Objectives: Metabolomics is a new approach to precisely phenotype individuals and identify potentially novel biomarkers. Although GC- and LC-MS/MS based metabolomics has been established to determine the metabolome in plants, these techniques have not yet been evaluated in human plasma. We therefore aimed to analyze the reproducibility of measurements under various conditions.
Adiponectin has recently been reported to generate a negative energy balance by increasing energy expenditure. However, it is unclear whether such effects require the presence and direct action of the adiponectin protein in the central nervous system. In this study, neither radiolabeled nonglycosylated nor glycosylated globular adiponectin crossed the blood-brain barrier (BBB) in mice. In addition, adiponectin was not detectable in human cerebrospinal fluid using various established methods. Using murine cerebral microvessels, we demonstrated expression of adiponectin receptors, which are upregulated during fasting, in brain endothelium. Interestingly, treatment with adiponectin reduced secretion of the centrally active interleukin-6 from brain endothelial cells, a phenomenon that was paralleled by a similar trend of other proinflammatory cytokines. In summary, our data suggest that direct effects of endogenous adiponectin on central nervous system pathways are unlikely to exist. However, the identification of adiponectin receptors on brain endothelial cells and the finding of a modified secretion pattern of centrally active substances from BBB cells provides an alternate explanation as to how adiponectin may evoke effects on energy metabolism.
Cohen syndrome is a rare autosomal recessive disorder with a complex phenotype including psychomotor retardation, microcephaly, obesity with slender extremities, joint laxity, progressive chorioretinal dystrophy/myopia, intermittent isolated neutropenia, a cheerful disposition, and characteristic facial features. The COH1 gene, which contains 62 exons, is so far the only gene known to be associated with Cohen syndrome. Point mutations, deletions and duplications have been described in this gene. Oligonucleotide arrays have reached a resolution which allows the detection of intragenic deletions and duplications, especially in large genes such as COH1.High density oligonucleotide array data from patients with unexplained mental retardation (n=1523) and normal controls (n=1612) were analysed for copy number variation (CNV) changes. Intragenic heterozygous deletions in the COH1 gene were detected in three patients but no such changes were detected in the controls. Subsequent sequencing of the COH1 gene revealed point mutations in the second allele in all three patients analysed.Genome-wide CNV screening with high density arrays provides a tool to detect intragenic deletions in the COH1 gene. This report presents an example of how microarrays can be used to identify autosomal recessive syndromes and to extend the phenotypic and mutational spectrum of recessive disorders.
Objectives: Several studies have demonstrated that chronic exposure of pancreatic beta-cells or islets to supraphysiological glucose concentrations results in loss of the glucose responsiveness of the insulin promoter and reduced insulin expression. We aimed to investigate the signalling pathways involved in this process in more detail using the insulinoma cell line INS-1.
The authors observed a patient with a cryptic subtelomeric de novo balanced translocation 46,XY.ish t(11;20)(p15.4;q13.2) presenting with severe mental retardation, muscular hypotonia, seizures, bilateral sensorineural hearing loss, submucous cleft palate, persistent ductus Botalli, unilateral cystic kidney dysplasia and frequent infections.
Methods and Results
Fluorescence in situ hybridisation mapping and sequencing of the translocation breakpoints showed that no known genes are disrupted at 20q13.2 and that ST5 (suppression of tumorigenicity 5; MIM 140750) is disrupted on 11p15.4. By quantitative PCR from different human tissues, the authors found ST5 to be relatively evenly expressed in fetal tissues. ST5 expression was more pronounced in adult brain, kidney and muscle than in the corresponding fetal tissues, whereas expression in other tissues was generally lower than in the fetal tissue. Using RNA in situ hybridisation in mouse, the authors found that St5 is expressed in the frontal cortex during embryonic development. In adult mouse brain, expression of St5 was especially high in the hippocampal area and cerebellum.
