation during post-MI healing, and left ventricular remodelling. Presumably, macrophages interact with myocytes, endothelial cells, and fibroblasts. Although macrophages are primarily recruited to the ischaemic myocardium, the remote non-ischaemic myocardium macrophage population changes dynamically after MI. Macrophages' known roles in defending the steady state and their pathological actions in other disease contexts provide a road map for exploring cardiac macrophages and their phenotypes, functions, and therapeutic potential. In our review, we summarize recent insights into the role of cardiac macrophages, focus on their actions after ischaemia, and highlight emerging research topics.

Metabolic activity of the spleen and bone marrow in patients with acute myocardial infarction evaluated by 18f-fluorodeoxyglucose positron emission tomograpic imaging

BACKGROUND

Atherosclerosis is considered to be an inflammatory disease associated with the activation of hematopoietic and immune-related organs such as the bone marrow (BM) and spleen. We evaluated the metabolic activity of those organs and of the carotid artery with (18)F-fluorodeoxyglucose positron emission tomography in patients with coronary artery disease, including acute myocardial infarction.

METHODS AND RESULTS

Whole-body combined (18)F-fluorodeoxyglucose positron emission tomography/computed tomography was performed in 32 patients with acute myocardial infarction, 33 patients with chronic stable angina, and 25 control subjects. The mean standard uptake value was calculated in the regions of interest in the spleen and the BM of lumbar vertebrae. The target-to-background ratio of the standard uptake values of the carotid artery and jugular vein was also calculated. In patients with acute myocardial infarction, the standard uptake values of the BM (1.67±0.16) and spleen (2.57±0.39), as well as the target-to-background ratio of the carotid artery (2.13±0.42), were significantly higher than the corresponding values of patients with angina (1.22±0.62; 2.03±0.35; 1.36±0.37; all P<0.001) and controls (0.80±0.44; 1.54±0.26; 1.22±0.22; all P<0.001), independent of traditional cardiovascular risk factors and high-sensitivity C-reactive protein. In all groups combined, the target-to-background ratio of the carotid artery was significantly associated with the standard uptake values of the BM (r=0.535; P<0.001), spleen (r=0.663; P<0.001), and high-sensitivity C-reactive protein (r=0.465; P<0.001).

CONCLUSIONS

The metabolic activity of the BM and spleen, as well as of the carotid artery, was highest in patients with acute myocardial infarction, intermediate in patients with angina, and lowest in control subjects. The activation of the BM and spleen was significantly associated with inflammatory activity of the carotid artery.

Postischemic revascularization: from cellular and molecular mechanisms to clinical applications

After the onset of ischemia, cardiac or skeletal muscle undergoes a continuum of molecular, cellular, and extracellular responses that determine the function and the remodeling of the ischemic tissue. Hypoxia-related pathways, immunoinflammatory balance, circulating or local vascular progenitor cells, as well as changes in hemodynamical forces within vascular wall trigger all the processes regulating vascular homeostasis, including vasculogenesis, angiogenesis, arteriogenesis, and collateral growth, which act in concert to establish a functional vascular network in ischemic zones. In patients with ischemic diseases, most of the cellular (mainly those involving bone marrow-derived cells and local stem/progenitor cells) and molecular mechanisms involved in the activation of vessel growth and vascular remodeling are markedly impaired by the deleterious microenvironment characterized by fibrosis, inflammation, hypoperfusion, and inhibition of endogenous angiogenic and regenerative programs. Furthermore, cardiovascular risk factors, including diabetes, hypercholesterolemia, hypertension, diabetes, and aging, constitute a deleterious macroenvironment that participates to the abrogation of postischemic revascularization and tissue regeneration observed in these patient populations. Thus stimulation of vessel growth and/or remodeling has emerged as a new therapeutic option in patients with ischemic diseases. Many strategies of therapeutic revascularization, based on the administration of growth factors or stem/progenitor cells from diverse sources, have been proposed and are currently tested in patients with peripheral arterial disease or cardiac diseases. This review provides an overview from our current knowledge regarding molecular and cellular mechanisms involved in postischemic revascularization, as well as advances in the clinical application of such strategies of therapeutic revascularization.

