David Jelinek

The National Niemann–Pick C1 disease database: Report of clinical features and health problems

Niemann–Pick type C1 (NPC1) disease is an autosomal recessive disorder characterized clinically by neonatal jaundice, hepatosplenomegaly, vertical gaze palsy, ataxia, dystonia, and progressive neurodegeneration. The present study provides basic clinical and health information from the National Niemann–Pick C1 disease database that was obtained using a clinical questionnaire of 83 questions mailed to families affected by NPC1 disease living in the United States. The study was conducted over a 1‐year period, during which time parents/caregivers and physicians completed the clinical questionnaire. Sixty‐four percent (87/136) of the questionnaires were returned, with 53% and 47% representing male and female NPC1 patients, respectively. The average age of diagnosis for NPC1 disease was 10.4 years, with one‐half of patients being diagnosed before the age of 6.9 years. The average age of death for NPC1 disease was 16.2 years, with one‐half of patients dying before the age of 12.5 years. A common clinical symptom reported at birth was neonatal jaundice (52%), followed by enlargement of the spleen (36%) and liver (31%); ascites (19%) and neonatal hypotonia (6%) were much less frequent. With respect to developmental difficulties, the most common findings included clumsiness (87%), learning difficulties (87%), ataxia (83%), dysphagia (80%), and vertical gaze palsy (81%). Together, these findings confirm and extend previous reports investigating the clinical features associated with NPC1 disease.

The National Niemann-Pick Type C1 Disease Database: correlation of lipid profiles, mutations, and biochemical phenotypes

Niemann-Pick type C1 disease (NPC1) is an autosomal recessive lysosomal storage disorder characterized by neonatal jaundice, hepatosplenomegaly, and progressive neurodegeneration. The present study provides the lipid profiles, mutations, and corresponding associations with the biochemical phenotype obtained from NPC1 patients who participated in the National NPC1 Disease Database. Lipid profiles were obtained from 34 patients (39%) in the survey and demonstrated significantly reduced plasma LDL cholesterol (LDL-C) and increased plasma triglycerides in the majority of patients. Reduced plasma HDL cholesterol (HDL-C) was the most consistent lipoprotein abnormality found in male and female NPC1 patients across age groups and occurred independent of changes in plasma triglycerides. A subset of 19 patients for whom the biochemical severity of known NPC1 mutations could be correlated with their lipid profile showed a strong inverse correlation between plasma HDL-C and severity of the biochemical phenotype. Gene mutations were available for 52 patients (59%) in the survey, including 52 different mutations and five novel mutations (Y628C, P887L, I923V, A1151T, and 3741_3744delACTC). Together, these findings provide novel information regarding the plasma lipoprotein changes and mutations in NPC1 disease, and suggest plasma HDL-C represents a potential biomarker of NPC1 disease severity.

Characterization of liver disease and lipid metabolism in the Niemann-Pick C1 mouse.

Niemann‐Pick type C1 (NPC1) disease is an autosomal‐recessive cholesterol‐storage disorder characterized by liver dysfunction, hepatosplenomegaly, and progressive neurodegeneration. The NPC1 gene is expressed in every tissue of the body, with liver expressing the highest amounts of NPC1 mRNA and protein. A number of studies have now indicated that the NPC1 protein regulates the transport of cholesterol from late endosomes/lysosomes to other cellular compartments involved in maintaining intracellular cholesterol homeostasis. The present study characterizes liver disease and lipid metabolism in NPC1 mice at 35 days of age before the development of weight loss and neurological symptoms. At this age, homozygous affected (NPC1−/−) mice were characterized with mild hepatomegaly, an elevation of liver enzymes, and an accumulation of liver cholesterol approximately four times that measured in normal (NPC1+/+) mice. In contrast, heterozygous (NPC1+/−) mice were without hepatomegaly and an elevation of liver enzymes, but the livers had a significant accumulation of triacylglycerol. With respect to apolipoprotein and lipoprotein metabolism, the results indicated only minor alterations in NPC1−/− mouse serum. Finally, compared to NPC1+/+ mouse livers, the amount and processing of SREBP‐1 and ‐2 proteins were significantly increased in NPC1−/− mouse livers, suggesting a relative deficiency of cholesterol at the metabolically active pool of cholesterol located at the endoplasmic reticulum. The results from this study further support the hypothesis that an accumulation of lipoprotein‐derived cholesterol within late endosomes/lysosomes, in addition to altered intracellular cholesterol homeostasis, has a key role in the biochemical and cellular pathophysiology associated with NPC1 liver disease. J. Cell. Biochem. 101: 498–516, 2007.

