Proprioception, the perception of body and limb position, is mediated by proprioceptors, specialized mechanosensory neurons that convey information about the stretch and tension experienced by muscles, tendons, skin and joints. In mammals, the molecular identity of the stretch-sensitive channel that mediates proprioception is unknown. We found that the mechanically activated nonselective cation channel Piezo2 was expressed in sensory endings of proprioceptors innervating muscle spindles and Golgi tendon organs in mice. Two independent mouse lines that lack Piezo2 in proprioceptive neurons showed severely uncoordinated body movements and abnormal limb positions. Moreover, the mechanosensitivity of parvalbumin-expressing neurons that predominantly mark proprioceptors was dependent on Piezo2 expression in vitro, and the stretch-induced firing of proprioceptors in muscle-nerve recordings was markedly reduced in Piezo2-deficient mice. Together, our results indicate that Piezo2 is the major mechanotransducer of mammalian proprioceptors.
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We thank B. Coste (Aix Marseille Université) for suggestions and H.U. Zeilhofer (University of Zurich) and R. Seal (University of Pittsburgh) for providing HoxB8-Cre mice. This work was supported by the Howard Hughes Medical Institute and US National Institutes of Health grant R01DE022358.
The authors declare no competing financial interests.
Integrated supplementary information
Supplementary Figure 1 Characterization of mechanically activated currents and Piezo2 expression in proprioceptive neurons.
a, Pvalb immunostaining with tdTomato epifluorescence in lumbar DRG from adult Pvalb-Cre;Ai9 mice. Scale bar: 100 μm. b, Current (I)-voltage (V) relationship of one mechanically activated IA current found in tdTomato+ neurons from adult Pvalb-Cre;Ai9 DRG. Voltage clamp experiments conducted identically to those depicted in Fig. 1b and c. Mechanically activated current responses to threshold plus 4-5 µm were used for I-V measurements.
Supplementary Figure 2 Characterization of GFP expression in Piezo2GFP lumbar DRG and skeletal muscles from hind leg.
a, Immunofluorescence for GFP and Pvalb in adult Piezo2GFP lumbar DRG. Circles mark cell bodies that co-express GFP and Pvalb. b, Immunofluorescence for GFP and Vglut1 in MSs and GTOs in various skeletal muscles from P8 Piezo2GFP hind leg. c, Immunofluorescence for GFP and αBTX (a marker of neuromuscular junction) in P6 Piezo2GFP hind leg muscle. Scale bars: a, 100 μm; b, 50 μm; c, 20 μm.
a, Based on caudal bias in the HoxB8-Cre activity, we assessed tdTomato epifluorescence in cervical/upper thoracic (left), lower thoracic (middle), and lumbar (right) DRG. tdTomato expression was sparse in neuronal cell bodies of cervical/upper thoracic (Th1-3) DRG stained with Piezo2 antibody (left). Strong tdTomato expression was detected in a majority of neuronal cell bodies in lower thoracic (middle) and lumbar (right) DRG stained with Piezo2 and Pvalb antibodies. White arrowheads mark tdTomato-cell bodies that express Piezo2 and Pvalb. This indicates that 1.5% (12/806) of total DRG neurons do not express HoxB8-Cre. b, tdTomato epifluorescence with Vglut1 immunostaining in proprioceptor endings in forelimb (left) and hind limb (right) muscles of adult HoxB8-Cre;Ai9 reporter. tdTomato was detected in MS endings and skeletal muscles of hind limbs, while it was absent in forelimb muscles and associated MSs. c, tdTomato epifluorescence with Nefh and DAPI staining in lanceolate endings (left, hair follicle) and with Nefh staining in Merkel cell-neurite complexes (right, touch dome) in adult HoxB8-Cre;Ai9 dorsal skin. Dotted line on left indicates the hair follicle, and the bracket marks lanceolate endings. Dotted circles on right mark Merkel cells, and the dotted line marks the epidermal-dermal junction. HS, hair shaft; TD, touch dome; GH, guard hair. Scale bars: a, 100 μm; b, 50 μm; c, 20 μm.
a, b, Piezo2 (green puncta) and Pvalb (red puncta) dual in situ hybridization in lumbar DRG of adult Piezo2fl/+ (WT, a) and Pvalb-Cre;Piezo2cKO mice (b). Left panels show entire DRG. Middle panels are the magnified view of dotted insets in the left panels. Smaller panels on right show the magnified view of the area marked with orange lines. White arrowheads in WT DRG (a) indicate Pvalb+ cell bodies with intact Piezo2. White circles in cKO DRG (b) indicate Pvalb+ cell bodies without Piezo2. White asterisk indicates one Pvalb+ cell body with intact Piezo2. 11.2% of Pvalb+ DRG neurons (10/89) still retained Piezo2 in Pvalb-Cre;Piezo2cKO mice. c, Quantification of MSs found in EDL (extensor digitorum longus) and soleus muscles from P10-11 WT and Pvalb-Cre;Piezo2cKO mice. Bars represent mean ± s.e.m. ns, not statistically significant. Unpaired t-test with Welch’s correction. d, Example images of Vglut1-stained MSs found in P30 WT and Pvalb-Cre;Piezo2cKO mice. e, Central projection of tdTomato+ proprioceptors in lumbar spinal cord of P5 Pvalb-Cre;Ai9 (WT) and Pvalb-Cre;Ai9;Piezo2cKO mice. Scale bars: a, b, e, 100 μm; d, 20 μm.
a, Piezo2 remaining (%) in cervical/upper thoracic (left) and lumbar (right) DRG from adult Piezo2fl/+ (WT) and HoxB8-Cre;Piezo2cKO mice by qRT-PCR. Note that HoxB8-Cre;Piezo2cKO mice refer to HoxB8-Cre;Piezo2fl/– (only one allele of Piezo2 is present prior to Cre recombination). Bars represent mean ± s.e.m. **P < 0.01; ****P < 0.0001. Unpaired t-test with Welch’s correction. b, Piezo2 (green puncta) in situ hybridization in lumbar DRG of adult Piezo2fl/+ (WT, top) and HoxB8-Cre;Piezo2cKO mice (bottom). Left panels show entire DRG outlined by solid lines. Right panels show the magnified view of dotted insets in the left panels. White asterisk (bottom, right) indicates one cell body with intact Piezo2. 1.2% of lumbar DRG neurons (2/165) still retained Piezo2 in HoxB8-Cre;Piezo2cKO mice, and this likely suggests that 1.2% of lumbar DRG neurons do not express HoxB8-Cre. c, Central projection of proprioceptors via Pvalb staining in lumbar spinal cord of P5 Piezo2fl/+ (WT) and HoxB8-Cre;Piezo2cKO mice. Scale bars: b, c, 100 μm.
Supplementary Figure 7 Activation of putative group III/IV acid-sensitive sensory neurons by pH 6.0 lactic acid in adult WT and Piezo2 cKO muscles.
Note that both Pvalb-Cre;Piezo2cKO and HoxB8-Cre;Piezo2cKO lines responded similarly. a, A typical WT response to pH 6.0 lactic acid with baseline firing activity. b, Lactic acid response in Piezo2 cKO mouse with no baseline firing activity.
Supplementary Figures 1–7 and Supplementary Tables 1 and 2 (PDF 6102 kb)
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Woo, S., Lukacs, V., de Nooij, J. et al. Piezo2 is the principal mechanotransduction channel for proprioception. Nat Neurosci 18, 1756–1762 (2015). https://doi.org/10.1038/nn.4162
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