Single-Cell Transcriptomics of Human Mesenchymal Stem Cells Reveal Age-Related Cellular Subpopulation Depletion and Impaired Regenerative Function.

Although bone marrow-derived mesenchymal stem cells (BM-MSCs) are widely recognized as promising therapeutic agents, the age-related impacts on cellular function remain largely uncharacterized. In this study, we found that BM-MSCs from young donors healed wounds in a xenograft model faster compared with their aged counterparts (p < .001). Given this significant healing advantage, we then used single-cell transcriptomic analysis to provide potential molecular insights into these observations. We found that the young cells contained a higher proportion of cells characterized by a higher expression of genes involved in tissue regeneration. In addition, we identified a unique, quiescent subpopulation that was exclusively present in young donor cells. Together, these findings may explain a novel mechanism for the enhanced healing capacity of young stem cells and may have implications for autologous cell therapy in the extremes of age. Stem Cells 2019;37:240-246.

Alveolar macrophages are critical for the inhibition of allergic asthma by mesenchymal stromal cells.

Multipotent mesenchymal stromal cells (MSCs) possess reparative and immunoregulatory properties, making them attractive candidates for cellular therapy. However, the majority of MSCs administered i.v. encounter a pulmonary impasse and soon disappear from the lungs, raising the question of how they induce such durable immunosuppressive effects. Using a mouse model of allergic asthma, we show that administration of MSCs isolated from human bone marrow, umbilical cord, or adipose tissue provoked a pronounced increase in alveolar macrophages and inhibited hallmark features of asthma, including airway hyperresponsiveness, eosinophilic accumulation, and Th2 cytokine production. Importantly, selective depletion of this macrophage compartment reversed the therapeutic benefit of MSC treatment on airway hyperresponsiveness. Our data demonstrate that human MSCs exert cross-species immunosuppressive activity, which is mediated by alveolar macrophages in allergic asthma. As alveolar macrophages are the predominant immune effector cells at the air-tissue interface in the lungs, this study provides a compelling mechanism for durable MSC effects in the absence of sustained engraftment.

Therapeutic Breast Reconstruction Using Gene Therapy-Delivered IFNγ Immunotherapy.

After mastectomy, breast reconstruction is increasingly performed using autologous tissue with the aim of improving quality of life. During this procedure, autologous tissue is excised, relocated, and reattached using microvascular anastomoses at the site of the extirpated breast. The period during which the tissue is ex vivo may allow genetic modification without any systemic exposure to the vector. Could such access permit delivery of therapeutic agents using the tissue flap as a vehicle? Such delivery may be more targeted and oncologically efficient than systemic therapy, and avoid systemic complications. The cytokine IFNγ has antitumor effects, and systemic toxicity could be circumvented by localized delivery of the IFNγ gene via gene therapy to autologous tissue used for breast reconstruction, which then releases IFNγ and exerts antitumor effects. In a rat model of loco-regional recurrence (LRR) with MADB-106-Luc and MAD-MB-231-Luc breast cancer cells, autologous tissue was transduced ex vivo with an adeno-associated viral vector encoding IFNγ. The "Therapeutic Reconstruction" released IFNγ at the LRR site and eliminated cancer cells, significantly decreased tumor burden, and increased survival compared with sham reconstruction (P <0.05). Mechanistically, localized IFNγ immunotherapy stimulated M1 macrophages to target cancer cells within the regional confines of the modified tumor environment. This concept of "Therapeutic Breast Reconstruction" using ex vivo gene therapy of autologous tissue offers a new application for immunotherapy in breast cancer with a dual therapeutic effect of both reconstructing the ablative defect and delivering local adjuvant immunotherapy.

Enhanced hematopoietic stem cell function mediates immune regeneration following sex steroid blockade.

Mechanisms underlying age-related defects within lymphoid-lineages remain poorly understood. We previously reported that sex steroid ablation (SSA) induced lymphoid rejuvenation and enhanced recovery from hematopoietic stem cell (HSC) transplantation (HSCT). We herein show that, mechanistically, SSA induces hematopoietic and lymphoid recovery by functionally enhancing both HSC self-renewal and propensity for lymphoid differentiation through intrinsic molecular changes. Our transcriptome analysis revealed further hematopoietic support through rejuvenation of the bone marrow (BM) microenvironment, with upregulation of key hematopoietic factors and master regulatory factors associated with aging such as Foxo1. These studies provide important cellular and molecular insights into understanding how SSA-induced regeneration of the hematopoietic compartment can underpin recovery of the immune system following damaging cytoablative treatments. These findings support a short-term strategy for clinical use of SSA to enhance the production of lymphoid cells and HSC engraftment, leading to improved outcomes in adult patients undergoing HSCT and immune depletion in general.

Selective endothelial overexpression of arginase II induces endothelial dysfunction and hypertension and enhances atherosclerosis in mice.

BACKGROUND: Cardiovascular disorders associated with endothelial dysfunction, such as atherosclerosis, have decreased nitric oxide (NO) bioavailability. Arginase in the vasculature can compete with eNOS for L-arginine and has been implicated in atherosclerosis. The aim of this study was to evaluate the effect of endothelial-specific elevation of arginase II expression on endothelial function and the development of atherosclerosis. METHODOLOGY/PRINCIPAL FINDINGS: Transgenic mice on a C57BL/6 background with endothelial-specific overexpression of human arginase II (hArgII) gene under the control of the Tie2 promoter were produced. The hArgII mice had elevated tissue arginase activity except in liver and in resident peritoneal macrophages, confirming endothelial specificity of the transgene. Using small-vessel myography, aorta from these mice exhibited endothelial dysfunction when compared to their non-transgenic littermate controls. The blood pressure of the hArgII mice was 17% higher than their littermate controls and, when crossed with apoE -/- mice, hArgII mice had increased aortic atherosclerotic lesions. CONCLUSION: We conclude that overexpression of arginase II in the endothelium is detrimental to the cardiovascular system.

Arginase II knockout mouse displays a hypertensive phenotype despite a decreased vasoconstrictory profile.

Arginase upregulation is associated with aging and cardiovascular diseases. In this study we report on the cardiovascular phenotype of the arginase II knockout (KO) mouse. We demonstrate that vascular sensitivity and reactivity altered over time in these animals such that no influence on responses to vasoconstrictor activity was observed in 7-week-old KO mice, but dampened responses to norepinephrine and phenylephrine were observed by 10 and 15 weeks with Rho kinase influencing these effects in the 15-week-old animals. Despite these dampened vasoconstrictory responses, KO mice demonstrated increased mean arterial pressure from 8 weeks old. This hypertensive phenotype was associated with an increase in left ventricular weight, left ventricular systolic pressure, and diminished diastolic function. KO mice also show enhanced plasma norepinephrine turnover, suggesting an increased sympathetic outflow. In conclusion, our data suggest that global loss of arginase II activity results in hypertension. We suggest that this strain of mouse warrants further investigation as a potentially novel model of hypertension.