Yupu Deng

Mesenchymal stem cells reduce inflammation while enhancing bacterial clearance and improving survival in sepsis.

RATIONALE Sepsis refers to the clinical syndrome of severe systemic inflammation precipitated by infection. Despite appropriate antimicrobial therapy, sepsis-related morbidity and mortality remain intractable problems in critically ill patients. Moreover, there is no specific treatment strategy for the syndrome of sepsis-induced multiple organ dysfunction. OBJECTIVES We hypothesized that mesenchymal stem cells (MSCs), which have been shown to have immunomodulatory properties, would reduce sepsis-induced inflammation and improve survival in a polymicrobial model of sepsis. METHODS Sepsis was induced in C57Bl/6J mice by cecal ligation and puncture (CLP), followed 6 hours later by an intravenous injection of MSCs or saline. Twenty-eight hours after CLP, plasma, bronchoalveolar lavage fluid and tissues were collected for analyses. Longer-term studies were performed with antibiotic coadministration to assess the effect of MSCs on survival. MEASUREMENTS AND MAIN RESULTS MSC treatment significantly reduced mortality in septic mice receiving appropriate antimicrobial therapy. MSCs alone reduced systemic and pulmonary cytokine levels in mice with CLP-induced sepsis, preventing acute lung injury and organ dysfunction, despite the low levels of cell persistence. Microarray data highlighted an overall down-regulation of inflammation and inflammation-related genes (such as IL-10, IL-6) and a shift toward up-regulation of genes involved in promoting phagocytosis and bacterial killing. Finally, bacterial clearance was significantly greater in MSC-treated mice, in part due to enhanced phagocytotic activity of the host immune cells. CONCLUSIONS These data demonstrate that MSCs have beneficial effects on experimental sepsis, possibly by paracrine mechanisms, and suggest that immunomodulatory cell therapy may be an effective adjunctive treatment to reduce sepsis-related morbidity and mortality.

Mice expressing BMPR2R899X transgene in smooth muscle develop pulmonary vascular lesions

Familial pulmonary arterial hypertension (PAH) is associated with mutations in bone morphogenetic protein type II receptor (BMPR2). Many of these mutations occur in the BMPR2 tail domain, leaving the SMAD functions intact. To determine the in vivo consequences of BMPR2 tail domain mutation, we created a smooth muscle-specific doxycycline-inducible BMPR2 mutation with an arginine to termination mutation at amino acid 899. When these SM22-rtTA x TetO(7)-BMPR2(R899X) mice had transgene induced for 9 wk, starting at 4 wk of age, they universally developed pulmonary vascular pruning as assessed by fluorescent microangiography. Approximately one-third of the time, the induced animals developed elevated right ventricular systolic pressures (RVSP), associated with extensive pruning, muscularization of small pulmonary vessels, and development of large structural pulmonary vascular changes. These lesions included large numbers of macrophages and T cells in their adventitial compartment as well as CD133-positive cells in the lumen. Small vessels filled with CD45-positive and sometimes CD3-positive cells were a common feature in all SM22-rtTA x TetO(7)-BMPR2(R899X) mice. Gene array experiments show changes in stress response, muscle organization and function, proliferation, and apoptosis and developmental pathways before RVSP increases. Our results show that the primary phenotypic result of BMPR2 tail domain mutation in smooth muscle is pulmonary vascular pruning leading to elevated RVSP, associated with early dysregulation in multiple pathways with clear relevance to PAH. This model should be useful to the research community in examining early molecular and physical events in the development of PAH and as a platform to validate potential treatments.

