Patsy M. Nishina

Hyperproinsulinaemia in obese fat/fat mice associated with a carboxypeptidase E mutation which reduces enzyme activity.

Mice homozygous for the fat mutation develop obesity and hyperglycaemia that can be suppressed by treatment with exogenous insulin. The fat mutation maps to mouse chromosome 8, very close to the gene for carboxypeptidase E (Cpe), which encodes an enzyme (CPE) that processes prohormone intermediates such as proinsulfn. We now demonstrate a defect in proinsulin processing associated with the virtual absence of CPE activity in extracts of fat/fat pancreatic islets and pituitaries. A single Ser202Pro mutation distinguishes the mutant Cpe allele, and abolishes enzymatic activity in vitro. Thus, the fat mutation represents the first demonstration of an obesity–diabetes syndrome elicited by a genetic defect in a prohormone processing pathway.

Mutations in ALMS1 cause obesity, type 2 diabetes and neurosensory degeneration in Alström syndrome.

Alström syndrome is a homogeneous autosomal recessive disorder that is characterized by childhood obesity associated with hyperinsulinemia, chronic hyperglycemia and neurosensory deficits. The gene involved in Alström syndrome probably interacts with genetic modifiers, as subsets of affected individuals present with additional features such as dilated cardiomyopathy, hepatic dysfunction, hypothyroidism, male hypogonadism, short stature and mild to moderate developmental delay, and with secondary complications normally associated with type 2 diabetes, such as hyperlipidemia and atherosclerosis. Our detection of an uncharacterized transcript, KIAA0328, led us to identify the gene ALMS1, which contains sequence variations, including four frameshift mutations and two nonsense mutations, that segregate with Alström syndrome in six unrelated families. ALMS1 is ubiquitously expressed at low levels and does not share significant sequence homology with other genes reported so far. The identification of ALMS1 provides an entry point into a new pathway leading toward the understanding of both Alström syndrome and the common diseases that characterize it.

Atherosclerosis and plasma and liver lipids in nine inbred strains of mice.

Nine inbred strains of mice, which are progenitors of recombinant inbred sets, were evaluated for aortic lesion formation and plasma and liver lipid levels. This survey was done to determine if a semi-synthetic high-fat diet could elicit the same extent of diet-induced atherosclerosis as that observed in mice fed a natural ingredient highfat diet and to discover strain-specific plasma and liver lipid variants for future genetic characterization. Evaluation of aortic lesions after 18 wk of diet consumption showed that strains C57BL/6J, C57L/J, SWR/J and SM/J were susceptible to atherosclerosis and that A/J, AKR/J, C3H/HeJ, DBA/2J and SJL/J were relatively resistant. High-density lipoprotein cholesterol (HDL-C) levels were negatively correlated to lesion formation. Susceptible strains had decreased HDL-C levels when switched from chow to the semi-synthetic high-fat, high cholesterol diet, whereas resistant strains either showed no change or a slight increase in HDL-C levels. The exception to this pattern was found in SM mice, which were susceptible to aortic lesion formation but maintained the same HDL-C level on both chow and high-fat diets. HDL size differed among the strains, and levels of plasma apolipoprotein A-I and A-II correlated with HDL-C levels. Liver damage was not correlated to HDL-C levels or to susceptibility to atherosclerosis. Mice from strain A, which are resistant to atherosclerosis, had evidence of liver damage as observed by elevated levels of plasma alanine aminotransferase activity, by liver histology, by increased liver weight and by exceptionally high hepatic cholesterol content. For all strains, the levels of liver cholesterol and triglycerides were inversely correlated with each other; phospholipids did not vary greatly among strains. No remarkable differences in hepatic fatty acid profile were noted among the strains fed the atherogenic diet, but the fatty acid profile did differ considerably from that found in the diet itself.

Atherosclerosis in Genetically Obese Mice: The Mutants Obese, Diabetes, Fat, Tubby, and Lethal Yellow

