Fig. 8: Restoring spindle structure and function in aged mice by LRP4 expression.

a Representative images of EDL muscles of 3 M, 12 M, and 24 M-old mice, whole mount stained with 555-anti-LRP4 (red) and NF/Syn (blue). Arrowheads, non-annulospiral axons had no LRP4 expression. Arrows, LRP4 negative annulospiral endings in aged mice. Scale bar, 10 µm. b Quantification of the relative intensity of LRP4; t ₍₂₀₎ = 9.063, ***p < 0.0001; t ₍₂₀₎ = 4.34, ***p = 0.0003. n = 11 muscle spindles from 3 mice per group, unpaired two-tailed t test. c Quantitative RT-PCR tested the relative expression of Lrp4 mRNA in 3 M, 12 M or 24 M mice; t ₍₄₎ = 5.861, **p = 0.004; t ₍₄₎ = 4.006, *p = 0.016. n = 3 mice per group, unpaired two-tailed t test. d Expression of Flag-LRP4 in skeletal muscle was confirmed by Western blotting. Uncropped blots in Source Data. e Quantification of longest running time on rotating rod between WT and Flag-Lrp4 mice at indicated age. f Quantification of side slips in beam walking task of WT and Flag-Lrp4 mice at indicated age; t ₍₁₈₎ = 2.251, *p = 0.037. g Quantification of time required for beam walking task; t ₍₁₈₎ = 2.793, *p = 0.012. n = 10 mice per group, unpaired two-tailed t test in (e–g). h Representative images of muscle spindle in EDL muscles of 24 M-old mice, whole mount stained with NF/Syn (green) and α-BTX (red). Arrowhead, bleb of axon; arrows, annulospiral endings. Scale bars, 100 µm and 20 µm. i Quantification of unraveling muscle spindle in each group; t ₍₄₎ = 5.584, **p = 0.005. j Quantification of the incidence of axon with large blebs in each group; t ₍₄₎ = 9.55, ***p = 0.0007. n = 3 mice per group, unpaired two-tailed t test in (i) and (j). The distribution of mean axon width (k) and inter-rotational distance (l) in aged WT and Flag-Lrp4 mice. Data are shown as mean ± SEM, n = 3 mice per group. Source data are provided as a Source Data file.