Variant proteins in ovine ceroid-lipofuscinosis

Submitochondrial distribution and delayed proteolysis of subunit c of the H+-transporting ATP-synthase in ovine ceroid-lipofuscinosis

The neuronal ceroid-lipofuscinose (NCL) are recessively inherited lysosomal storage diseases in children and animals. The major stored protein in many of these diseases is subunit c of the mitochondrial inner membrane H+-transporting ATP-synthase. Previous studies of naturally occurring ovine ceroid-lipofuscinosis (OCL) in South Hampshire sheep showed that the genes and transcripts for subunit c were normal and inferred that this protein was expressed normally in mitochondria prior to storage in lysosomes. Accumulation in mitochondria has not been conclusively established and we have therefore used the South Hampshire model to demonstrate approximately 1.8-fold normal levels of subunit c in mitochondrial inner membranes prepared from liver. Other mitochondrial inner membrane and ATP-synthase proteins that could be detected by mass spectrometry (MS) or two-dimensional electrophoresis (2-DE) were present in normal amounts. The accumulating subunit c showed normal post-translational modification but was abnormally resistant to proteolysis. These results are consistent with the hypothesis that OCL may result from a mitochondrial disorder that affects turnover of correctly expressed subunit c, although we cannot exclude the possibility that a postmitochondrial defect delays processing of subunit c out of mitochondria.

The mannosidoses and ceroid-lipofuscinoses: experimental studies on two types of storage disease

alpha-Mannosidosis of Angus calves was studied both for its veterinary importance and as a model of analogous human lysosomal storage diseases. This study facilitated a similar study in Australia on Swainsona spp. intoxication of livestock in which the toxic principle was shown to be an indolizidine alkaloid, Swainsonine. These genetic and acquired alpha-mannosidoses are compared with beta-mannosidosis. Collectively the study has helped the understanding of the processes of glycosylation and catabolism of glycoproteins. An experiment of nature involving an alpha-mannosidosis chimeric calf born co-twin to a normal calf helped to define the expectations and limitations of bone marrow transplants in this type of storage disease in humans. The inherited ceroid-lipofuscinoses (Batten disease) were studied in an ovine model. Isolation and analyses of the fluorescent accumulated lipopigment denied the dogma of lipid peroxidation current in the 1970s and 1980s. It was shown that in this, and analogous diseases in humans, the dominantly accumulated species was the very hydrophobic protein, subunit c of mitochondrial ATP synthase. Contrary to the adage that this should reflect a disorder of lysosomal proteolysis, there is accumulating evidence that the primary defect resides in mitochondria. Because of its hydrophobic nature, subunit c forms paracrystaline complexes which appear resistant to proteolysis within the lysosomal apparatus.

Brain lysosomal hydrolases in neuronal ceroid-lipofuscinoses

Although the neuronal ceroid-lipofuscinoses (NCLs) are often referred to as lysosomal storage disorders, information on brain lysosomal hydrolases in NCLs is not available. We have determined the specific activities of several acid hydrolases in postmortem brain gray matter of infantile (INCL), late infantile (LINCL), juvenile (JNCL), and adult (ANCL) forms of NCL, patients affected with other neurological disorders (ON), and normal controls. The specific activities of beta-hexosaminidase A and B were significantly high in JNCL gray matter, whereas in LINCL, the increase is significant only in beta-hexosaminidase compared to the controls. A significant increase in the activities of alpha-mannosidase, beta-glucuronidase, and acid phosphatase was also observed in LINCL and JNCL patients compared to the control values. beta-galactosidase activity was also found to be elevated in JNCL brains over the controls. In contrast, activities of beta-glucosidase and sialidase appeared to be lowered in INCL and LINCL. On the other hand, alpha-fucosidase, beta-mannosidase, and sulfatase were unaffected in NCLs brains. Thus, the present data indicate NCLs related abnormalities in some of the acid hydrolases in brain gray matter, which are primarily glycoproteins of lysosomal origin. These data in conjuction with the reported association of sphingolipid activator proteins (SAP) A and D and lysosomal glycoproteins with NCL storage bodies imply abberations in the glycoconjugate metabolism and lysosomal function.

Batten disease (ceroid-lipofuscinosis): the enigma of subunit c of mitochondrial ATP synthase accumulation

Ceroid-lipofuscinosis is an inherited neurodegenerative disease of human beings and domestic animals characterized by the accumulation in neurons and other cells of a fluorescent lipopigment. In the ovine form of disease, subunit c of mitochondrial ATP synthase is the dominant accumulated metabolite ( > 50%). It also accumulates significantly in the late infantile and juvenile forms of the human disease and several other animal forms. Evidence is accumulating that the underlying biochemical defect may be associated with mitochondria. The extreme hydrophobicity of subunit c and its propensity to aggregate with lipids into regular multilamellar arrays that cannot be catabolised may reflect an initial defect not necessarily associated with faulty proteolysis. This hypothesis extends an earlier one that subunit c accumulated due to a defect in its catabolic pathway.

Batten disease and the ATP synthase subunit c turnover pathway: raising antibodies to subunit c

Analysis of storage bodies in the ceroid-lipofuscinoses (Batten disease) has demonstrated a high protein content suggestive of a proteinosis. Direct N-terminal sequencing has shown that subunit c of mitochondrial ATP synthase is specifically stored in the disease in sheep and cattle, and in the human late infantile and juvenile diseases, as well as in 3 breeds of dogs. No differences have been found between the stored subunit c and that in normal mitochondria. No other mitochondrial components are stored. Different proteins, sphingolipid activator proteins (SAPs or saposins) A and D, are stored in the infantile disease. Linkage studies have shown that different forms of ceroid-lipofuscinosis are coded for on different genes on different chromosomes. The genes for subunit c, its production, its insertion into mitochondria, and mitochondrial function are normal. This suggests that underlying the various forms of the disease is a family of lesions in the normal pathway of subunit c turnover, after its normal insertion into the ATP synthase complex. Antibodies to subunit c offer one way of mapping that pathway and detecting the sites of lesions. Specific antibodies have been raised against stored subunit c, using a liposomal adjuvant system which proved superior to classical adjuvants. These antibodies are also useful diagnostically, both in Western blotting and in immunocytochemistry.