Npc1 haploinsufficiency promotes weight gain and metabolic features associated with insulin resistance

A recent population-based genome-wide association study has revealed that the Niemann-Pick C1 (NPC1) gene is associated with early-onset and morbid adult obesity. Concurrently, our candidate gene-based mouse growth study performed using the BALB/cJ NPC1 mouse model (Npc1) with decreased Npc1 gene dosage independently supported these results by suggesting an Npc1 gene-diet interaction in relation to early-onset weight gain. To further investigate the Npc1 gene in relation to weight gain and metabolic features associated with insulin resistance, we interbred BALB/cJ Npc1(+/-) mice with wild-type C57BL/6J mice, the latter mouse strain commonly used to study aspects of diet-induced obesity and insulin resistance. This breeding produced a hybrid (BALB/cJ-C57BL/6J) Npc1(+/-) mouse model with increased susceptibility to weight gain and insulin resistance. The results from our study indicated that these Npc1(+/-) mice were susceptible to increased weight gain characterized by increased whole body and abdominal adiposity, adipocyte hypertrophy and hepatic steatosis in the absence of hyperphagia. Moreover, these Npc1(+/-) mice developed abnormal metabolic features characterized by impaired fasting glucose, glucose intolerance, hyperinsulinemia, hyperleptinemia and dyslipidemia marked by an increased concentration of cholesterol and triacylglycerol associated with low-density lipoprotein and high-density lipoprotein. The overall results are consistent with a unique Npc1 gene-diet interaction that promotes both weight gain and metabolic features associated with insulin resistance. Therefore, the NPC1 gene now represents a previously unrecognized gene involved in maintaining energy and metabolic homeostasis that will contribute to our understanding concerning the current global epidemic of obesity and type 2 diabetes mellitus.

The genetics of childhood obesity and interaction with dietary macronutrients

The genes contributing to childhood obesity are categorized into three different types based on distinct genetic and phenotypic characteristics. These types of childhood obesity are represented by rare monogenic forms of syndromic or non-syndromic childhood obesity, and common polygenic childhood obesity. In some cases, genetic susceptibility to these forms of childhood obesity may result from different variations of the same gene. Although the prevalence for rare monogenic forms of childhood obesity has not increased in recent times, the prevalence of common childhood obesity has increased in the United States and developing countries throughout the world during the past few decades. A number of recent genome-wide association studies and mouse model studies have established the identification of susceptibility genes contributing to common childhood obesity. Accumulating evidence suggests that this type of childhood obesity represents a complex metabolic disease resulting from an interaction with environmental factors, including dietary macronutrients. The objective of this article is to provide a review on the origins, mechanisms, and health consequences of obesity susceptibility genes and interaction with dietary macronutrients that predispose to childhood obesity. It is proposed that increased knowledge of these obesity susceptibility genes and interaction with dietary macronutrients will provide valuable insight for individual, family, and community preventative lifestyle intervention, and eventually targeted nutritional and medicinal therapies.

Decreased Npc1 gene dosage in mice is associated with weight gain.

A recent genome‐wide association study has determined that the Niemann‐Pick C1 (NPC1) gene is associated with early‐onset and morbid adult obesity. However, what effects of the nonsynonymous variation in NPC1 on protein function result in weight gain remains unknown. The NPC1 heterozygous mouse model (Npc1+/−), which expresses one‐half the normal amounts of functional Npc1 protein compared to the homozygous normal (Npc1+/+) mouse, was used to determine whether decreased Npc1 gene dosage was associated with weight gain when fed either a low‐fat (10% kcal fat) or high‐fat (45% kcal fat) diet beginning at 4 weeks of age until 20 weeks of age. The results indicated that Npc1+/− mice had significantly increased weight gain beginning at 13 weeks of age when fed a high‐fat diet, but not when fed a low‐fat diet, compared to the Npc1+/+ mice fed the same diet. With respect to mice fed a high‐fat diet, the Npc1+/− mice continued to have significantly increased weight gain to 30 weeks of age. At this age, the Npc1+/− mice were found to have increased liver and inguinal adipose weights compared to the Npc1+/+ mice. Therefore, decreased Npc1 gene dosage resulting in decreased Npc1 protein function, promoted weight gain in mice fed a high‐fat diet consistent with a gene–diet interaction.

A high-fat diet supplemented with fish oil improves metabolic features associated with type 2 diabetes.

OBJECTIVE The goal of this study was to investigate the effects of a high-fat diet supplemented with fish oil or olive oil, fed to C57BL/6J mice for an extended period, on metabolic features associated with type 2 diabetes. METHODS Mice were fed one of four diets for 30 wk: a low-fat diet, a high-fat diet supplemented with lard, a high-fat diet supplemented with fish oil, or a high-fat diet supplemented with olive oil. Phenotypic and metabolic analysis were determined at 15 and 25 to 30 wk, thereby providing comparative analysis for weight gain, energy consumption, fat distribution, glucose and insulin tolerance, and hepatic/plasma lipid analysis. RESULTS Mice fed a high-fat diet supplemented with fish oil had improved glucose tolerance after an extended period compared with mice fed a high-fat diet supplemented with lard. Moreover, mice fed a high-fat diet supplemented with fish oil had significantly decreased concentrations of liver cholesterol, cholesteryl ester, and triacylglycerol compared with mice fed a high-fat diet supplemented with either lard or olive oil. CONCLUSION Mice fed a high-fat diet supplemented with fish oil improved metabolic features associated with type 2 diabetes such as impaired glucose tolerance and hepatic steatosis.

