Renal proximal tubular cells acquire resistance to cell death stimuli in mice with hereditary tyrosinemia type 1

Abstract

Background. Hereditary tyrosinemia type 1 (HT1), which is associated with severe liver and kidney damage, is caused by deficiency of fumarylacetoacetate hydrolase (FAH), the last enzyme of the tyrosine breakdown cascade. HT1-associated liver and kidney failure can be prevented by blocking an enzyme upstream of FAH in the tyrosine breakdown pathway with 2-(2-nitro-4- trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC). FAH knockout mice develop the HT1 phenotype when NTBC treatment is discontinued. Methods. The occurrence of cell death was investigated in kidneys of Fah-l- mice on and off NTBC either unchallenged or injected with 800 mg/kg of homogentisic acid (HGA), an intermediate of tyrosine breakdown. Results. No cell death could be detected in kidneys of Fah-l- mice on NTBC. A slight increase of cleaved caspase-3 was the only apoptosis-related feature that could be detected in kidneys of Fah-/- mice off NTBC. Challenge of Fah-/- mice on NTBC with HGA led to massive death of renal proximal tubular cells, with positive terminal deoxynucleotidyl transferase-mediated deoxyuridine diphosphate (dUDP) nick-end labeling (TUNEL) and DNA fragmentation assays, but hardly any cleavage of caspase-9 and caspase-3. Fah-l- mice off NTBC acquired resistance to HGA-induced renal cell death and the kidneys exhibited relatively few features of apoptosis upon challenge with HGA, with a small increase in expression of cleaved caspase-9 and caspase-3. Conclusion. Kidneys of adult Fah-/- mice, withdrawn from NTBC for 15 days, reveal limited characteristics of apoptosis, and have acquired resistance to a caspase-9- and caspase-3-independent form of cell death provoked by HGA.