Myocardial injection of apelin-overexpressing bone marrow cells improves cardiac repair via upregulation of Sirt3 after myocardial infarction

Our previous study shows that treatment with apelin increases bone marrow cells (BMCs) recruitment and promotes cardiac repair after myocardial infarction (MI). The objective of this study was to investigate whether overexpression of apelin in BMCs improved cell therapy and accelerated cardiac repair and functional recovery in post-MI mice. Mouse myocardial infarction was achieved by coronary artery ligation and BMCs overexpressing apelin (apelin-BMCs) or GFP (GFP-BMCs) were injected into ischemic area immediately after surgery. In vitro, exposure of cultured BMCs to apelin led to a gradual increase in SDF-1á and CXCR4 expression. Intramyocardial delivery of apelin-BMCs in post-MI mice resulted in a significant increase number of APJ⁺/c-kit⁺/Sca1⁺ cells in the injected area compared to GFP-BMCs treated post-MI mice. Treatment with apelin-BMCs increased expression of VEGF, Ang-1 and Tie-2 in post-MI mice. Apelin-BMCs treatment also significantly increased angiogenesis and attenuated cardiac fibrosis formation in post-MI mice. Most importantly, treatment with apelin-BMCs significantly improved left ventricular (LV) systolic function in post-MI mice. Mechanistically, Apelin-BMCs treatment led to a significant increase in Sirtuin3 (Sirt3) expression and reduction of reactive oxygen species (ROS) formation. Treatment of cultured BMCs with apelin also increased Notch3 expression and Akt phosphorylation. Apelin treatment further attenuated stress-induced apoptosis whereas knockout of Sirt3 abolished anti-apoptotic effect of apelin in cultured BMCs. Moreover, knockout of Sirt3 significantly attenuated apelin-BMCs-induced VEGF expression and angiogenesis in post-MI mice. Knockout of Sirt3 further blunted apelin-BMCs-mediated improvement of cardiac repair and systolic functional recovery in post-MI mice. These data suggest that apelin improves BMCs therapy on cardiac repair and systolic function in post-MI mice. Upregulation of Sirt3 may contribute to the protective effect of apelin-BMCs therapy.

Monocyte and macrophage heterogeneity in the heart

Monocytes and macrophages are innate immune cells that reside and accumulate in the healthy and injured heart. The cells and their subsets pursue distinct functions in steady-state and disease, and their tenure may range between hours and months. Some subsets are highly inflammatory, whereas others support tissue repair. This review discusses current concepts of lineage relationships and crosstalk of systems, highlights open questions, and describes tools for studying monocyte and macrophage subsets in the murine and human heart.

Age-associated changes in the ecological niche: implications for mesenchymal stem cell aging

Adult stem cells are critical for organ-specific regeneration and self-renewal with advancing age. The prospect of being able to reverse tissue-specific post-injury sequelae by harvesting, culturing and transplanting a patient's own stem and progenitor cells is exciting. Mesenchymal stem cells have emerged as a reliable stem cell source for this treatment modality and are currently being tested in numerous ongoing clinical trials. Unfortunately, the fervor over mesenchymal stem cells is mitigated by several lines of evidence suggesting that their efficacy is limited by natural aging. This article discusses the mechanisms and manifestations of age-associated deficiencies in mesenchymal stem cell efficacy. A consideration of recent experimental findings suggests that the ecological niche might be responsible for mesenchymal stem cell aging.

Why cancer cells metastasize?