Mice with five different mutations conferring an obese or diabetic phenotype were evaluated for fatty streak lesions after consuming an atherogenic diet containing 15% fat and 1.25% cholesterol (wt/wt) for 14 weeks. The five mutations, fat, obese, tubby, diabetes, and lethal yellow, are maintained as congenic strains with C57BL/6J (B6) or C57BL/KsJ (BKs) as genetic backgrounds. None of the mutants exhibited accelerated fatty streak lesion formation; the mutant fat had aortic lesions comparable in size to those of its control strain, and the mutants obese, diabetes, tubby, and lethal yellow had significantly reduced lesion area in comparison to controls. Although B6 and BKs are closely related strains, we observed that the BKs strain was more prone to early-stage atherogenesis. Fatty streak lesion area was twice as large in BKs mice than those found in B6 mice; likewise, in comparison, the mutants obese and diabetes had larger lesions if they were carried as congenic strains in the BKs rather than the B6 genetic background. Plasma triglycerides, total cholesterol, high-density lipoprotein cholesterol (HDL-C), and combined low-density and very-low-density lipoprotein cholesterol (LDL-C and VLDL) levels were also measured in the mice. Lipid profiles differed among the mutant mice, but in general, elevations in plasma total cholesterol, triglycerides, and HDL-C were observed. Whereas the hypertriglyceridemia and hypercholesterolemia are consistent with an atherogenic lipid profile, HDL-C levels, which are normally decreased in individuals with non-insulin-dependent diabetes mellitus, were increased in the mouse mutants.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of plasma lipids in genetically obese mice: The mutants obese, diabetes, fat, tubby, and lethal yellow

Plasma lipid levels were measured in control strains C57BL/6J (B6) and C57BL/KsJ (BKs) and in the mutants obese (ob), diabetes (db), fat (fat), tubby (tub), and lethal yellow (Ay), which are considered models of non-insulin-dependent diabetes mellitus (NIDDM), to determine if perturbations in plasma lipids were similar to those observed in the obese or diabetic human population. Compared with control mice, obese, diabetes, tubby, and lethal yellow mice had triglyceride levels that were elevated 1.5-fold to twofold, but fat mice had triglyceride levels similar to those of controls. Elevated plasma cholesterol levels, which were also observed in most mutant mice, were mainly due to an increase in high-density lipoprotein cholesterol (HDL-C). The degree of hypercholesterolemia appeared to be related to the age of onset and severity of the obesity and diabetes phenotype, with the greatest elevations occurring in obese and diabetes, milder elevations in fat mice of both sexes, male tubby, and male yellow mice, and no apparent changes in female tubby or lethal yellow mice. Plasma HDL-C and glucose levels and body weight in B6-db/db mice and their normal littermates were measured at intervals between 2 and 12 weeks of age to determine when the changes in cholesterol occurred in relationship to hyperglycemia and obesity. An elevation in HDL-C in B6-db/db mice was apparent by 3 weeks of age, a time concurrent with the elevation in blood glucose but before any weight differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Microtubule-associated protein 1A is a modifier of tubby hearing (moth1).

Once a mutation in the gene tub was identified as the cause of obesity, retinal degeneration and hearing loss in tubby mice, it became increasingly evident that the members of the tub gene family (tulps) influence maintenance and function of the neuronal cell lineage. Suggested molecular functions of tubby-like proteins include roles in vesicular trafficking, mediation of insulin signaling and gene transcription. The mechanisms through which tub functions in neurons, however, have yet to be elucidated. Here we report the positional cloning of an auditory quantitative trait locus (QTL), the modifier of tubby hearing 1 gene (moth1), whose wildtype alleles from strains AKR/J, CAST/Ei and 129P2/OlaHsd protect tubby mice from hearing loss. Through a transgenic rescue experiment, we verified that sequence polymorphisms in the neuron-specific microtubule-associated protein 1a gene (Mtap1a) observed in the susceptible strain C57BL/6J (B6) are crucial for the hearing-loss phenotype. We also show that these polymorphisms change the binding efficiency of MTAP1A to postsynaptic density molecule 95 (PSD95), a core component in the cytoarchitecture of synapses. This indicates that at least some of the observed polymorphisms are functionally important and that the hearing loss in C57BL/6J-tub/tub (B6-tub/tub) mice may be caused by impaired protein interactions involving MTAP1A. We therefore propose that tub may be associated with synaptic function in neuronal cells.

Aberrant actin cytoskeleton leads to accelerated proliferation of corneal epithelial cells in mice deficient for destrin (actin depolymerizing factor)

Corneal disease is the most common cause of bilateral blindness in the world. Visual loss in this condition is often due to changes in morphology and function of the corneal epithelial surface. Corneal disease-1 (corn1) and corn1(2J) are spontaneous mouse mutants that develop irregular thickening of the corneal epithelium, similar to that observed in human corneal surface disease. These autosomal-recessive mutations cause an increase in the rate of proliferation of the corneal epithelial cells. Here, we report that the phenotypes in both mutants are caused by mutations within the destrin gene (also known as actin-depolymerizing factor). By positional cloning, we identified a deletion encompassing the entire coding sequence of the destrin gene in corn1 mice, and a point mutation (Pro106Ser) in the coding sequence of destrin in corn1(2J) mice. In situ analysis showed that destrin is highly expressed in the corneal epithelium. Consistent with the cellular roles for destrin, an essential regulator of actin filament turnover that acts by severing and enhancing depolymerization of actin filament, we observed that the corn1 mutations increased the content of filamentous actin in corneal epithelial cells. Our results suggest an in vivo connection between remodeling of the actin cytoskeleton and the control of cell proliferation, and a new pathway through which an aberrant actin cytoskeleton can cause epithelial hyperproliferation.

