Targeting Lysophosphatidic Acid Signaling Retards Culture-Associated Senescence of Human Marrow Stromal Cells

Marrow stromal cells (MSCs) isolated from mesenchymal tissues can propagate in vitro to some extent and differentiate into various tissue lineages to be used for cell-based therapies. Cellular senescence, which occurs readily in continual MSC culture, leads to loss of these characteristic properties, representing one of the major limitations to achieving the potential of MSCs. In this study, we investigated the effect of lysophosphatidic acid (LPA), a ubiquitous metabolite in membrane phospholipid synthesis, on the senescence program of human MSCs. We show that MSCs preferentially express the LPA receptor subtype 1, and an abrogation of the receptor engagement with the antagonistic compound Ki16425 attenuates senescence induction in continually propagated human MSCs. This anti-aging effect of Ki16425 results in extended rounds of cellular proliferation, increased clonogenic potential, and retained plasticity for osteogenic and adipogenic differentiation. Expressions of p16Ink4a, Rb, p53, and p21Cip1, which have been associated with cellular senescence, were all reduced in human MSCs by the pharmacological inhibition of LPA signaling. Disruption of this signaling pathway was accompanied by morphological changes such as cell thinning and elongation as well as actin filament deformation through decreased phosphorylation of focal adhesion kinase. Prevention of LPA receptor engagement also promoted ubiquitination-mediated c-Myc elimination in MSCs, and consequently the entry into a quiescent state, G0 phase, of the cell cycle. Collectively, these results highlight the potential of pharmacological intervention against LPA signaling for blunting senescence-associated loss of function characteristic of human MSCs

OX40 ligand newly expressed on bronchiolar progenitors mediates influenza infection and further exacerbates pneumonia

Influenza virus epidemics potentially cause pneumonia, which is responsible for much of the mortality due to the excessive immune responses. The role of costimulatory OX40-OX40 ligand (OX40L) interactions has been explored in the non-infectious pathology of influenza pneumonia. Here, we describe a critical contribution of OX40L to infectious pathology, with OX40L deficiency, but not OX40 deficiency, resulting in decreased susceptibility to influenza viral infection. Upon infection, bronchiolar progenitors increase in number for repairing the influenza-damaged epithelia. The OX40L expression is induced on the progenitors for the antiviral immunity during the infectious process. However, these defense-like host responses lead to more extensive infection owing to the induced OX40L with -2,6 sialic acid modification, which augments the interaction with the viral hemagglutinin. In fact, the specific antibody against the sialylated site of OX40L exhibited therapeutic potency in mitigating the OX40L-mediated susceptibility to influenza. Our data illustrate that the influenza-induced expression of OX40L on bronchiolar progenitors has pathogenic value to develop a novel therapeutic approach against influenza

LPA_1/3 inhibition of human MSCs reduced actin polymerization and increased cell-cycle quiescence.

<p><b>A, B.</b> Phenotypic characteristics of human MSCs treated with Ki16425 or vehicle alone for 48 h after plating. Shown are phase-contrast images (panel <b>A</b>) and fluorescent images in which filamentous actin (F-actin) was visualized with green phalloidin-FITC staining and nuclei were stained with red propidium iodide (panel <b>B</b>). Scale bars, 200 µm. <b>C.</b> Western blotting analysis to evaluate the phosphorylation and activation status of focal adhesion kinase (FAK). <b>D.</b> Cell-cycle analysis. Human MSCs treated with Ki16425 or vehicle alone for 72 h were fixed and then stained for DNA and RNA with 7-AAD and pyronin Y, respectively. Their cell-cycle status was assessed based on their DNA and RNA content by flow cytometry. A representative of three experiments is shown on the left side, and the bar graph summarizes the results of the G₀ proportion on the right side. The data are presented as the means ± standard error (<i>n</i> = 3). <b>E.</b> Western blotting analysis of signaling molecules associated with the Akt pathway. For panels <b>C</b> and <b>E</b>, human MSCs were cultured in the presence or absence of Ki16425 for the indicated times prior to cell lysis.</p

Decreased self-renewal capacity associated with senescence was prevented in human MSCs following treatment with Ki16425, an LPA₁/LPA₃ antagonist.

<p><b>A.</b> Growth kinetics during serial passage. Human MSCs at passage 2 (8.1 population doublings) were serially passaged every 9 days in the presence or absence of Ki16425. Cumulative population doublings are presented as the means of duplicates. <b>B.</b> Western blotting analysis of total and phosphorylated cPLA2 in human MSCs at passage 2. <b>C.</b> Real-time PCR analysis of LPA receptor gene expression in human MSCs at passage 2. Levels of mRNA were quantified relative to the mean of LPA₁ samples. <b>D.</b> CFU-F assay. Human MSCs at passage 2 were cultured in the presence or absence of Ki16425 for two additional passages (27 days). CFU-F colonies initiated from the treated cells (passage 5, 100 cells) were counted after 15 days of normal culture. On the right side are shown representative CFU-F colonies stained with crystal violet. <b>E.</b> SA-β-Gal assay. The total SA-β-Gal activities of Ki16425- and vehicle-treated human MSCs were quantified in the wells of six-well plates as the luminescent intensity (relative luminescence units, RLU). On the right side are shown representative human MSCs stained for SA-β-Gal. Scale bars in inset boxes, 200 µm. <b>F.</b> Telomere measurement. Telomere lengths were determined in Ki16425- and vehicle-treated human MSCs by real-time PCR and quantified relative to the mean of vehicle controls. <b>G.</b> Western blotting analysis of cell-cycle components. Human MSCs at passage 2 were cultured in the presence or absence of Ki16425 for the indicated days prior to cell lysis. Fold-change represents decrease in band intensity of Ki16425 treatment for 18 days compared with a control treatment for the same period of time. For panels <b>C</b>, <b>D</b>, <b>E</b>, and <b>F</b>, the data are presented as the means ± standard error (<i>n</i> = 3).</p