PGC-1α pathway dysregulation disrupts myofiber specification in a mouse model of SBMA
Curtis J. Kuo, Laura B. Chopp, Zhigang Yu, Luhan Ni, Hien T. Zhao, Janghoo Lim, Andrew P. Lieberman
Curtis J. Kuo, Laura B. Chopp, Zhigang Yu, Luhan Ni, Hien T. Zhao, Janghoo Lim, Andrew P. Lieberman
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Research Article Muscle biology Neuroscience

PGC-1α pathway dysregulation disrupts myofiber specification in a mouse model of SBMA

Abstract

Skeletal muscle pathology is a critical but poorly understood contributor to neuromuscular degeneration in spinal and bulbar muscular atrophy (SBMA), a CAG/polyglutamine (polyQ) expansion disorder caused by mutation in the androgen receptor (AR). Using a gene-targeted SBMA mouse model, we applied single-nucleus RNA sequencing to identify a disease-specific population of skeletal muscle myonuclei that replaced normal myonuclear subtypes. This transition was associated with dysregulation of the pathway governed by PGC-1α, a central regulator of myofiber specification and metabolic identity. PGC-1α dysfunction in SBMA muscle was age, hormone, and polyQ length dependent and was partially rescued by subcutaneous delivery of AR-targeted antisense oligonucleotides. Integrated ChIP-seq and RNA-seq analyses revealed that aberrant PGC-1α activity promoted the expression of a distinct set of myofiber specification genes while downregulating those that define healthy Type IIb and Type IIx myonuclei. We propose a model in which this dysfunction arose downstream of polyQ-mediated sequestration of PGC-1α cofactors MEF2, CREB, and CBP, leading to transcriptional reprogramming and cellular dysfunction. These findings implicated PGC-1α dysregulation as a key event linking AR polyQ expansion to skeletal muscle degeneration and suggested a shared mechanism for polyQ-mediated muscle pathology across related neurodegenerative diseases.

Authors

Curtis J. Kuo, Laura B. Chopp, Zhigang Yu, Luhan Ni, Hien T. Zhao, Janghoo Lim, Andrew P. Lieberman

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Figure 6

PGC-1α binding to promoters of myonuclei specification genes is altered in AR113Q muscle.

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PGC-1α binding to promoters of myonuclei specification genes is altered ...
(A) Relative gene expression by qPCR of Ppargc1a mRNA in WT, AR21Q, and AR113Q TA at 26 weeks (n = 4 for the WT group, n = 5/group for AR21Q and AR113Q). (B) Relative amount of PGC-1α protein, normalized to vinculin, in WT, AR21Q, and AR113Q TA at 26 weeks (n = 3/group). (C) Expression of Ppargc1a in Type IIb, Type IIb-2, Type IIx, and 113Q-myo myonuclear clusters defined in 52-week AR113Q and WT males by snRNA-seq. (D–F) PGC-1α ChIP-seq was performed on nuclei isolated from the TA of WT and AR113Q males at 26 weeks (n = 4 WT, 7 AR113Q). (D) ChIP-seq results of average occupancy of PGC-1α near known transcription start sites (TSSs) in chromatin extracted from WT and AR113Q TA at 26 weeks (total of 200 mg pooled muscle per genotype). (E) Genes that met magnitude and statistical thresholds in both ChIP-seq differential analysis and bulk RNA-seq of independent cohorts of mice, all obtained from AR113Q vs. WT TA at 26 weeks (ChIP-seq, |log2[FC]| > 1 and FDR < 0.05, n = 4 WT, 7 AR113Q; bulk RNA-seq, |log2[FC] > 0.5849 and Padj < 0.05, n = 4/group). Genes color coded by their presence in the lists of cluster-defining gene (CDG) sets from snRNA-seq data (Figure 1-3): light purple if present in one or more of the Types IIb, IIb-2, and IIx CDG sets, light orange if present in the 113Q-myo CDG set, dark purple/orange if present among the top 25 in any corresponding CDG set. (F) Integrative Genomics Viewer snapshots demonstrating differential enrichment of PGC-1α at promoter regions (highlighted by dashed boxes). Linc-md1 and Casq2 were 2 of the top 25 CDGs for the 113Q-myo cluster. Smox and Tbc1d1 were 2 of the top 25 CDGs in the IIb, IIb-2, and/or IIx clusters. Data are mean ± SD. NS, not significant by 2-way ANOVA with Tukey’s multiple-comparison test. (A) Main ANOVA results: F = 1.632; df = 2; P = 0.2620; Multiple comparisons: WT vs. AR21Q Padj = 0.2831; WT vs. AR113Q Padj = 0.3322; AR21Q vs. AR113Q Padj = 0.9893. (B) Main ANOVA results: F = 1.077; df = 2; P = 0.4224; Multiple comparisons: WT vs. AR21Q Padj = 0.9665; WT vs. AR113Q Padj = 0.4322; AR21Q vs. AR113Q Padj = 0.5491.