Jennifer K. Lang

Complementary patterns of gene expression by human oligodendrocyte progenitors and their environment predict determinants of progenitor maintenance and differentiation

Glial progenitor cells are abundant in adult human white matter. This study was designed to identify signaling pathways regulating their self‐renewal and fate.

Statin treatment of adult human glial progenitors induces PPARγ-mediated oligodendrocytic differentiation

The statins have been proposed as possible therapeutic agents for a variety of autoimmune disorders, including multiple sclerosis. In a genomic screen, we found that glial progenitor cells (GPCs) of the adult human white matter expressed significant levels of the principal statin target, HMG‐CoA reductase, as well as additional downstream members of the sterol synthesis pathway. We therefore asked if statin treatment might influence the differentiated fate of adult glial progenitor cells. To assess the functional importance of the sterol synthesis pathway to adult human glial progenitors, we used simvastatin or pravastatin to inhibit HMG‐CoA reductase, and then assessed the phenotypic differentiation of the progenitors, as well as the molecular concomitants thereof. We found that both statins induced a dose‐dependent induction of oligodendrocyte phenotype, and concomitant reduction in progenitor number. Oligodendrocyte commitment was associated with induction of the sterol‐regulated nuclear co‐receptor PPARγ, and could be blocked by the specific PPARγ antagonist GW9662. Thus, statins may promote oligodendrocyte lineage commitment by parenchymal glial progenitor cells; this might reduce the available progenitor pool, and hence degrade the long‐term regenerative competence of the adult white matter.

Inhibiting Extracellular Vesicle Release from Human Cardiosphere Derived Cells with Lentiviral Knockdown of nSMase2 Differentially Effects Proliferation and Apoptosis in Cardiomyocytes, Fibroblasts and Endothelial Cells In Vitro

Numerous studies have shown a beneficial effect of cardiosphere-derived cell (CDC) therapy on regeneration of injured myocardium. Paracrine signaling by CDC secreted exosomes may contribute to improved cardiac function. However, it has not yet been demonstrated by a genetic approach that exosome release contributes to the therapeutic effect of transplanted CDCs. By employing a lentiviral knockdown (KD) strategy against neutral spingomyelinase 2 (nSMase2), a crucial gene in exosome secretion, we have defined the role of physiologically secreted human CDC-derived exosomes on cardiac fibroblast, endothelial cell and primary cardiomyocyte proliferation, cell death, migration and angiogenesis using a series of in vitro coculture assays. We found that secretion of hCDC-derived exosomes was effectively inhibited by nSMase2 lentiviral KD and shRNAi expression was stable and constitutive. hCDC exosome release contributed to the angiogenic and pro-migratory effects of hCDCs on HUVECs, decreased proliferation of fibroblasts, and decreased apoptosis of cardiomyocytes. These in vitro reactions support a role for exosome secretion as a paracrine mechanism of stem cell-mediated cardiac repair in vivo. Importantly, we have established a novel tool to test constitutive inhibition of exosome secretion in stem cell populations in animal models of cardiac disease.

Statins enhance clonal growth of late outgrowth endothelial progenitors and increase myocardial capillary density in the chronically ischemic heart.

