Abstract
KPTN-related disorder is an autosomal recessive disorder associated with germline variants in KPTN (previously known as kaptin), a component of the mTOR regulatory complex KICSTOR. To gain ...further insights into the pathogenesis of KPTN-related disorder, we analysed mouse knockout and human stem cell KPTN loss-of-function models.
Kptn
−/− mice display many of the key KPTN-related disorder phenotypes, including brain overgrowth, behavioural abnormalities, and cognitive deficits. By assessment of affected individuals, we have identified widespread cognitive deficits (n = 6) and postnatal onset of brain overgrowth (n = 19). By analysing head size data from their parents (n = 24), we have identified a previously unrecognized KPTN dosage-sensitivity, resulting in increased head circumference in heterozygous carriers of pathogenic KPTN variants.
Molecular and structural analysis of Kptn−/− mice revealed pathological changes, including differences in brain size, shape and cell numbers primarily due to abnormal postnatal brain development. Both the mouse and differentiated induced pluripotent stem cell models of the disorder display transcriptional and biochemical evidence for altered mTOR pathway signalling, supporting the role of KPTN in regulating mTORC1.
By treatment in our KPTN mouse model, we found that the increased mTOR signalling downstream of KPTN is rapamycin sensitive, highlighting possible therapeutic avenues with currently available mTOR inhibitors. These findings place KPTN-related disorder in the broader group of mTORC1-related disorders affecting brain structure, cognitive function and network integrity.
Levitin et al. model KPTN-related disorder in knockout mice and in human cells. Consistent with findings in patients, the mouse model shows cognitive and behavioural changes, as well as significant brain overgrowth. Reversible mTOR pathway disruption is evident in both models, suggesting therapeutic potential of mTOR inhibitors.
The transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator-1β (PGC-1β) has been implicated in important metabolic processes. A mouse lacking PGC-1β (PGC1βKO) was ...generated and phenotyped using physiological, molecular, and bioinformatic approaches. PGC1βKO mice are generally viable and metabolically healthy. Using systems biology, we identified a general defect in the expression of genes involved in mitochondrial function and, specifically, the electron transport chain. This defect correlated with reduced mitochondrial volume fraction in soleus muscle and heart, but not brown adipose tissue (BAT). Under ambient temperature conditions, PGC-1β ablation was partially compensated by up-regulation of PGC-1α in BAT and white adipose tissue (WAT) that lead to increased thermogenesis, reduced body weight, and reduced fat mass. Despite their decreased fat mass, PGC1βKO mice had hypertrophic adipocytes in WAT. The thermogenic role of PGC-1β was identified in thermoneutral and cold-adapted conditions by inadequate responses to norepinephrine injection. Furthermore, PGC1βKO hearts showed a blunted chronotropic response to dobutamine stimulation, and isolated soleus muscle fibres from PGC1βKO mice have impaired mitochondrial function. Lack of PGC-1β also impaired hepatic lipid metabolism in response to acute high fat dietary loads, resulting in hepatic steatosis and reduced lipoprotein-associated triglyceride and cholesterol content. Altogether, our data suggest that PGC-1β plays a general role in controlling basal mitochondrial function and also participates in tissue-specific adaptive responses during metabolic stress.
The authors conduct an in-depth analysis of a PGC-1β knockout mouse; these animals posses specific defects in basal mitochondrial function and adaptation to metabolic stress.
Miller-Dieker syndrome is caused by a multiple gene deletion, including PAFAH1B1 and YWHAE. Although deletion of PAFAH1B1 causes lissencephaly unambiguously, deletion of YWHAE alone has not clearly ...been linked to a human disorder.
Cases with YWHAE variants were collected through international data sharing networks. To address the specific impact of YWHAE loss of function, we phenotyped a mouse knockout of Ywhae.