Innate Immunity in the Therapeutic Actions of Endothelial Progenitor Cells in Pulmonary Hypertension

Direct injection of endothelial progenitor cells (EPCs) into the circulation has shown therapeutic benefit in both experimental models and clinical studies of pulmonary arterial hypertension (PAH). Using the monocrotaline (MCT)-induced rat model of PAH, we investigated the role of innate immunity in the therapeutic activity of two types of putative EPCs derived from human peripheral blood mononuclear cells: an early population of endothelial-like, culture-modified monocytes (E-CMMs) and late-outgrowth EPCs (L-EPCs), which exhibit a strong endothelial phenotype. In the athymic nude rat, E-CMMs prevented MCT-induced increases in right ventricular systolic pressure (P < 0.001) and right ventricular hypertrophy (P < 0.01) when administered 3 days after MCT challenge, whereas L-EPCs were ineffective. However, in both cases, there was a lack of cell persistence within the lungs at 24 hours after injection, likely due to residual natural killer (NK) cell activity in the model. Although ablation of NK and NK-T cells with anti-asialo-GM-1 antiserum enhanced the retention of both E-CMMs and L-EPCs, still no benefit was seen with L-EPCs, and the efficacy of E-CMMs was lost. In vitro characterization revealed that E-CMMs resemble a regulatory subtype of dendritic cells, producing IL-10, but not IL-12, in response to inflammatory stimuli. Coculture studies demonstrated the capacity of E-EPCs to stimulate autologous human and nude rat NK cells in vitro. These data support a novel mode of action for human E-CMMs in the prevention of PAH, whereby they act through an immune-dependent mechanism, potentially involving the stimulation of NK cells.

Marked Strain-Specific Differences in the SU5416 Rat Model of Severe Pulmonary Arterial Hypertension

We assessed the pulmonary hemodynamic response to vascular endothelial growth factor receptor, type 2, inhibition using SU5416 (SU) with and without chronic hypoxia (CH) in different background strains and colonies of rats. A single subcutaneous injection of SU (20 mg/kg) or vehicle was administered to different substrains of Sprague-Dawley (SD) rats, and they were compared with Lewis and Fischer rats, with and without exposure to CH (10% O2 for 3 wk). Remarkably, a unique colony of SD rats from Charles River Laboratories, termed the SD-hyperresponsive type, exhibited severe pulmonary arterial hypertension (PAH) with SU alone, characterized by increased right ventricular systolic pressure, right ventricular/left ventricular plus septal weight ratio, and arteriolar occlusive lesions at 7-8 weeks (all P < 0.0001 versus vehicle). In contrast, the other SD substrain from Harlan Laboratories, termed SD-typical type, as well as Fischer rats, developed severe PAH only when exposed to SU and CH, whereas Lewis rats showed only a minimal response. All SD-typical type rats survived for up to 13 weeks after SU/CH, whereas SD-hyperresponsive type rats exhibited mortality after SU and SU/CH (35% and 50%, respectively) at 8 weeks. Fischer rats exposed to SU/CH exhibited the greatest mortality at 8 weeks (78%), beginning as early as 4 weeks after SU and preceded by right ventricle enlargement. Of note, a partial recovery of PAH after 8 weeks was observed in the SD-typical type substrain only. In conclusion, variation in strain, even between colonies of the same strain, has a remarkable influence on the nature and severity of the response to SU, consistent with an important role for genetic modifiers of the PAH phenotype.

The enzymatic degradation of hyaluronan is associated with disease progression in experimental pulmonary hypertension

Hyaluronan (HA) degradation fragments have been linked to inflammation in a wide range of lung diseases. In idiopathic pulmonary arterial hypertension, HA accumulation has been associated with advanced disease. In this study, we investigated the potential role of HA degradation in the early stages of disease by examining HA distribution, molecular mass, synthesis, and enzymatic degradation at different stages of disease progression in a rat model of monocrotaline (MCT)-induced pulmonary hypertension (PH). At 28 days post-MCT, severe PH was associated with increased total lung HA (P = 0.04). In contrast, a significant decrease in total lung HA was observed on day 10, before the onset of PH (P = 0.02). Molecular mass analysis revealed a loss of high molecular mass (HMM) HA at 10 and 24 days post-MCT, followed by an increase in HMM HA at 28 days. Expression of HA synthase 2 (HAS2) was elevated in MCT-challenged animals at 24 and 28 days, consistent with increased synthesis of HMM HA. Analysis by Morgan Elson assay and zymography demonstrated increased hyaluronidase-1 activity in the lungs of MCT-challenged rats, indicating that the observed increases in HAS2 expression and HA synthesis were counterbalanced, in part, by enhanced degradation. The present data demonstrate that, in the MCT model, early-stage PH is associated with enhanced hyaluronidase-1 activity, while both degradation and synthesis are increased at later stages. Thus an early increase in the generation of proinflammatory HA fragments may play a role in the onset and progression of pulmonary arterial hypertension.