Metastasis is so complicated and well organized that there should be a good reason for it to happen. Here a hypothesis is proposed that metastasis of cancer cells is an abnormal form of migration of native stem/progenitor cells since cancer cells derive from stem/progenitor cells and may inherit stemness, including migration ability. This is an intrinsic potential and external cause mode. During metastasis, cancer cells are involved in the stem/progenitor cell recruitment to meet the need of organism for homeostasis, regeneration and repair, mediated by external signals and using inherent mechanisms but leading to catastrophic results. The "seed and soil" hypothesis can be redefined as that the "soil" is formed under certain circumstances and the "seed" is attracted to its particular "soil". Cancer cells in the microenviroment mimicking stem cell niche may have superiority in reactivity to metastatic signals. And very few of migrating cancer cells can form metastases. The conditions suitable for metastasis formation are still waiting to be revealed. The hypothesis tries to explain why cancer cells metastasize. It is hoped that the examination of this hypothesis may lead us to the real answer.

Leukocyte behavior in atherosclerosis, myocardial infarction, and heart failure

Cardiovascular diseases claim more lives worldwide than any other. Etiologically, the dominant trajectory involves atherosclerosis, a chronic inflammatory process of lipid-rich lesion growth in the vascular wall that can cause life-threatening myocardial infarction (MI). Those who survive MI can develop congestive heart failure, a chronic condition of inadequate pump activity that is frequently fatal. Leukocytes (white blood cells) are important participants at the various stages of cardiovascular disease progression and complication. This Review will discuss leukocyte function in atherosclerosis, MI, and heart failure.

Imaging macrophage development and fate in atherosclerosis and myocardial infarction

Macrophages are central regulators of disease progression in both atherosclerosis and myocardial infarction (MI). In atherosclerosis, macrophages are the dominant leukocyte population that influences lesional development. In MI, which is caused by atherosclerosis, macrophages accumulate readily and have important roles in inflammation and healing. Molecular imaging has grown considerably as a field and can reveal biological process at the molecular, cellular and tissue levels. Here, we explore how various imaging modalities, from intravital microscopy in mice to organ-level imaging in patients, are contributing to our understanding of macrophages and their progenitors in cardiovascular disease.

Stem cell compartmentalization in diabetes and high cardiovascular risk reveals the role of DPP-4 in diabetic stem cell mobilopathy

Bone marrow (BM) derived stem and progenitor cells contribute to cardiovascular homeostasis and are affected by cardiovascular risk factors. We devised a clinical data-driven approach to test candidate stem cell mobilizing mechanisms in pre-clinical models. We found that PB and BM CD34+ cell counts were directly correlated, and that most circulating CD34+ cells were viable, non-proliferating and derived from the BM. Thus, we analyzed PB and BM CD34+ cell levels as a two-compartment model in 72 patients with or without cardiovascular disease. Self-organizing maps showed that disturbed compartmentalization of CD34+ cells was associated with aging and cardiovascular risk factors especially diabetes. High activity of DPP-4, a regulator of the mobilizing chemokine SDF-1α, was associated with altered stem cell compartmentalization. For validation of these findings, we assessed the role of DPP-4 in the BM mobilization response of diabetic rats. Diabetes differentially affected DPP-4 activity in PB and BM and impaired stem/progenitor cell mobilization after ischemia or G-CSF administration. DPP-4 activity in the BM was required for the mobilizing effect of G-CSF, while in PB it blunted ischemia-induced mobilization. Indeed, DPP-4 deficiency restored ischemia (but not G-CSF)-induced stem cell mobilization and improved vascular recovery in diabetic animals. In conclusion, the analysis of stem cell compartmentalization in humans led us to discover mechanisms of BM unresponsiveness in diabetes determined by tissue-specific DPP-4 dysregulation.

Advances in stem cell mobilization

The use of mobilized peripheral blood stem cells (PBSCs) has largely replaced the use of bone marrow as a source of stem cells for both allogeneic and autologous stem cell transplantation. G-CSF with or without chemotherapy is the most commonly used regimen for stem cell mobilization. Some donors or patients, especially the heavily pretreated patients, fail to mobilize the targeted number of stem cells with this regimen. A better understanding of the mechanisms involved in hematopoietic stem cell (HSC) trafficking could lead to the development of newer mobilizing agents and therapeutic approaches. This review will cover the current methods for stem cell mobilization and recent developments in the understanding of the biology of stem cells and the bone marrow microenvironment.