Jonas Vikeså

Weaning Triggers a Maturation Step of Pancreatic β Cells

Because tissue regeneration deteriorates with age, it is generally assumed that the younger the animal, the better it compensates for tissue damage. We have examined the effect of young age on compensatory proliferation of pancreatic β cells in vivo. Surprisingly, β cells in suckling mice fail to enter the cell division cycle in response to a diabetogenic injury or increased glycolysis. The potential of β cells for compensatory proliferation is acquired following premature weaning to normal chow, but not to a diet mimicking maternal milk. In addition, weaning coincides with enhanced glucose-stimulated oxidative phosphorylation and insulin secretion from islets. Transcriptome analysis reveals that weaning increases the expression of genes involved in replication licensing, suggesting a mechanism for increased responsiveness to the mitogenic activity of high glucose. We propose that weaning triggers a discrete maturation step of β cells, elevating both the mitogenic and secretory response to glucose.

A Transgenic Mouse Marking Live Replicating Cells Reveals In Vivo Transcriptional Program of Proliferation

Most adult mammalian tissues are quiescent, with rare cell divisions serving to maintain homeostasis. At present, the isolation and study of replicating cells from their in vivo niche typically involves immunostaining for intracellular markers of proliferation, causing the loss of sensitive biological material. We describe a transgenic mouse strain, expressing a CyclinB1-GFP fusion reporter, that marks replicating cells in the S/G2/M phases of the cell cycle. Using flow cytometry, we isolate live replicating cells from the liver and compare their transcriptome to that of quiescent cells to reveal gene expression programs associated with cell proliferation in vivo. We find that replicating hepatocytes have reduced expression of genes characteristic of liver differentiation. This reporter system provides a powerful platform for gene expression and metabolic and functional studies of replicating cells in their in vivo niche.

ADAM12 redistributes and activates MMP-14, resulting in gelatin degradation, reduced apoptosis and increased tumor growth.

Summary Matrix metalloproteinases (MMPs), in particular MMP-2, MMP-9 and MMP-14, play a key role in various aspects of cancer pathology. Likewise, ADAMs (a disintegrin and metalloproteinases), including ADAM12, are upregulated in malignant tumors and contribute to the pathology of cancers. Here, we show that there is a positive correlation between MMP-14 and ADAM12 expression in human breast cancer. We demonstrated that in 293-VnR and human breast cancer cells expressing ADAM12 at the cell surface, endogenous MMP-14 was recruited to the cell surface, resulting in its activation. Subsequent to this activation, gelatin degradation was stimulated and tumor cell apoptosis was decreased, with reduced expression of the pro-apoptotic proteins BCL2L11 and BIK. The effect on gelatin degradation was abrogated by inhibition of the MMP-14 activity and appeared to be dependent on cell surface &agr;V&bgr;3 integrin localization, but neither the catalytic activity of ADAM12 nor the cytoplasmic tail of ADAM12 were required. The significance of ADAM12-induced activation of MMP-14 was underscored by a reduction in MMP-14-mediated gelatin degradation and abolition of apoptosis-protective effects by specific monoclonal antibodies against ADAM12. Furthermore, orthotopic implantation of ADAM12-expressing MCF7 cells in nude mice produced tumors with increased levels of activated MMP-14 and confirmed that ADAM12 protects tumor cells against apoptosis, leading to increased tumor progression. In conclusion, our data suggest that a ternary protein complex composed of ADAM12, &agr;V&bgr;3 integrin and MMP-14 at the tumor cell surface regulates the function of MMP-14. This interaction might point to a novel concept for the development of MMP-14-targeting drugs in treating cancer.

IMP3 RNP Safe Houses Prevent miRNA-Directed HMGA2 mRNA Decay in Cancer and Development

The IMP3 RNA-binding protein is associated with metastasis and poor outcome in human cancer. Using solid cancer transcriptome data, we found that IMP3 correlates with HMGA2 mRNA expression. Cytoplasmic IMP3 granules contain HMGA2, and IMP3 dose-dependently increases HMGA2 mRNA. HMGA2 is regulated by let-7, and let-7 antagomiRs make HMGA2 refractory to IMP3. Removal of let-7 target sites eliminates IMP3-dependent stabilization, and IMP3-containing bodies are depleted of Ago1-4 and miRNAs. The relationship between Hmga2 mRNA and IMPs also exists in the developing limb bud, where IMP1-deficient embryos show dose-dependent Hmga2 mRNA downregulation. Finally, IMP3 ribonucleoproteins (RNPs) contain other let-7 target mRNAs, including LIN28B, and a global gene set enrichment analysis demonstrates that miRNA-regulated transcripts in general are upregulated following IMP3 induction. We conclude that IMP3 RNPs may function as cytoplasmic safe houses and prevent miRNA-directed mRNA decay of oncogenes during tumor progression.