Discordant Regulation of microRNA Between Multiple Experimental Models and Human Pulmonary Hypertension

BACKGROUND The dysregulation of microRNA (miRNA) is known to contribute to the pathobiology of pulmonary arterial hypertension (PAH). However, the relationships between changes in tissue and circulating miRNA levels associated with different animal models and human pulmonary hypertension (PH) have not been defined. METHODS A set of miRNAs that have been causally implicated in PH, including miR-17, -21, -130b, -145, -204, -424, and -503, were measured by reverse transcription-quantitative polymerase chain reaction in the plasma, lung, and right ventricle of three of the most common rodent models of PH: the rat monocrotaline and SU5416 plus chronic hypoxia (SuHx) models and the mouse chronic hypoxia model. Plasma miRNA levels were also evaluated in a cohort of patients with PAH and healthy subjects. RESULTS Several miRNA showed PH model-dependent perturbations in plasma and tissue levels; however, none of these were conserved across all three experimental models. Principle component analysis of miR expression changes in plasma revealed distinct clustering between rodent models, and SuHx-triggered PH showed the greatest similarity to human PAH. Changes in the plasma levels of several miRNA also correlated with changes in tissue expression. In particular, miR-424 was concordantly increased (1.3- to 1.5-fold, P < .05) in the plasma, lung, and right ventricle of hypoxic mice and in the plasma of patients with PAH. CONCLUSIONS miRNAs with established etiologic roles in PH showed context-dependent changes in tissue and circulating levels, which were not consistent across rodent models and human PAH. This suggests different miRNA-dependent mechanisms may contribute to experimental and clinical PH, complicating potential diagnostic and therapeutic applications amenable to these miRNAs.

Occlusive Lung Arterial Lesions in Endothelial-Targeted, Fas-Induced Apoptosis Transgenic Mice

Pulmonary arterial hypertension (PAH) is a lethal disease that is characterized by functional and structural abnormalities involving distal pulmonary arterioles that result in increased pulmonary vascular resistance and ultimately right heart failure. In experimental models of pulmonary hypertension, endothelial cell (EC) apoptosis is a necessary trigger for the development of obliterative lung arteriopathy, inducing the emergence of hyperproliferative and apoptosis-resistant vascular cells. However, it has not been established whether EC apoptosis is sufficient for the induction of complex lung arteriolar lesions. We generated a conditional transgenic system in mice to test the hypothesis that lung endothelial cell apoptosis is sufficient to induce a PAH phenotype. The Fas-induced apoptosis (FIA) construct was expressed under the control of endothelial-specific Tie2 promoter (i.e., EFIA mice), and administration of a small molecule dimerizing agent, AP20187, resulted in modest pulmonary hypertension, which was associated with obliterative vascular lesions localized to distal lung arterioles in a proportion of transgenic mice. These lesions were characterized by proliferating cells, predominantly CD68 macrophages. Although endothelial cell apoptosis was also seen in the kidney, evidence of subsequent arteriopathy was seen only in the lung. This model provides direct evidence that lung endothelial cell apoptosis acts as a trigger to initiate a PAH phenotype and provides initial insight into the potential mechanisms that underlie a lung-specific arterial response to endothelial injury.

