Disruption ofPPT2in mice causes an unusual lysosomal storage disorder with neurovisceral features

Abstract

The palmitoyl protein thioesterase-2 (PPT2) gene encodes a lysosomal thioesterase homologous to PPT1, which is the enzyme defective in the human disorder called infantile neuronal ceroid lipofuscinosis. In this article, we report that PPT2 deficiency in mice causes an unusual form of neuronal ceroid lipofuscinosis with striking visceral manifestations. All PPT2-deficient mice displayed a neurodegenerative phenotype with spasticity and ataxia by 15 mo. The bone marrow was infiltrated by brightly autofluorescent macrophages and multinucleated giant cells, but interestingly, the macrophages did not have the typical appearance of foam cells commonly associated with other lysosomal storage diseases. Marked splenomegaly caused by extramedullary hematopoiesis was observed. The pancreas was grossly orange to brown as a result of massive storage of lipofuscin pigments in the exocrine (but not islet) cells. Electron microscopy showed that the storage material consisted of multilamellar membrane profiles (''zebra bodies''). In summary, PPT2 deficiency in mice manifests as a neurodegenerative disorder with visceral features. Although PPT2 deficiency has not been described in humans, manifestations would be predicted to include neurodegeneration with bone marrow histiocytosis, visceromegaly, brown pancreas, and linkage to chromosome 6p21.3 in affected families. P almitoyl protein thioesterase (PPT) 2 is a lysosomal thioesterase that is 27% identical to PPT1, a lysosomal enzyme defective in a neurodegenerative disorder called infantile neuronal ceroid lipofuscinosis, or infantile Batten disease (1). The neuronal ceroid lipofuscinosis (NCLs) are a group of neurodegenerative disorders of children characterized by the accumulation of autofluorescent storage material in the brain and other tissues, cognitive and motor deterioration, visual failure, and seizures. Notable is the absence of functionally significant manifestations outside the central nervous system (2, 3). The NCLs are caused by defects in at least eight genes (of which six have been identified), and different forms of the disease have a distinct storage ultrastructure (2). The PPT1 or CLN1 gene underlies the most severe form of the disease, and it encodes a thioesterase enzyme that removes palmitate or other fatty acids from cysteine residues in proteins (4-6). The enzyme encoded by PPT2 is a second lysosomal thioesterase with a substrate specificity that overlaps that of PPT1 (7-9).Recently, we disrupted both PPT1 and PPT2 genes in mice and showed that homozygous PPT1 knockout mice have a neurodegenerative disorder that closely parallels infantile Batten disease (10). Most PPT1 knockout mice are terminal by 10 mo of age. Preliminary analysis of homozygous PPT2 knockout mice at 10 mo had shown the development of scant autofluorescent storage material in the brain and a neurological phenotype in a proportion of the animals. In the current article, we have extended the observation of these PPT2 knockout mice throughout their natural lifespan and analyzed their behavio...

A murine model of infantile neuronal ceroid lipofuscinosis - Ultrastructural evaluation of storage in the central nervous system and viscera

“…At necropsy, none of the mice had enlarged spleens or pancreases as has been described in another PPT deficient mouse model (19), and there were no gross abnormalities seen. The PPT1 −/− mice accumulated membrane-bound GROD in multiple sites including brain, eye, liver, spleen, heart, aorta, peripheral nerve and kidney ( Table 1).…”

The Metabolic Serine Hydrolases and Their Functions in Mammalian Physiology and Disease

“…532 PPT2(−/−) mice develop an unusual variant of neuronal ceroid lipofuscinosis that, in addition to causing neurological dysfunction, also strongly affects peripheral tissues. 533 PPT2(−/−) mice show a clasping phenotype in the tail suspension test with a slower onset than what is observed in PPT1(−/−) mice. Similarly, the lifespan of PPT2(−/−) mice is two years, longer than that of PPT1(−/−) mice but still significantly shorter than wild-type mice, and, at death, PPT2(−/−) brains are ~10% lighter than wild-type controls and show cerebral cortical atrophy and scattered apoptotic bodies.…”

Dynamic Palmitoylation and the Role of DHHC Proteins in T Cell Activation and Anergy

“…The degree of crossreactivity between PPT1 and PPT2 is unclear. Importantly, however, mice lacking PPT1 or PPT2 display a similar lysosomal storage disease, but an apparently intact immune system (Gupta et al, 2001; Gupta et al, 2003). The difference in severity might be explained by other unannotated substrates that are not detected by [ 35 S]Cys labeling.…”