We report a series of 10 individuals with heterozygous loss-of-function YWHAE variants (3 single-nucleotide variants and 7 deletions <1 Mb encompassing YWHAE but not PAFAH1B1), including 8 new cases and 2 follow-ups, added with 5 cases (copy number variants) from literature review. Although, until now, only 1 intragenic deletion has been described in YWHAE, we report 4 new variants specifically in YWHAE (3 splice variants and 1 intragenic deletion). The most frequent manifestations are developmental delay, delayed speech, seizures, and brain malformations, including corpus callosum hypoplasia, delayed myelination, and ventricular dilatation. Individuals with variants affecting YWHAE alone have milder features than those with larger deletions. Neuroanatomical studies in Ywhae−/− mice revealed brain structural defects, including thin cerebral cortex, corpus callosum dysgenesis, and hydrocephalus paralleling those seen in humans.
This study further demonstrates that YWHAE loss-of-function variants cause a neurodevelopmental disease with brain abnormalities.
Myosin 10 is involved in murine pigmentation Liakath‐Ali, Kifayathullah; Vancollie, Valerie E.; Sequeira, Inês ...
Experimental dermatology,
April 2019, Letnik:
28, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Myosins are molecular motors that are well known for their role in cell movement and contractile functions. Although extensively studied in muscle physiology, little is known about the function of ...myosins in mammalian skin. As part of the Sanger Institute Mouse Genetics Project, we have identified a role for Myo10 in pigmentation, with a phenotype unlike those of Myo5a or Myo7a. Adult mice homozygous for a disrupted Myo10 allele on a C57BL/6N background displayed a high degree of penetrance for white patches on their abdomen and dorsal surface. Forepaw syndactyly and hind paw syndactyly were also observed in these mice. Tail epidermal wholemounts showed a complete lack of melanocytes in the hair follicles and interfollicular epidermis. Myo10 has previously been implicated in human pigmentation. Our current study reveals involvement of Myo10 in murine skin pigmentation.
Genome-wide association studies (GWAS) have detected association between variants in or near the
(
) locus and metabolic traits, including central obesity, fatty liver and waist-to-hip ratio.
is also ...known to be upregulated in the adipose tissue of obese patients. However, the physiological role of
is not understood. To investigate the function of
we investigated the phenotype of the
homozygous mouse. Body composition was unaltered in
knockout mice as assessed by dual-energy X-ray absorptiometry (DEXA) scanning, both on normal chow and on a high-fat diet. Adipose tissue distribution between visceral and subcutaneous fat depots was unaltered, with no change in adipocyte cell size. The response to both insulin and glucose dosing was normal in
homozygous mice, with normal fasting blood glucose concentrations. RNAseq analysis of liver, muscle and adipose tissue confirmed that
expression was ablated with minimal additional changes in gene expression. These results suggest that
is dispensable for normal mouse metabolic physiology and that despite having been maintained through evolution
is not an essential gene, suggesting possible functional redundancy. Further studies will be required to clarify its physiological role.
Objective: Adiponectin mRNA expression in isolated subcutaneous and omental adipocytes was examined across a wide range of adiposity to determine whether adiponectin synthesis is impaired in these ...adipose tissue depots in obese humans. Tumor necrosis factor (TNF)α and dexamethasone were tested for inhibitory effects on adiponectin release from human adipocytes in vitro.
Research Methods and Procedures: Adipocytes were isolated by collagenase digestion of abdominal adipose tissue obtained from subjects undergoing surgical procedures or outpatient needle biopsy. Adiponectin and leptin mRNA were quantitated by real‐time reverse transcriptase‐polymerase chain reaction. Adiponectin and leptin secretion from isolated adipocytes treated with dexamethasone or TNFα were determined by radioimmunoassay.