Cardiotrophin 1 stimulates beneficial myogenic and vascular remodeling of the heart

The post-natal heart adapts to stress and overload through hypertrophic growth, a process that may be pathologic or beneficial (physiologic hypertrophy). Physiologic hypertrophy improves cardiac performance in both healthy and diseased individuals, yet the mechanisms that propagate this favorable adaptation remain poorly defined. We identify the cytokine cardiotrophin 1 (CT1) as a factor capable of recapitulating the key features of physiologic growth of the heart including transient and reversible hypertrophy of the myocardium, and stimulation of cardiomyocyte-derived angiogenic signals leading to increased vascularity. The capacity of CT1 to induce physiologic hypertrophy originates from a CK2-mediated restraining of caspase activation, preventing the transition to unrestrained pathologic growth. Exogenous CT1 protein delivery attenuated pathology and restored contractile function in a severe model of right heart failure, suggesting a novel treatment option for this intractable cardiac disease.

Lack of elevation in plasma levels of pro-inflammatory cytokines in common rodent models of pulmonary arterial hypertension: questions of construct validity for human patients

Translational research depends on the relevance of animal models and how well they replicate human disease. Here, we investigated plasma levels of three important pro-inflammatory cytokines (TNFα, IL-6, and MCP-1), known to be elevated in human pulmonary arterial hypertension (PAH), and systematically assessed their levels in PAH patients compared to five different rodent models of pulmonary hypertension (PH). A consistent immunoassay platform (Luminex xMAP) and source (Millipore) was used to measure all specimens. PAH patients (n = 29) exhibited significant elevations in all three cytokines (median [IQR] pg/mL; TNFα, 7.0 [4.8–11.7]; IL-6, 9.2 [3.8–17.2]; MCP-1, 109 [65–142]) versus healthy participants (n = 20) (median [IQR] pg/mL; TNFα, 3.0 [2.0–3.6]; IL-6, 1.7 [0.5–7.2]; MCP-1, 79 [49–93]. In contrast, mice with PH established after three weeks of hypoxia (n = 18) or SU5416 plus hypoxia (n = 20) showed no significant change in their plasma cytokine levels versus controls (n = 16), based on three to four independent experiments per group. Similarly, plasma cytokine levels were not elevated in rats with PH established three weeks after monocrotaline (n = 23), eight weeks after SU5416 alone (n = 10) or six to eight weeks after SU5416 plus hypoxia (n = 21) versus controls (n = 36 rats), based on three to eight independent experiments per group. Positive biologic control specimens from sepsis patients (n = 9), cecal-ligation and puncture (CLP)-induced septic mice (n = 6), and lipopolysaccharide-induced septic rats (n = 4) showed robust elevations in all three cytokines. This study suggests that animal models commonly used for the development of novel diagnostic and therapeutic approaches for PAH may have limited construct validity with respect to markers of systemic immune activation seen in human patients.

A Lymphocyte-Dependent Mode of Action for Imatinib Mesylate in Experimental Pulmonary Hypertension

The capacity of imatinib mesylate to reverse established pulmonary arterial hypertension (PAH) has been attributed to a reduction in pulmonary arterial muscularization via inhibition of platelet-derived growth factor receptor-β on vascular smooth muscle cells. However, there is also a significant immunomodulatory component to the action of imatinib that may account for its efficacy in PAH. We found that monocrotaline-induced pulmonary hypertension was associated with a significant decrease in pulmonary natural killer (NK) cells and T lymphocytes and the accumulation of macrophages in the lungs of F344 rats. The prevention of pulmonary hypertension by imatinib blocked these changes in pulmonary leukocyte content and induced elevations in pulmonary interferon-γ, tumor necrosis factor α, and IL-10, corresponding to the enhanced activity of splenic NK cells ex vivo. Treatment with anti-asialo GM1 antiserum (ASGM1), which ablated circulating NK cells and depleted T cells, eliminated the therapeutic benefit of imatinib. ASGM1-treated animals also exhibited significant pulmonary arteriolar muscularization in response to monocrotaline challenge compared with immunocompetent controls despite daily imatinib administration to both groups. In the athymic rat, imatinib decreased right ventricular hypertrophy and pulmonary arteriolar muscularization in monocrotaline-challenged animals versus saline-treated controls but did not prevent pulmonary macrophage accumulation or the development of pulmonary hypertension. These data demonstrate that the immunomodulatory effects of imatinib are critical to its therapeutic action in experimental PAH.