BACKGROUND: In the renal hypertrophy that occurs in diabetes mellitus, decreased 
proteolysis may lead to protein accumulation, but it is unclear which proteins 
are affected. Because the lysosomal proteolytic pathway of chaperone-mediated 
autophagy is suppressed by growth factors in cultured cells, we investigated 
whether the abundance of substrates of this pathway increase in diabetic 
hypertrophy.
METHODS: Rats with streptozotocin (STZ)-induced diabetes were pair-fed with 
vehicle-injected control rats. Proteolysis was measured as lysine release in 
renal cortical suspensions and protein synthesis as phenylalanine incorporation. 
Target proteins of chaperone-mediated autophagy were measured in cortical 
lysates and nuclear extracts by immunoblot analysis. Proteins that regulate 
chaperone-mediated autophagy [the lysosomal-associated membrane protein 2a 
(LAMP2a) or the heat shock cognate protein of 73 kD (hsc-73)] were measured in 
lysosomes isolated by density gradient centrifugation.
RESULTS: Proteolysis decreased by 41% in diabetic rats; protein synthesis 
increased at 3 days, but returned to baseline by 7 days. The abundance of 
proteins containing that chaperone-mediated autophagy KFERQ signal motif 
increased 38% and individual KFERQ containing proteins [e.g., M2 pyruvate 
kinase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and pax2] were more 
abundant. LAMP2a and hsc73 decreased by 25% and 81%, respectively, in cortical 
lysosomes from diabetic vs. control rats.
CONCLUSION: The decline in proteolysis in acute diabetes mellitus is associated 
with an increase in proteins degraded by chaperone-mediated autophagy and a 
decrease in proteins which regulate this pathway. This study provides the first 
evidence that reduced chaperone-mediated autophagy contributes to accumulation 
of specific proteins in diabetic-induced renal hypertrophy.