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MicroRNA pathways Modulate Polyglutamine-induced Neurodegeneration

MicroRNA pathways Modulate Polyglutamine-induced Neurodegeneration. Julide Bilen, Nan Liu, Barrington G. Burnett, Randall N. Pitman, and Nancy M. Borris Molecular Cell, October 6, 2006 Christine Marciniak February 21, 2008. Background – Human polyQ diseases & MicroRNAs.

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MicroRNA pathways Modulate Polyglutamine-induced Neurodegeneration

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  1. MicroRNA pathways Modulate Polyglutamine-induced Neurodegeneration Julide Bilen, Nan Liu, Barrington G. Burnett, Randall N. Pitman, and Nancy M. Borris Molecular Cell, October 6, 2006 Christine Marciniak February 21, 2008

  2. Background – Human polyQ diseases & MicroRNAs • Expansion in CAG repeats • Dominant toxicity → Neuronal dysfunction & loss • Pathogenic protein accumulates in nuclear inclusions • Some hallmarks of programmed cell-death seen • (Condensation of nucleaus & cytoplasm) • Spinocerebeller ataxia type 3 (SCA3) • miRNAs – shown to regulate programmed cell-death genes in Drosophilia • Do miRNAs play a role in neurodegeneration?

  3. Ataxin-3 Degeneration in the fly eye • Weak (Q61) or partial (Q78 or Q84) Poly-Q induced degeneration • Loss of Dicer-1 (or R3D1) leads to enhancement of Poly-Q induced degeneration (miRNA pathway affected) • Loss of Dicer-1 (or R3D1) ALONE does not lead to degeneration • Loss of Dicer-2 does not affect Poly-Q induced degeneration (siRNA pathway not affected) External Eyes Hoechst Staining Retinal Thickness External Eyes & Retinal Thickness

  4. Ataxin-3 Toxicity in Human Cells Control siRNA or siRNA to dicer Short poly-Q repeat (Q29) *Significant increase in cell death in dicer-knockdown treated cells with expansion *Significant mitigation of cell death in similar cells also treated with purified small RNA fraction Expanded poly-Q repeat (Q72) No toxicity after 24hrs Enhanced cell death with no Dicer

  5. miRNA bantam modulates Ataxin-3 toxicity Genomic region of ban Psuedopupil Assay Neurol Loss enhanced with loss of ban Suppression of Poly-Q toxicity by overexpression of ban External fly eye and Internal retinal sections

  6. ban miRNA suppresses degeneration downstream of polyQ toxicity Immunostaining in 7-day flies for stress-induced Hsp-70 Endogenous stress response not altered by ban 4-hour vs. 7-day flies Diffuse Accumulated in nuclear inclusions polyQ protein Western immunoblot for stress-induced Hsp-70 Endogenous stress response not altered by ban 7-day flies Coexpression: ban has no effect human Hsp-70 reduces accumulation

  7. Main conclusions • If miRNAs are gone, more degeneration is observed • Knockdown of dicer – observed in polyQ disease SCA3 degenerated fly eye and cultured human cells • Specific miRNAs are involved in the regulated pathway to modulate polyQ toxicity • bantam miRNA • NOT siRNAs! (Dicer-2 not affected in fly eye)

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