The dormant and the fully competent oocyte: comparing the transcriptome of human oocytes from primordial follicles and in metaphase II

Oocytes become enclosed in primordial follicles during fetal life and remain dormant there until activation followed by growth and meiotic resumption. Current knowledge about the molecular pathways involved in oogenesis is incomplete. This study identifies the specific transcriptome of the human oocyte in the quiescent state and at the pinnacle of maturity at ovulation. In silico bioinformatic comparisons were made between the transcriptome of human oocytes from dormant primordial follicles and that of human metaphase II (MII) oocytes and granulosa cells and unique gene expression profiles were identified as well as functional and pathway enrichments associated with the oocytes from the two developmental hallmarks. A total of 729 genes were highly enriched in oocytes from primodial follicles and 1456 genes were highly enriched in MII oocytes (>10-fold, P < 0.001) representing functional categories such as cell cycle regulation, DNA protection and epigenetics, with representative genes validated by qPCR analysis. Dominating canonical pathways in the oocytes from primordial follicles were androgen, estrogen receptor, glucocorticoid receptor and PI3K/AKT signaling (P < 0.001). In the MII, mitotic roles of polo-like kinases, estrogen receptor, JAK/Stat signaling (P < 0.001) and the ERK/MAPK (P < 0.01) signaling were enriched. Some of the highly differentially expressed genes were completely new in human reproduction (CDR1, TLC1A, UHRF2) while other genes [ABO, FOLR1 (folate receptor), CHRNA3 (nicotine receptor)] may relate to clinical observations as diverse as premature ovarian failure, folic acid deficiency and smoking affecting female fertility. The in silico analysis identified novel reproduction-associated genes and highlighted molecular mechanisms and pathways associated with the unique functions of the human oocyte in its two extremes during folliculogenesis. The data provides a fundamental basis for future functional studies in regulation of human oogenesis.

Characterization of miRNA Expression in Human Degenerative Lumbar Disks

Background data: microRNAs (miRNAs) are short ∼22 nucleotide RNA sequences that regulate messengerRNA translation. miRNAs have shown to play a role in synthesis of inflammatory mediators. Since inflammation play a role in intervertebral disk (IVD) degeneration, the objective was to isolate miRNA from human lumbar intervertebral disks and subsequently characterize the difference in miRNA expression between the annulus fibrosus (AF) and nucleus pulposus (NP). Methods: Fourteen patients undergoing anterior interbody fusion for degenerative disk disease of the lumbar spine were included. During surgery biopsies from the intervertebral disks were obtained and immediately placed in RNAlater. The RNAlater was decanted and the samples frozen at –80˚C until RNA extraction. This was performed using the Trizol method. Global miRNA expression analysis was performed using the Affymetrix GeneChip® miRNA array. Results: We developed a method allowing the extraction of miRNA from human intervertebral disks usually yielding 1–4 µg of total RNA pr. 100 mg of disk. Twenty-seven miRNAs had a higher expression in the AF and 10 had the highest expression in the NP. Among the top 15 signaling pathways most likely to be controlled by these miRNAs were the transforming growth factor β (TGFβ), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF) epidermal growth factor (EGF), and actin cytoskeletal pathway. Conclusion: We have demonstrated the presence of miRNA in the human IVD. The miRNA expression differs from muscle tissue and there are differences between the miRNA expressed in the NP and AF. The miRNAs identified control signaling pathways important for maintenance of the IVD. Future studies may determine the importance of miRNA in the development of IVD disease.

Promoter polymorphism -119C/G in MYG1 (C12orf10) gene is related to vitiligo susceptibility and Arg4Gln affects mitochondrial entrance of Myg1

BackgroundMYG1 (Melanocyte proliferating gene 1, also C12orf10 in human) is a ubiquitous nucleo-mitochondrial protein, involved in early developmental processes and in adult stress/illness conditions. We recently showed that MYG1 mRNA expression is elevated in the skin of vitiligo patients. Our aim was to examine nine known polymorphisms in the MYG1 gene, to investigate their functionality, and to study their association with vitiligo susceptibility.MethodsNine single nucleotide polymorphisms (SNPs) in the MYG1 locus were investigated by SNPlex assay and/or sequencing in vitiligo patients (n = 124) and controls (n = 325). MYG1 expression in skin biopsies was detected by quantitative-real time PCR (Q-RT-PCR) and polymorphisms were further analysed using luciferase and YFP reporters in the cell culture.ResultsControl subjects with -119G promoter allele (rs1465073) exhibited significantly higher MYG1 mRNA levels than controls with -119C allele (P = 0.01). Higher activity of -119G promoter was confirmed by luciferase assay. Single marker association analysis showed that the -119G allele was more frequent in vitiligo patients (47.1%) compared to controls (39.3%, P < 0.05, OR 1.37, 95%CI 1.02-1.85). Analysis based on the stage of progression of the vitiligo revealed that the increased frequency of -119G allele occurred prevalently in the group of patients with active vitiligo (n = 86) compared to the control group (48.2% versus 39.3%, P < 0.05; OR 1.44, 95%CI 1.02-2.03). Additionally, we showed that glutamine in the fourth position (in Arg4Gln polymorphism) completely eliminated mitochondrial entrance of YFP-tagged Myg1 protein in cell culture. The analysis of available EST, cDNA and genomic DNA sequences revealed that Myg1 4Gln allele is remarkably present in human populations but is never detected in homozygous state according to the HapMap database.ConclusionsOur study demonstrated that both MYG1 promoter polymorphism -119C/G and Arg4Gln polymorphism in the mitochondrial signal of Myg1 have a functional impact on the regulation of the MYG1 gene and promoter polymorphism (-119C/G) is related with suspectibility for actively progressing vitiligo.

