Pharmacological rescue of carnitine transport in primary carnitine deficiency

Authors

  • Cristina Amat di San Filippo,

    1. Division of Medical Genetics, Department of Pediatrics, University of Utah, Salt Lake City, Utah
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  • Marzia Pasquali,

    1. Department of Pathology, University of Utah, Salt Lake City, Utah
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  • Nicola Longo

    Corresponding author
    1. Division of Medical Genetics, Department of Pediatrics, University of Utah, Salt Lake City, Utah
    2. Department of Pathology, University of Utah, Salt Lake City, Utah
    • Division of Medical Genetics, Department of Pediatrics, University of Utah, 2C412 SOM, 50 North Medical Drive, Salt Lake City, UT 84132
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  • Communicated by Nancy Spinner

  • This article is a US Government work and, as such, is in the public domain in the United States of America.

Abstract

Primary carnitine deficiency is a recessive disorder caused by heterogeneous mutations in the SLC22A5 gene encoding the OCTN2 carnitine transporter. Here we extend mutational analysis to eight new families with this disorder. To determine the mechanism by which missense mutations impaired carnitine transport, the OCTN2 transporter was tagged with the green fluorescent protein and expressed in CHO cells. Analysis by confocal microscopy indicated that several missense mutants (M1I, R169W, T232 M, G242 V, S280F, R282Q, W283R, A301D, W351R, R399Q, T440 M, E452 K, and T468R) matured normally to the plasma membrane. By contrast, other mutations (including R19P, ΔF22, R83L, S280F, P398L, Y447C, and A142S/R488 H) caused significant retention of the mutant OCTN2 transporter in the cytoplasm. Failed maturation to the plasma membrane is a common mechanism in disorders affecting membrane transporters/ion channels, including cystic fibrosis. To correct this defect, we tested whether drugs reducing the efficiency of protein degradation in the endoplasmic reticulum (ER) (phenylbutyrate, curcumin) or capable of binding the OCTN2 carnitine transporter (verapamil, quinidine) could improve carnitine transport. Prolonged incubation with phenylbutyrate, quinidine, and verapamil partially stimulated carnitine transport, while curcumin was ineffective. These results indicate that OCTN2 mutations can affect carnitine transport by impairing maturation of transporters to the plasma membrane. Pharmacological therapy can be effective in partially restoring activity of mutant transporters. Hum Mutat 27(6), 513–523, 2006. Published © 2006 Wiley-Liss, Inc.

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