Nutrition and Metabolic Insights

Background/Aims: We have previously isolated a novel lysosomal cysteine protease, cathepsin Y, which produces a kinin-potenciating octapeptide from rat plasma. The present study aimed to elucidate the influence of protein-restriction on cathepsin Y mRNA expression in tissues of growing rat.

Methods: Weaning rats were fed either 20% casein (normal-protein, NP) or 5% casein (low-protein, LP) diet for 12 weeks, from post-weaning period to maturity. Cathepsin Y mRNA expression in tissues was examined using RT-PCR and compared with that of cathepsin L, a general marker of muscle atrophy.

Results: Body, liver and spleen weights and diet intake of LP were significantly lower than those of NP. Cathepsin Y expression in LP was increased in liver (3.70 fold vs. NP) and spleen (1.28 fold) at early periods of protein-restriction, whereas that of cathepsin L was increased in liver and pectoral muscle through all intake periods. However, significant differences were detected in neither cathepsin Y expression in pectoral muscle nor cathepsin L expression in spleen throughout intake periods.

Conclusions: A significant up-regulation of cathepsin Y was observed in spleen and liver, suggesting that it may associate with immunodepression in rats under protein-malnutrition during the early post-weaning period.