Expression of histamine receptors in the human endolymphatic sac: the molecular rationale for betahistine use in Menieres disease

AbstractThe human endolymphatic sac (ES) is situated in a duplicature of the dura in the posterior cranial fossa and constitutes a part of the inner ear. The sac possesses immunological capacities and is responsible for a major part of the trans-epithelial ion transport occurring within the inner ear, via molecular mechanisms similar to that of the kidney collecting duct epithelia. Dysfunction of the trans-epithelial ion transport has been hypothesized as the reason for the endolymphatic hydrops occurring in Menieres diseases. Thus, candidate drug selection for medical treatment of Menieres disease has been based on a potential capability of improving trans-epithelial ion transport. However, recent human studies seems to rule out diuretic therapy and The Committee for Medicinal Products for Human Use redrew the recommendation for trimetazidine (Vastarel) treatment in the management of Meniere disease in 2012. This leaves betahistine (Betaserc) as the only drug for potential prevention of the incapacitating attacks of dizziness, tinnitus and hearing loss. However, the histamine receptors targeted by betahistine have never been demonstrated in the human ES. Accordingly, this study aims to investigate the expression of histamine receptors of the human ES epithelium and sub-epithelial stroma. Following sampling of human endolymphatic sac tissue during translabyrinthine surgery, the expression of histamine receptor genes was determined by cDNA microarray analysis. Results were subsequently verified by immuno-histochemistry. The combined results of microarrays and immuno-histochemistry showed expression of the histamine receptor HRH1 in the epithelial lining of the ES, whereas HRH3 was expressed exclusively in the sub-epithelial capillary network. Receptors HRH2 and -4 were not expressed. The present data provide the first direct evidence of a molecular rationale for betahistine treatment in Menieres disease. A potential betahistine effect in Menieres disease may primarily be through the H3-receptor antagonism, leading to inhibition of vestibular neuro-transmission and central vaso-dilation. The H1-receptor localization in the ES epithelium suggests an immuno-regulatory effect.

Gene expression in the human endolymphatic sac: the solute carrier molecules in endolymphatic fluid homeostasis.

Objectives/Hypothesis The purpose of the present study is to explore, demonstrate, and describe the expression of genes related to the solute carrier (SLC) molecules of ion transporters in the human endolymphatic sac. Study Design cDNA microarrays and immunohistochemistry were used for analyses of fresh human endolymphatic sac tissue samples. Methods Twelve tissue samples of the human endolymphatic sac were obtained during translabyrinthine surgery for vestibular schwannoma. Microarray technology was used to investigate tissue sample expression of solute carrier family genes, using adjacent dura mater as control. Immunohistochemistry was used for verification of translation of selected genes, as well as localization of the specific protein within the sac. Results An extensive representation of the SLC family genes were upregulated in the human endolymphatic sac, including SLC26a4 Pendrin, SLC4a1 sodium-bicarbonate transporter, SLC9a2 sodium-hydrogen transporter, SLC12a3 thiazide-sensitive Na-Cl transporter, and SLC34a2 sodium-phosphate transporter. Conclusions Several important ion transporters of the SLC family are expressed in the human endolymphatic sac, including Pendrin, the thiazide-sensitive Na-Cl transporter, and the Na-phosphate transporter SLC34a2. The data provide a new knowledge base considering the ion-dependent metabolic mechanisms maintaining inner ear homeostasis. More specifically, the results indicate a strong similarity with the ion transportation occurring in the kidney collecting ducts. In addition, the findings prompt a revision of the theories behind contemporary pharmacological treatment of Ménière’s disease and may broaden the understanding of the pathogenesis of BPPV.

Gene expression demonstrates an immunological capacity of the human endolymphatic sac

The purpose of the present study is to explore, demonstrate, and describe the expression of genes related to the innate immune system in the human endolymphatic sac. It is hypothesized that the endolymphatic sac has a significant immunological function in the human inner ear.