Quantitative Peptidomics of Purkinje Cell Degeneration Mice

Iryna Berezniuk,Bradley K Yoder,Raymond C Pasek,Nicolas F Berbari,Juan J Sironi,Lloyd D Fricker,Jonathan Wardman,Hubert Vaudry

doi:10.1371/journal.pone.0060981

Iryna Berezniuk, Bradley K Yoder + Show 6 more

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https://doi.org/10.1371/journal.pone.0060981

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Abstract

Cytosolic carboxypeptidase 1 (CCP1) is a metallopeptidase that removes C-terminal and side-chain glutamates from tubulin. The Purkinje cell degeneration (pcd) mouse lacks CCP1 due to a mutation. Previously, elevated levels of peptides derived from cytosolic and mitochondrial proteins were found in adult pcd mouse brain, raising the possibility that CCP1 functions in the degradation of intracellular peptides. To test this hypothesis, we used a quantitative peptidomics technique to compare peptide levels in wild-type and pcd mice, examining adult heart, spleen, and brain, and presymptomatic 3 week-old amygdala and cerebellum. Contrary to adult mouse brain, young pcd brain and adult heart and spleen did not show a large increase in levels of intracellular peptides. Unexpectedly, levels of peptides derived from secretory pathway proteins were altered in adult pcd mouse brain. The pattern of changes for the intracellular and secretory pathway peptides in pcd mice was generally similar to the pattern observed in mice lacking primary cilia. Collectively, these results suggest that intracellular peptide accumulation in adult pcd mouse brain is a secondary effect and is not due to a role of CCP1 in peptide turnover.

Highlights

In the 1970s, a spontaneous mutant mouse was discovered and named Purkinje cell degeneration due to the loss of cerebellar Purkinje cells starting around 3 weeks after birth [1]
Some of the authors of the present study proposed that Cytosolic carboxypeptidase 1 (CCP1) contributed to peptide degradation based on the dramatic increase in levels of intracellular peptides observed in pcd mice [18]
While these authors had proposed that CCP1 could play a role in tubulin processing, the simplest explanation to account for the increase in peptides derived from intracellular proteins was that these peptides represented substrates of CCP1

Summary

Introduction

In the 1970s, a spontaneous mutant mouse was discovered and named Purkinje cell degeneration (pcd) due to the loss of cerebellar Purkinje cells starting around 3 weeks after birth [1]. A small number of other cell types undergo degeneration in pcd mice, including olfactory bulb mitral cells, retinal photoreceptor cells, and spermatocytes [1]. The mutation responsible for the pcd phenotype was mapped to the gene encoding cytosolic carboxypeptidase 1 (CCP1, known as Nna1), and the gene was named Agtpbp because the protein was initially considered to be an ATP/ GTP binding protein [2]. CCP1 was discovered in a search for mRNAs upregulated in spinal motor neurons during regeneration after axotomy [3]. CCP1 is linked to both degeneration and regeneration. CCP1 is the most abundant of the CCPs in mouse brain [4]

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