GPR179 is required for depolarizing bipolar cell function and is mutated in autosomal-recessive complete congenital stationary night blindness

Complete congenital stationary night blindness (cCSNB) is a clinically and genetically heterogeneous group of retinal disorders characterized by nonprogressive impairment of night vision, absence of the electroretinogram (ERG) b-wave, and variable degrees of involvement of other visual functions. We report here that mutations in GPR179, encoding an orphan G protein receptor, underlie a form of autosomal-recessive cCSNB. The Gpr179(nob5/nob5) mouse model was initially discovered by the absence of the ERG b-wave, a component that reflects depolarizing bipolar cell (DBC) function. We performed genetic mapping, followed by next-generation sequencing of the critical region and detected a large transposon-like DNA insertion in Gpr179. The involvement of GPR179 in DBC function was confirmed in zebrafish and humans. Functional knockdown of gpr179 in zebrafish led to a marked reduction in the amplitude of the ERG b-wave. Candidate gene analysis of GPR179 in DNA extracted from patients with cCSNB identified GPR179-inactivating mutations in two patients. We developed an antibody against mouse GPR179, which robustly labeled DBC dendritic terminals in wild-type mice. This labeling colocalized with the expression of GRM6 and was absent in Gpr179(nob5/nob5) mutant mice. Our results demonstrate that GPR179 plays a critical role in DBC signal transduction and expands our understanding of the mechanisms that mediate normal rod vision.

Genealogy, natural history, and phenotype of Alstrom syndrome in a large Acadian kindred and three additional families.

We describe a large Acadian kindred including 8 Alstrom Syndrome (AS) patients, with an age range of 4 to 26 at the time of clinical assessment. The affected subjects come from 5 nuclear families within this kindred. The phenotype includes early childhood retinopathy, progressive sensorineural hearing loss, truncal obesity, and acanthosis nigricans. In addition, hyperinsulinemia and hypertriglyceridemia with normal cholesterol levels were observed in most affected individuals tested. Non-insulin dependent diabetes mellitus and growth retardation appear to be age-related manifestations that occur post-adolescence. Younger affected children are not overtly hyperglycemic and are normal or above average height for age. Although the AS patients in kindred 1 presumably carry the same mutation, many manifestations of the disease are variable. For example, of the 8 children in the Acadian kindred, 4 have scoliosis, 2 have had infantile cardiomyopathy, 2 are hypothyroid, 1 has had hepatic dysfunction and is hypertensive, and 4 have developed asthma. Seven subjects described in this kindred exhibit developmental delay. One additional manifestation not described widely in the literature, advanced bone age, was observed in all subjects tested. The clinical data from this large Acadian kindred, together with information obtained from 4 additional AS patients in 3 unrelated kindreds, confirm and extend clinical observations previously described. In addition, the Acadian kindred with multiple affected individuals, probably arising from a common founder, should allow for identification of the chromosomal localization of a gene causing AS.

Ocular abnormalities in Largemyd and Largevls mice, spontaneous models for muscle, eye, and brain diseases

Here we demonstrate previously unreported ocular defects in mice homozygous for a new allele of the Large gene, veils, and for Large(myd) mice. Clinically, vitreal fibroplasia and retinal vessel tortuosity and fluorescein leakage are observed. These vascular defects may be due to the extreme disorganization of the astrocytic template on which endothelial cells migrate in the retina. Abnormal electroretinograms recorded from Large(vls) or Large(myd) mice are accompanied by disorganization of the outer plexiform layer (OPL) with a dramatic reduction in the number of synaptic complexes. In both mutants, the internal limiting membrane (ILM) is disrupted with ectopic cells in the vitreous. Interestingly, while all components of the dystrophin glycoprotein complex are present at reduced levels in the OPL, they were absent in the ILM of affected mice. Finally, hypoglycosylation of alpha-dystroglycan previously implicated in muscle and brain defects is also observed in the retina and may contribute to the ocular abnormalities.