Background Coronary artery disease and ischemic heart disease are leading causes of heart failure and death. Reduced blood flow to heart tissue leads to decreased heart function and symptoms of heart failure. Therapies to improve heart function in chronic coronary artery disease are important to identify. HMG-CoA reductase inhibitors (statins) are an important therapy for prevention of coronary artery disease, but also have non-cholesterol lowering effects. Our prior work showed that pravastatin improves contractile function in the chronically ischemic heart in pigs. Endothelial progenitor cells are a potential source of new blood vessels in ischemic tissues. While statins are known to increase the number of early outgrowth endothelial progenitor cells, their effects on late outgrowth endothelial progenitor cells (LOEPCs) and capillary density in ischemic heart tissue are not known. We hypothesized that statins exert positive effects on the mobilization and growth of late outgrowth EPCs, and capillary density in ischemic heart tissue. Methodology/Principal Findings We determined the effects of statins on the mobilization and growth of late outgrowth endothelial progenitor cells from pigs. We also determined the density of capillaries in myocardial tissue in pigs with chronic myocardial ischemia with or without treatment with pravastatin. Pravastatin therapy resulted in greater than two-fold increase in CD31+ LOEPCs versus untreated animals. Addition of pravastatin or simvastatin to blood mononuclear cells increased the number of LOEPCs greater than three fold in culture. Finally, in animals with chronic myocardial ischemia, pravastatin increased capillary density 46%. Conclusions Statins promote the derivation, mobilization, and clonal growth of LOEPCs. Pravastatin therapy in vivo increases myocardial capillary density in chronically ischemic myocardium, providing an in vivo correlate for the effects of statins on LOEPC growth in vitro. Our findings provide evidence that statin therapy can increase the density of capillaries in the chronically ischemic heart.

LDL cholesterol modulates human CD34+ HSPCs through effects on proliferation and the IL-17 G-CSF axis.

Background Hypercholesterolemia plays a critical role in atherosclerosis. CD34+ CD45dim Lineage- hematopoietic stem/progenitor cells (HSPCs) give rise to the inflammatory cells linked to atherosclerosis. In mice, high cholesterol levels mobilize HSPCs into the bloodstream, and promote their differentiation to granulocytes and monocytes. The objective of our study was to determine how cholesterol levels affect HSPC quantity in humans. Methods We performed a blinded, randomized hypothesis generating study in human subjects (n=12) treated sequentially with statins of differing potencies to vary lipid levels. CD34+ HSPC levels in blood were measured by flow cytometry. Hematopoietic colony forming assays confirmed the CD34+ population studied as HSPCs with multlineage differentiation potential. Mobilizing cytokine levels were measured by ELISA. Results The quantity of HSPCs was 0.15 ± 0.1% of buffy coat leukocytes. We found a weak, positive correlation between CD34+ HSPCs and both total and LDL cholesterol levels (r2=0.096, p < 0.025). Additionally, we tested whether cholesterol modulates CD34+ HSPCs through direct effects or on the levels of mobilizing cytokines. LDL cholesterol increased cell surface expression of CXCR4, G-CSFR affecting HSPC migration, and CD47 mediating protection from phagocytosis by immune cells. LDL cholesterol also increased proliferation of CD34+ HSPCs (28 ± 5.7%, n=6, p < 0.03). Finally, the HSPC mobilizing cytokine G-CSF (r2=0.0683, p < 0.05), and its upstream regulator IL-17 (r2=0.0891, p < 0.05) both correlated positively with LDL cholesterol, while SDF-1 levels were not significantly affected. Conclusions Our findings support a model where LDL cholesterol levels positively correlate with CD34+ HSPC levels in humans through effects on the levels of G-CSF via IL-17 promoting mobilization of HSPCs, and by direct effects of LDL cholesterol on HSPC proliferation. The findings are provocative of further study to determine if HSPCs, like cholesterol levels, are linked to CVD events.

Cholesterol affects retinal nerve fiber layer thickness in patients with multiple sclerosis with optic neuritis.

To evaluate the associations between retinal nerve fiber layer (RNFL) thickness and lipid profiles in multiple sclerosis (MS).

Cholesterol and Hematopoietic Stem Cells: Inflammatory Mediators of Atherosclerosis