Amelioration of enteric neuropathology in a mouse model of Niemann-Pick C by Npc1 expression in enteric glia.

Niemann‐Pick C (NPC) disease is an autosomal recessive, lethal, neurodegenerative disorder caused by mutations in NPC1. By using the glial fibrillary acidic protein (GFAP) promoter, we demonstrated previously that astrocyte‐specific expression of Npc1 decreased neuronal storage of cholesterol in Npc1−/− mice; reduced numbers of axonal spheroids; and produced less degeneration of neurons, reactive astrocytes, and loss of myelin tracts in the central nervous system. GFAP‐Npc1, Npc1−/− mice exhibited markedly enhanced survival, and death was not associated with the severe terminal weight loss observed in Npc1−/− mice. Intestinal transit is delayed in Npc1−/− mice but is normal in GFAP‐NPC1, Npc1−/− until late in the course of their disease. Because glia play an important role in the enteric nervous system, we studied morphology and cholesterol content of intestines from Npc1−/− mice and examined the effect of GFAP‐promoted restoration of Npc1 in enteric glia. Although the number of neurons was not altered, the total amount of cholesterol stored in the small intestine was decreased, as were the number of neurons with inclusions and the number of inclusions per neuron. We conclude that expression of Npc1 by enteric glial cells can ameliorate the enteric neuropathology, and we speculate that dysfunction of the enteric nervous system contributes to the retarded intestinal transit, weight loss, and demise of Npc1−/− mice.

The Niemann-Pick C1 Gene Is Downregulated in Livers of C57BL/6J Mice by Dietary Fatty Acids, but Not Dietary Cholesterol, through Feedback Inhibition of the SREBP Pathway

The Niemann-Pick C1 (NPC1) gene is associated with human obesity. Mouse models with decreased Npc1 gene dosage are susceptible to weight gain when fed a high-fat diet, but not a low-fat diet, consistent with an Npc1 gene-diet interaction. The objectives of this study were to define regulation of the Npc1 gene and to investigate the Npc1 gene-diet interaction responsible for weight gain. The experimental design involved feeding C57BL/6J male mice a low-fat diet (with 0.00, 0.10, or 1.00% cholesterol) or a high-fat diet (with 0.02% cholesterol) until 30 wk to determine regulation of the Npc1 gene in liver. The key results showed that the Npc1 gene was downregulated by dietary fatty acids (54%, P = 0.022), but not by dietary cholesterol, through feedback inhibition of the sterol regulatory element-binding protein (SREBP) pathway. However, the dietary fatty acids secondarily increased liver cholesterol, which also inhibits the SREBP pathway. Similarly, the Npc1 gene was downregulated in peritoneal fibroblasts isolated from C57BL/6J weanling male mice not exposed to the experimental diets and incubated in media supplemented with purified oleic acid (37%, P = 0.038) but not in media supplemented with purified cholesterol. These results are important because they suggest a novel mechanism for the interaction of fatty acids with the Npc1 gene to influence energy balance and to promote weight gain. Moreover, the responsiveness of the Npc1 gene to fatty acids is consistent with studies that suggest that the encoded NPC1 protein has a physiologic role in regulating both cholesterol and fatty acid metabolism.

The C57BL/6J Niemann-Pick C1 mouse model with decreased gene dosage has impaired glucose tolerance independent of body weight

The human Niemann-Pick C1 (NPC1) gene has been found to be associated with extreme (early-onset and morbid-adult) obesity and type 2 diabetes independent of body weight. We previously performed growth studies using BALB/cJ Npc1 normal (Npc1+/+) and Npc1 heterozygous (Npc1+/-) mice and determined that decreased Npc1 gene dosage interacts with a high-fat diet to promote weight gain and adiposity. The present study was performed using both BALB/cJ and C57BL/6J Npc1+/+ and Npc1+/- mice to determine if decreased Npc1 gene dosage predisposes to metabolic features associated with type 2 diabetes. The results indicated that C57BL/6J Npc1+/- mice, but not BALB/cJ Npc1+/- mice, have impaired glucose tolerance when fed a low-fat diet and independent of body weight. The results also suggest that an accumulation of liver free fatty acids and hepatic lipotoxicity marked by an elevation in the amount of plasma alanine aminotransferase (ALT) may be responsible for hepatic insulin resistance and impaired glucose tolerance. Finally, the peroxisome-proliferator activated receptor α (PPARα) and sterol regulatory element-binding protein-1 (SREBP-1) pathways known to have a central role in regulating free fatty acid metabolism were downregulated in the livers, but not in the adipose or muscle, of C57BL/6J Npc1+/- mice compared to C57BL/6J Npc1+/+ mice. Therefore, decreased Npc1 gene dosage among two different mouse strains interacts with undefined modifying genes to manifest disparate yet often related metabolic diseases.