Prohormone convertase 2 activity is increased in the hippocampus of Wfs1 knockout mice.

Karin Tein,Anton Terasmaa,Eero Vasar,Sergo Kasvandik,Sulev Kõks

doi:10.3389/fnmol.2015.00045

Abstract

Background: Mutations in WFS1 gene cause Wolfram syndrome, which is a rare autosomal recessive disorder, characterized by diabetes insipidus, diabetes mellitus, optic nerve atrophy, and deafness. The WFS1 gene product wolframin is located in the endoplasmic reticulum. Mice lacking this gene exhibit disturbances in the processing and secretion of peptides, such as vasopressin and insulin. In the brain, high levels of the wolframin protein have been observed in the hippocampus, amygdala, and limbic structures. The aim of this study was to investigate the effect of Wfs1 knockout (KO) on peptide processing in mouse hippocampus. A peptidomic approach was used to characterize individual peptides in the hippocampus of wild-type and Wfs1 KO mice.Results: We identified 126 peptides in hippocampal extracts and the levels of 10 peptides differed between Wfs1 KO and wild-type mice at P < 0.05. The peptide with the largest alteration was little-LEN, which level was 25 times higher in the hippocampus of Wfs1 KO mice compared to wild-type mice. Processing (cleavage) of little-LEN from the Pcsk1n gene product proSAAS involves prohormone convertase 2 (PC2). Thus, PC2 activity was measured in extracts prepared from the hippocampus of Wfs1 KO mice. The activity of PC2 in Wfs1 mutant mice was significantly higher (149.9 ± 2.3%, p < 0.0001, n = 8) than in wild-type mice (100.0 ± 7.0%, n = 8). However, Western blot analysis showed that protein levels of 7B2, proPC2 and PC2 were same in both groups, and so were gene expression levels.Conclusion: Processing of proSAAS is altered in the hippocampus of Wfs1-KO mice, which is caused by increased activity of PC2. Increased activity of PC2 in Wfs1 KO mice is not caused by alteration in the levels of PC2 protein. Our results suggest a functional link between Wfs1 and PC2. Thus, the detailed molecular mechanism of the role of Wfs1 in the regulation of PC2 activity needs further investigation.

Highlights

Wolfram syndrome (WS) was first described by Wolfram and Wagener (1938) and is a rare autosomal recessive disorder characterized by diabetes insipidus (DI), diabetes mellitus (DM), optic nerve atrophy (OA), and deafness (D) – DIDMOAD (Strom et al, 1998)
Most of the identified peptides were derived from 11 precursor sequences: galanin; orexin/hypocretin; neuropeptide Y; proprotein convertase subtilisin/kexin type 1 inhibitor; preprodynorphin; proenkephalin-A; melaninconcentrating hormone; prepronociceptin; neuroendocrine protein 7B2; substance P and teneurin-1
The levels of 10 peptides were found to be different in Wfs1 KO versus wild-type mice (Table 1)

Summary

Introduction

Wolfram syndrome (WS) was first described by Wolfram and Wagener (1938) and is a rare autosomal recessive disorder characterized by diabetes insipidus (DI), diabetes mellitus (DM), optic nerve atrophy (OA), and deafness (D) – DIDMOAD (Strom et al, 1998). Patients without WS, but exhibiting bipolar disease, major depression, and schizophrenia have been found to carry mutations in WFS1 gene (Strom et al, 1998; Evans et al, 2000; Torres et al, 2001; Crawford et al, 2002). Wfs protein is located in the membrane of the endoplasmic reticulum (ER), where it forms ∼400 kDa protein complexes (Hofmann et al, 2003). Mutations in WFS1 gene cause Wolfram syndrome, which is a rare autosomal recessive disorder, characterized by diabetes insipidus, diabetes mellitus, optic nerve atrophy, and deafness. The WFS1 gene product wolframin is located in the endoplasmic reticulum. Mice lacking this gene exhibit disturbances in the processing and secretion of peptides, such as vasopressin and insulin. A peptidomic approach was used to characterize individual peptides in the hippocampus of wild-type and Wfs KO mice

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