Atherosclerosis causing heart attack and stroke is the leading cause of death in the modern world. Therapy for end‐stage atherosclerotic disease using CD34+ hematopoietic cells has shown promise in human clinical trials, and the in vivo function of hematopoietic and progenitor cells in atherogenesis is becoming apparent. Inflammation plays a central role in the pathogenesis of atherosclerosis. Cholesterol is a modifiable risk factor in atherosclerosis, but in many patients cholesterol levels are only mildly elevated. Those with high cholesterol levels often have elevated circulating monocyte and neutrophil counts. How cholesterol affects inflammatory cell levels was not well understood. Recent findings have provided new insight into the interaction among hematopoietic stem cells, cholesterol, and atherosclerosis. In mice, high cholesterol levels or inactivation of cholesterol efflux transporters have multiple effects on hematopoietic stem cells (HSPCs), including promoting their mobilization into the bloodstream, increasing proliferation, and differentiating HSPCs to the inflammatory monocytes and neutrophils that participate in atherosclerosis. Increased levels of interleukin‐23 (IL‐23) stimulate IL‐17 production, resulting in granulocyte colony‐stimulating factor (G‐CSF) secretion, which subsequently leads to HSPC release into the bloodstream. Collectively, these findings clearly link elevated cholesterol levels to increased circulating HSPC levels and differentiation to inflammatory cells that participate in atherosclerosis. Seminal questions remain to be answered to understand how cholesterol affects HSPC‐mobilizing cytokines and the role they play in atherosclerosis. Translation of findings in animal models to human subjects may include HSPCs as new targets for therapy to prevent or regress atherosclerosis in patients

Sox10-MCS5 enhancer dynamically tracks human oligodendrocyte progenitor fate

In this study, we sought to establish a novel method to prospectively and dynamically identify live human oligodendrocyte precursor cells (OPCs) and oligodendrocyte lineage cells from brain dissociates and pluripotent stem cell culture. We selected a highly conserved enhancer element of the Sox10 gene, known as MCS5, which directs reporter expression to oligodendrocyte lineage cells in mouse and zebrafish. We demonstrate that lentiviral Sox10-MCS5 induced expression of GFP at high levels in a subpopulation of human CD140a/PDGFαR-sorted OPCs as well as their immature oligodendrocyte progeny. Furthermore, we show that almost all Sox10-MCS5:GFP(high) cells expressed OPC antigen CD140a and human OPCs expressing SOX10, OLIG2, and PDGFRA mRNAs could be prospectively identified using GFP based fluorescence activated cells sorting alone. Additionally, we established a human induced pluripotent cell (iPSC) line transduced with the Sox10-MCS5:GFP reporter using a Rex-Neo cassette. Similar to human primary cells, GFP expression was restricted to embryoid bodies containing both oligodendrocyte progenitor and oligodendrocyte cells and co-localized with NG2 and O4-positive cells respectively. As such, we have developed a novel reporter system that can track oligodendrocyte commitment in human cells, establishing a valuable tool to improve our understanding and efficiency of human oligodendrocyte derivation.

Progenitor cell-based myelination as a model for cell-based therapy of the central nervous system.

Diseases of the brain and spinal cord are especially daunting challenges for cell-based strategies of repair, given the multiplicity of cell types within the adult central nervous system, and the precision with which they must interact in both space and time. Nonetheless, a number of diseases are especially appropriate for cell-based therapy, in particular those in which single phenotypes are lost. Foremost among these are the disorders of myelin, in which oligodendrocytes are the specific and often sole victims of the underlying disease process. These include not only the vascular, traumatic, and inflammatory demyelinations of adulthood, but also the congenital and childhood dysmyelinating syndromes of the pediatric leukodystrophies. These congenital disorders of myelin formation and maintenance may present especially compelling targets for cell-based neurological therapy.

Therapeutic Potential of Engineered Extracellular Vesicles

Extracellular vesicles (EVs) comprise a heterogeneous group of small membrane vesicles, including exosomes, which play a critical role in intracellular communication and regulation of numerous physiological processes in health and disease. Naturally released from virtually all cells, these vesicles contain an array of nucleic acids, lipids and proteins which they transfer to target cells within their local milieu and systemically. They have been proposed as a means of “cell-free, cell therapy” for cancer, immune disorders, and more recently cardiovascular disease. In addition, their unique properties of stability, biocompatibility, and low immunogenicity have prompted research into their potential as therapeutic delivery agents for drugs and small molecules. In this review, we aim to provide a comprehensive overview of the current understanding of extracellular vesicle biology as well as engineering strategies in play to improve their therapeutic potential.