Spinal injection of newly identified cerebellin-1 and cerebellin-2 peptides induce mechanical hypersensitivity in mice.

By screening for neuropeptides in the mouse spinal cord using mass spectrometry (MS), we have previously demonstrated that one of the 78 peptides that is expressed predominantly (> 6-fold) in the dorsal horn compared to the ventral spinal cord is the atypical peptide desCER [des-Ser1]-cerebellin, which originates from the precursor protein cerebellin 1 (CBLN1). Furthermore, we found that intrathecal injection of desCER induces mechanical hypersensitivity in a dose dependent manner. The current study was designed to further investigate the relative expression of other CBLN derived peptides in the spinal cord and to examine whether they share similar nociceptive properties. In addition to the peptides cerebellin (CER) and desCER we identified and relatively quantified nine novel peptides originating from cerebellin precursor proteins CBLN1 (two peptides), CBLN2 (three peptides) and CBLN4 (four peptides). Ten out of eleven peptides displayed statistically significantly (p < 0.05) higher expression levels (200-350%) in the dorsal horn compared to the ventral horn. Intrathecal injection of three of the four CBLN1 and two of the three CBLN2 derived peptides induced mechanical hypersensitivity in response to von Frey filament testing in mice during the first 6 h post-injection compared to saline injected mice, while none of the four CBLN4 derived peptides altered withdrawal thresholds. This study demonstrates that high performance MS is an effective tool for detecting novel neuropeptides in CNS tissues. We show the presence of nine novel atypical peptides originating from CBLN1, CBLN2 and CBLN4 precursor proteins in the mouse dorsal horn, whereof five peptides induce pain-like behavior upon intrathecal injection. Further studies are required to investigate the mechanisms by which CBLN1 and CBLN2 derived peptides facilitate nociceptive signal transmission.