Results: There was a significant negative correlation between adiponectin gene expression and BMI in subcutaneous adipocytes from 32 women (r = 0.420; p = 0.02). Adiponectin mRNA was also significantly correlated with serum adiponectin (r = 0.44; p = 0.03; n = 25). There was no correlation between adiponectin mRNA expression and BMI in omental adipocytes from 29 women. Leptin mRNA was significantly and positively correlated (r = 0.484; p = 0.01) with BMI in the same omental adipocyte mRNA preparations. In subcutaneous adipocytes from lean subjects, TNFα inhibited adiponectin release by 7.4 ± 1.2% (n = 9, p < 0.05) but had no effect on adiponectin release from subcutaneous or omental adipocytes from obese subjects. Dexamethasone significantly inhibited adiponectin release with 24 hours of treatment.
Discussion: The data suggest that reduced adiponectin synthesis in subcutaneous adipocytes contributes to lower serum adiponectin levels in obesity and that glucocorticoids regulate adiponectin gene expression in human adipocytes. TNFα does not seem to directly inhibit adiponectin synthesis in human adipocytes.
Nonalcoholic steatohepatitis (NASH) is a common feature of the metabolic syndrome and toxic reactions to pharmacological drugs. Tamoxifen, (TMX) a widely used anti-breast cancer drug, can induce NASH ...and changes in plasma cholesterol levels through mechanisms that are unclear. We studied primary actions of TMX using a short-term treatment (5 days) that induces microvesicular hepatic steatosis and marked hypercholesterolemia in male rats. Using a combined approach of gene expression profiling and NMR-based metabolite analysis, we found that TMX-treated livers have increased saturated fatty acid content despite changes in gene expression, indicating decreased de novo lipogenesis and increased fatty acid oxidation. Our results show that TMX predominantly down-regulates FAS expression and activity as indicated by the accumulation of malonyl-CoA, a known inhibitor of mitochondrial {szligbeta}-oxidation. In the face of a continued supply of exogenous free fatty acids, the blockade of fatty acid oxidation produced by elevated malonyl-CoA is likely to be the major factor leading to steatosis. Use of a combination of metabolomic and transcriptomic analysis has allowed us to identify mechanisms underlying important metabolic side effects of a widely prescribed drug. Given the broader importance of hepatic steatosis, the novel molecular mechanism revealed in this study should be examined in other forms of steatosis and nonalcoholic steatohepatitis.--Lelliott, C. J., López, M., Curtis, R. K., Parker, N., Laudes, M., Yeo, G., Jimenez-Liñan, M., Grosse, J., Saha, A. K., Wiggins, D., Hauton, D., Brand, M. D., O'Rahilly, S., Griffin, J. L., Gibbons, G. F., Vidal-Puig, A. Transcript and metabolite analysis of the effects of tamoxifen in rat liver reveals inhibition of fatty acid synthesis in the presence of hepatic steatosis.
Peroxisome proliferator‐activated receptor gamma‐coactivator‐1 alpha (PGC1a) is involved in energy and lipid metabolism, and its loss leads to neurodegenerative changes in the striatum. Here we ...performed lipidomic analysis on brain extracts from PGC1a mutant and wild‐type mice. We found increased phosphatidylcholine and decreased ceramides in the brain of PGC1a‐deficient mice. An analysis of lipid raft fractions revealed increased ceramide, glucocylceramides and GM1 ganglioside in the PGC1a mutants. In the cerebellum, we observed a decrease in proteins associated with myelination, but were unable to detect any morphological abnormalities in compact myelin formation in PGC1a mutants compared with wild‐type mice. Although PGC1a is involved in lipid biosynthesis, we concluded that altered lipid composition in the PGC1a mutant did not directly affect central nervous system myelin morphology.
Peroxisome proliferator‐activated receptor gamma‐coactivator‐1 alpha (PGC1a) is involved in energy and lipid metabolism, and its loss leads to neurodegeneration. Ablation of PGC1a increased phosphatidylcholine and decreased ceramides in the brain. An analysis of lipid raft fractions revealed increased ceramide, glucocylceramides and GM1 ganglioside in the PGC1a mutants. We suggest that PGC1a coactivator coordinates brain age‐dependent sphingolipid metabolism and oligodendrocyte differentiation.
PDF
