Abstract
The Long-Evans Agouti (LEA/Tohm) rat has recently been established as a new rat model of type 2 diabetes. The onset of diabetes mellitus was observed only in male LEA/Tohm rats; however, urinary glucose appeared before the onset of diabetes. To clarify the genetic basis of urinary glucose, we performed genetic linkage analysis using (BN × LEA) F2 intercross progeny. A recessively acting locus responsible for urinary glucose excretion (ugl) was mapped to a 7.9 Mb region of chromosome 10, which contains the cystinosin (Ctns) gene. The Ctns gene encodes the cystine transporter, which transports cystine out of the lysosome and is responsible for nephropathic cystinosis in humans. Sequence analysis identified a 13-bp deletion in the Ctns gene, leading to a truncated and loss-of-function protein, which cause cystine accumulation in various tissues. We also developed a novel congenic rat strain harboring the Ctnsugl mutation on the F344 genetic background. Phenotypic analysis of F344-Ctnsugl rats indicated that the incidence of urinary glucose was 100% in both males and females at around 40 weeks of age, and marked cystine accumulation was observed in the tissues, as well as remarkable renal lesions and cystine crystals in the lysosomes of the renal cortex. Furthermore, treatment with cysteamine depleted the cystine contents in F344-Ctnsugl rat embryonic fibroblasts. These results indicated that the F344-Ctnsugl rat provides a novel rat model of cystinosis, which allows not only a better understanding of the pathogenesis and pathophysiology of cystinosis but will also contribute to the development of new therapies.
Highlights
Cystinosis is a rare progressive lysosomal storage disorder characterized by the accumulation of cystine in lysosomes throughout every cell in the body
Whole genome scan was performed in 47 F2 progeny using 201 SSLP markers as shown in Supplemental Table S1 a Rattus norvegicus (Norway rat) genome assembly Rnor_6.0 b F2 rats having urine glucose lower than 50 mg/dL under fasting conditions c F2 rats having urine glucose higher than 50 mg/dL under fasting conditions coding exons and encodes 367 amino acids, we identified a 13-bp deletion at position 525 (c.525_537del) in exon 7 of Ctns in LEA/Tohm rats (Fig. 1a), causing a frame shift mutation at codon 177 with subsequent termination after an additional 17 codons
We present several lines of evidence demonstrating that a mutation in the Ctns gene underlies spontaneous renal glucosuria in LEA/Tohm rats
Summary
Cystinosis is a rare progressive lysosomal storage disorder characterized by the accumulation of cystine in lysosomes throughout every cell in the body. This results in various clinical characteristics such as Fanconi syndrome, poor growth, photophobia, hypothyroidism, end-stage renal disease (ESRD), hypothyroidism, hypogonadism, muscle weakness, swallowing difficulties, and pulmonary dysfunction. Cystinosis is an autosomal recessive disorder caused by mutations that disable the cystine transporter called cystinosin (CTNS) (Town et al 1998; Touchman et al 2000). Cystine (which is the oxidized dimer form of cysteine) accumulates continuously in the lysosome owing to the defective CTNS, resulting in the formation of cystine crystals in every cell in the body, leading to multi-organ damage. It is estimated that the frequency of cystinosis is 1 in 100,000–200,000 live births (Elmonem et al 2016; Gahl et al 2002); the incidence in East Asia is much lower (Chuang et al 2012; Higashi et al 2017; Yang et al 2015) because the disease is often undiagnosed or misdiagnosed
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