Wnt-ligands are among key morphogens that mediate patterning of the anterior territories of the developing brain in mammals. We qualified the role of Wnt-signals in regional specification and subregional organization of the human telencephalon using human pluripotent stem cells (hPSCs). One step neural conversion of hPSCs using SMAD inhibitors leads to progenitors with a default rostral identity. It provides an ideal biological substrate for investigating the role of Wnt signaling in both anteroposterior and dorso-ventral processes. Challenging hPSCneural derivatives with Wnt-antagonists, alone or combined with sonic hedgehog (Shh), we found that Wntinhibition promote both telencephalic specification and ventral patterning of telencephalic neural precursors in a dose-dependent manner. Using optimal Wnt-antagonist and Shh-agonist signals we produced human ventraltelencephalic precursors, committed to differentiation into striatal projection neurons both in vitro and in vivo after homotypic transplantation in quinolinate-lesioned rats. This study indicates that sequentially organized Wntsignals play a key role in the development of human ventral telencephalic territories from which the striatum arise. In addition, the optimized production of hPSCderived striatal cells described here offers a relevant biological resource for exploring and curing Huntington disease.

The conversion of prion protein (PrPC) to its protease-resistant isoform is involved in the pathogenesis of prion diseases. Although PrPC is highly expressed in neurons and other cell types, its physiological function still remains elusive. Here, we describe how we evaluated its expression, subcellular localization and putative function in brain endothelial cells, which constitute the blood-brain barrier. We detected its expression in microvascular endothelium in mouse brain sections and at intercellular junctions of freshly isolated brain microvessels and cultured brain endothelial cells of mouse, rat and human origin. PrPC co-localized with the adhesion molecule platelet endothelial cell adhesion molecule-1 (PECAM-1); moreover, both PrPC and PECAM-1 were present in raft membrane microdomains. Using mixed cultures of wild-type and PrPC-deficient mouse brain endothelial cells, we observed that PrPC accumulation at cell-cell contacts was probably dependent on homophilic interactions between adjacent cells. Moreover, we report that anti-PrPC antibodies unexpectedly inhibited transmigration of U937 human monocytic cells as well as freshly isolated monocytes through human brain endothelial cells. Significant inhibition was observed with various anti-PrPC antibodies or blocking anti-PECAM-1 antibodies as control. Our results strongly support the conclusion that PrPC is expressed by brain endothelium as a junctional protein that is involved in the trans-endothelial migration of monocytes.

Decreased expression of neuronal genes such as brainderived neurotrophic factor (BDNF) is associated with several neurological disorders. One molecular mechanism associated with Huntington disease (HD) is a discrete increase in the nuclear activity of the transcriptional repressor REST/NRSF binding to repressor element-1 (RE1) sequences. High-throughput screening of a library of 6,984 compounds with luciferase-assay measuring REST activity in neural derivatives of human embryonic stem cells led to identify two benzoimidazole-5-carboxamide derivatives that inhibited REST silencing in a RE1-dependent manner. The most potent compound, X5050, targeted REST degradation, but neither REST expression, RNA splicing nor binding to RE1 sequence. Differential transcriptomic analysis revealed the upregulation of neuronal genes targeted by REST in wild-type neural cells treated with X5050. This activity was confirmed in neural cells produced from human induced pluripotent stem cells derived from a HD patient. Acute intraventricular delivery of X5050 increased the expressions of BDNF and several other REST-regulated genes in the prefrontal cortex of mice with quinolinate-induced striatal lesions. This study demonstrates that the use of pluripotent stem cell derivatives can represent a crucial step toward the identification of pharmacological compounds with therapeutic potential in neurological affections involving decreased expression of neuronal genes associated to increased REST activity, such as Huntington disease. STEM CELLS

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