Conclusion
Hence, the authors suppose that ST5 plays an important role in central nervous system development probably due to disturbance of DENN-domain-mediated vesicle formation and neurotransmitter trafficking. Thus, these findings implicate ST5 in the aetiology of mental retardation, seizures and multiple congenital anomalies.
Abstract As models for β-cell metabolism, rat islets are, to some extent, a, heterogeneous cell population stressed by the islet isolation procedure, whereas rat-derived clonal β-cells exhibit a tumor-like phenotype. To describe to what extent either of these models reflect normal cellular metabolism, we compared metabolite profiles and gene expression in rat islets and the INS-1 832/13 line, a widely used clonal β-cell model. We found that insulin secretion and metabolic regulation provoked by glucose were qualitatively similar in these β-cell models. However, rat islets exhibited a more pronounced glucose-provoked increase of glutamate, glycerol-3-phosphate, succinate, and lactate levels, whereas INS-1 832/13 cells showed a higher glucose-elicited increase in glucose-6-phosphate, alanine, isocitrate, and α-ketoglutarate levels. Glucose induced a decrease in levels of γ-aminobutyrate (GABA) and aspartate in rat islets and INS-1 832/13 cells, respectively. Genes with cellular functions related to proliferation and the cell cycle were more highly expressed in the INS-1 832/13 cells. Most metabolic pathways that were differentially expressed included GABA metabolism, in line with altered glucose responsiveness of GABA. Also, lactate dehydrogenase A, which is normally expressed at low levels in mature β-cells, was more abundant in rat islets than in INS-1 832/13 cells, confirming the finding of elevated glucose-provoked lactate production in the rat islets. Overall, our results suggest that metabolism in rat islets and INS-1 832/13 cells is qualitatively similar, albeit with quantitative differences. Differences may be accounted for by cellular heterogeneity of islets and proliferation of the INS-1 832/13 cells.
We have previously identified transcription factor B1 mitochondrial (TFB1M) as a type 2 diabetes (T2D) risk gene, using human and mouse genetics. To further understand the function of TFB1M and how it is associated with T2D, we created a β-cell-specific knockout of Tfb1m, which gradually developed diabetes. Prior to the onset of diabetes, β-Tfb1m−/− mice exhibited retarded glucose clearance owing to impaired insulin secretion. β-Tfb1m−/− islets released less insulin in response to fuels, contained less insulin and secretory granules and displayed reduced β-cell mass. Moreover, mitochondria in Tfb1m-deficient β-cells were more abundant with disrupted architecture. TFB1M is known to control mitochondrial protein translation by adenine dimethylation of 12S ribosomal RNA (rRNA). Here, we found that the levels of TFB1M and mitochondrial-encoded proteins, mitochondrial 12S rRNA methylation, ATP production and oxygen consumption were reduced in β-Tfb1m−/− islets. Furthermore, the levels of reactive oxygen species (ROS) in response to cellular stress were increased whereas induction of defense mechanisms was attenuated. We also show increased apoptosis and necrosis as well as infiltration of macrophages and CD4+ cells in the islets. Taken together, our findings demonstrate that Tfb1m-deficiency in β-cells caused mitochondrial dysfunction and subsequently diabetes owing to combined loss of β-cell function and mass. These observations reflect pathogenetic processes in human islets: using RNA sequencing, we found that the TFB1M risk variant exhibited a negative gene-dosage effect on islet TFB1M mRNA levels, as well as insulin secretion. Our findings highlight the role of mitochondrial dysfunction in impairments of β-cell function and mass, the hallmarks of T2D.
In this issue of Journal of Endocrinology , Dr Han and colleagues report a protective effect of the glutamate dehydrogenase activator 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) under diabetes-like conditions that impair β-cell function in both a pancreatic β-cell line and db/db mice. Based on these observations, the authors suggest that BCH could serve as a novel treatment modality in type 2 diabetes. The present commentary discusses the importance of the findings. Some additional questions are raised, which may be addressed in future investigations, as there is some concern regarding the BCH treatment of β-cell failure.
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