Structural and functional studies of TBC1D23 C-terminal domain provide a link between endosomal trafficking and PCH.

Pontocerebellar hypoplasia (PCH) is a group of neurological disorders that affect the development of the brain, in particular, the pons and cerebellum. Homozygous mutations of TBC1D23 have been found recently to lead to PCH; however, the underlying molecular mechanisms remain unclear. Here, we show that the crystal structure of the TBC1D23 C-terminal domain adopts a Pleckstrin homology domain fold and selectively binds to phosphoinositides, in particular, PtdIns(4)P, through one surface while binding FAM21 via the opposite surface. Mutation of key residues of TBC1D23 or FAM21 selectively disrupts the endosomal vesicular trafficking toward the Trans-Golgi Network. Finally, using the zebrafish model, we show that PCH patient-derived mutants, impacting either phosphoinositide binding or FAM21 binding, lead to abnormal neuronal growth and brain development. Taken together, our data provide a molecular basis for the interaction between TBC1D23 and FAM21, and suggest a plausible role for PtdIns(4)P in the TBC1D23-mediating endosome-to-TGN trafficking pathway. Defects in this trafficking pathway are, at least partially, responsible for the pathogenesis of certain types of PCH.

[Association of Elevated Platelet Microparticles with Disease Activity in Rheumatoid Arthritis].

OBJECTIVES: To explore the expression of platelets microparticles (PMPs) in peripheral blood (PB) and synovial fluid (SF) of rheumatoid arthritis (RA) patients and its correlation with clinical inflammatory parameters. METHODS: The levels of PMPs in PB were detected by flow cytometry in 26 active RA patients and 15 healthy control (HC). SF was collected from 16 patients. The percentages of CD62P+PMPs, CD154+PMPs and clinical parameters (including CRP, ESR, RF and ACPA) were also measured, then the correlations of PMPs with these parameters were analyzed. RESULTS: PMPs levels in PB of RA patients were higher than those in PB from HC and those in SF of RA patients (P< 0.01). CD62P+PMPs levels in PB of RA patients were higher than those in PB of HC and those in SF of RA patients (P< 0.05). CD154+PMPs levels in PB of RA patients were higher than those in PB of HC (P< 0.01) and those in SF of RA patients (P< 0.05). The levels of PB PMPs were positively correlated with disease activity score DAS28 ( r=0.462, P=0.018), but not with ESR, CRP, RF or ACPA. The levels of SF PMPs were not correlated with any of them (P>0.05). CONCLUSIONS: PMPs may be involved in immune regulation and systemic inflammation of RA. The elevated levels of PMPs could be a potential biomarker for RA.

Targeting Th17 Cells with Small Molecules and Small Interference RNA.

T helper 17 (Th17) cells play a central role in inflammatory and autoimmune diseases via the production of proinflammatory cytokines interleukin- (IL-) 17, IL-17F, and IL-22. Anti-IL-17 monoclonal antibodies show potent efficacy in psoriasis but poor effect in rheumatoid arthritis (RA) and Crohn's disease. Alternative agents targeting Th17 cells may be a better way to inhibit the development and function of Th17 cells than antibodies of blocking a single effector cytokine. Retinoic acid-related orphan receptor gamma t (RORγt) which acts as the master transcription factor of Th17 differentiation has been an attractive pharmacologic target for the treatment of Th17-mediated autoimmune disease. Recent progress in technology of chemical screen and engineering nucleic acid enable two new classes of therapeutics targeting RORγt. Chemical screen technology identified several small molecule specific inhibitors of RORγt from a small molecule library. Systematic evolution of ligands by exponential enrichment (SELEX) technology enabled target specific aptamers to be isolated from a random sequence oligonucleotide library. In this review, we highlight the development and therapeutic potential of small molecules inhibiting Th17 cells by targeting RORγt and aptamer mediated CD4(+) T cell specific delivery of small interference RNA against RORγt gene expression to inhibit pathogenic effector functions of Th17 lineage.