Oligodendrocyte Precursor Cells Support Blood-Brain Barrier Integrity via TGF-β Signaling

Trophic coupling between cerebral endothelium and their neighboring cells is required for the development and maintenance of blood-brain barrier (BBB) function. Here we report that oligodendrocyte precursor cells (OPCs) secrete soluble factor TGF-β1 to support BBB integrity. Firstly, we prepared conditioned media from OPC cultures and added them to cerebral endothelial cultures. Our pharmacological experiments showed that OPC-conditioned media increased expressions of tight-junction proteins and decreased in vitro BBB permeability by activating TGB-β-receptor-MEK/ERK signaling pathway. Secondly, our immuno-electron microscopic observation revealed that in neonatal mouse brains, OPCs attach to cerebral endothelial cells via basal lamina. And finally, we developed a novel transgenic mouse line that TGF-β1 is knocked down specifically in OPCs. Neonates of these OPC-specific TGF-β1 deficient mice (OPC-specific TGF-β1 partial KO mice: PdgfraCre/Tgfb1flox/wt mice or OPC-specific TGF-β1 total KO mice: PdgfraCre/Tgfb1flox/flox mice) exhibited cerebral hemorrhage and loss of BBB function. Taken together, our current study demonstrates that OPCs increase BBB tightness by upregulating tight junction proteins via TGF-β signaling. Although astrocytes and pericytes are well-known regulators of BBB maturation and maintenance, these findings indicate that OPCs also play a pivotal role in promoting BBB integrity

Reactive astrocytes promote adhesive interactions between brain endothelium and endothelial progenitor cells via HMGB1 and beta-2 integrin signaling

Endothelial progenitor cells (EPCs) may contribute to neurovascular repair after stroke and neurodegeneration. A key step in this process should involve adhesive interactions between EPCs and the targeted cerebral endothelium. Here, we tested the hypothesis that reactive astrocytes may play a critical role in enhancing adhesive interactions and transmigration of EPCs across cerebral endothelial cells. Transiently seeding EPCs onto a monolayer of RBE.4 rat brain endothelial cells resulted in a time-dependent adherence between the two cell types. Blocking β2 integrins on EPCs or blocking the receptor for advanced glycation endproducts (RAGE) on endothelial cells significantly decreased EPC-endothelial adherence. Next, we tested whether reactive astrocytes can enhance this process by growing EPCs, brain endothelial cells and astrocytes together in a transwell co-culture system. The presence of reactive astrocytes in the lower chamber significantly promoted adherence between EPCs and endothelial cells in the upper chamber. This process involved the release of soluble HMGB1 from reactive astrocytes that then upregulated endothelial expression of RAGE via Egr1 signaling. Directly adding HMGB1 to the transwell system also promoted EPC-endothelial adhesion and accelerated EPC transmigration into the lower chamber. These initial findings provide proof-of-concept that reactive astrocytes promote crosstalk between cerebral endothelium and EPCs. Further investigation of this phenomenon may lead to a better understanding of cell–cell interactions required for neurovascular recovery after stroke

Farmer adoptability for livelihood transformations in the Mekong Delta: a case in Ben Tre province

Sustainable livelihood development is an ongoing challenge worldwide, and has regained importance due to threats of water shortages and climate change. To cope with changing climatic, demographic and market conditions in Vietnam’s Mekong Delta (VMD) an agricultural transformation process has been suggested in the recent Mekong Delta Plan. This agricultural transformation process requires the implementation of alternative livelihood models. The majority of current agricultural livelihood models in the VMD have been introduced by the government in a top-down manner. In this study, we applied a bottom-up approach to understand the motivations and abilities of local farmers to adopt alternative livelihood models. It is based on the MOTA methodological framework, which is further tested with the use of multivariate analyses. The study was conducted in Ben Tre coastal province. Results showed that farmers’ motivations and abilities to apply alternative models vary substantially among different groups, driven by their perceptions on triggers and opportunities. Acknowledging this diversity is essential to the development of agricultural transformation plans. Furthermore, based on the analysis, a projection of the precise support that communities need to supplement their knowledge, skills and financial capacities, as well as interventions to reduce the risks of new livelihood models, is given

OPC-derived TGF-β1 and BBB integrity in vivo.

<p><b>A.</b> The OPC-specific TGF-β1 partial or total KO mice showed hemorrhage at post-natal day 0–1. <b>B–C.</b> IgG staining showed that in the OPC-specific TGF-β1 partial or total KO mice, IgG was leaked from blood vessels into brain parenchyma. Green: IgG, Orange: Lectin (endothelial marker), scale bar = 100 µm. Mean + SD of n = 4–5, *p<0.05 vs control group. <b>D.</b> The OPC-specific TGF-β1 deficient mice exhibited BBB leakages (IgG staining) and aberrant ZO-1 structures.</p

OPC-derived TGF-β1 and BBB integrity in vitro.

<p><b>A.</b> We prepared conditioned media from OPCs (OPC-CM), and then added them to cerebral endothelial RBE.4 cells. <b>B.</b> OPC-CM increased in vitro BBB tightness (i.e. decreased permeability of endothelial monolayer), and the TGF-β-receptor signaling inhibitor SB431542 (10 µM) cancelled the effects of OPC-CM. Mean ± SD of n = 3. *p<0.05 vs control (OPC-CM: −, SB431542: −), #P<0.05 vs OPC-CM only (OPC-CM: +, SB431542: −). <b>C–D.</b> Correspondingly, OPC-CM increased the expressions of tight junction proteins, and once again, SB431542 (10 µM) cancelled the effects of OPC-CM. <b>E.</b> Immunostaining confirmed that our cultured rat OPCs produced TGF-β1. PDGF-R-α staining was used to confirm the purity of our OPC cultures. <b>F.</b> LDH assay showed that the TGF-β receptor inhibitor SB431542 (10 µM) did not affect endothelial viability. Mean ± SD of n = 3.</p

OPC-endothelium interaction.

<p><b>A.</b> Immunostaining showed that some OPCs (green: PDGF-R-α) are located closely to cerebral endothelium (red: CD31) in mice at post-natal day 0–1. Scale bar = 50 µm. <b>B.</b> Triple staining showed that there is little overlap between PDGF-R-α and PDGF-R-β. Scale bar = 10 µm. <b>C.</b> Electron micrography also confirmed that OPCs attached directly to the basal lamina (Bl) of endothelial cells in corpus callosum. arrows: PDGF-R-α positive signals, Scale bar = 1 µm.</p

Proposed model for OPC-BBB interaction.

<p>Trophic coupling between OPCs and cerebral endothelium may play an important role in the BBB function. TGF-β1 may mediate the cell-cell interaction; i.e. OPCs secrete TGF-β1, which then binds to its receptor, followed by activating MEK/ERK pathway to increase the BBB tightness.</p

TGF-β1 expression in vascular-related brain cells.

<p>Immunostaining confirmed no clear differences in TGF-β1 expression in (<b>A</b>) cerebral endothelium assessed by CD31 staining, (<b>B</b>) astrocytes assessed by GFAP staining, and (<b>C</b>) pericytes assessed by PDGF-R-β staining at post-natal day 0 in the OPC-specific TGF-β1 deficient mice (OPC-specific TGF-β1 partial KO mice: <i>Pdgfra^Cre</i>/<i>Tgfb1^flox/wt</i> mice or OPC-specific TGF-β1 total KO mice: <i>Pdgfra^Cre</i>/<i>Tgfb1^flox/flox</i> mice).</p