An investigation into murine pericyte shape change in response to inflammatory stimuli in vitro and in vivo
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Leukocyte transmigration through venular walls into the surrounding tissue is a crucial event during inflammatory responses. Despite increased understanding of the mechanisms associated with leukocyte migration through endothelial cells, little is known about the mechanisms mediating the subsequent migration through the pericyte layer and the basement membrane. We previously reported that gaps between adjacent pericytes are co-localised with matrix protein low expression regions in the basement membrane, regions that are preferentially used by leukocytes to penetrate venular walls (Wang et al., 2006; Voisin et al., 2009; Voisin et al., 2010). This study extended these findings to other vascular beds showing that pericyte morphology is heterogeneous in different tissues (Voisin et al., 2010). To investigate whether pericytes facilitate the transmigration process through direct morphological changes at sites of inflammation, neutrophil transmigration and pericyte shape change was analysed in whole mounted TNF-α- and IL-1β-stimulated murine cremaster muscles by immunofluorescence labelling and confocal microscopy. Post-capillary pericytes exhibited shape change resulting in a significant increase in mean gap size between adjacent cells. Time-course studies indicated that TNF-α-induced shape change preceded neutrophil transmigration. This response was PMN-independent as it was also noted in PMN depleted mice. Parallel studies investigated the effect of these cytokines on shape change of murine pericyte-like C3H/10T1/2 cells in vitro by time lapse microscopy. C3H/10T1/2 cells also exhibited significant shape change in response to direct TNF-α- and IL-1β-stimulation in vitro. Post-capillary venular pericytes in vivo and C3H/10T1/2 cells in vitro expressed the respective cytokine receptors, TNFRI, TNFRII and IL-1RI, indicating that pericytes can respond directly to pro-inflammatory cytokines. Finally, pericyte involvement in neutrophil transmigration in vivo was investigated in real time by confocal intra vital microscopy using α-SMA-RFPcherryxLys-EGFP mice. Neutrophils preferentially used enlarged gaps to migrate into the surrounding tissue.
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