Depletion of plasma thymidine results in growth retardation and mitochondrial myopathy in mice overexpressing human thymidine phosphorylase.

Plasma thymidine levels in rodents are higher than in other mammals including humans, possibly due to a different pattern and lower level of thymidine phosphorylase expression. Here, we generated a novel knock-in (KI) mouse line with high systemic expression of human thymidine phosphorylase to investigate this difference in nucleotide metabolism in rodents. The KI mice showed growth retardation around weaning and died by 4 weeks of age with a decrease in plasma thymidine level compared with the litter-control WT mice. These phenotypes were completely or partially rescued by administration of the thymidine phosphorylase inhibitor 5-chloro-6-(2-iminopyrrolidin-1-yl) methyl-2,4(1H,3H)-pyrimidinedione hydrochloride or thymidine, respectively. Interestingly, when thymidine phosphorylase inhibitor administration was discontinued in adult animals, KI mice showed deteriorated grip strength and locomotor activity, decreased bodyweight, and subsequent hind-limb paralysis. Upon histological analyses, we observed axonal degeneration in the spinal cord, muscular atrophy with morphologically abnormal mitochondria in quadriceps, retinal degeneration, and abnormality in the exocrine pancreas. Moreover, we detected mitochondrial DNA depletion in multiple tissues of KI mice. These results indicate that the KI mouse represents a new animal model for mitochondrial diseases and should be applicable for the study of differences in nucleotide metabolism between humans and mice.

Genome editing of Nf1, Pten, and Trp53 in neonatal mice induces glioblastomas positive for oligodendrocyte lineage transcription factor 2.

To generate a mouse glioblastoma model by genome editing, we introduced Cas9 protein and guide RNAs specific for Nf1, Pten, and Trp53 into the neonatal mouse forebrain by electroporation. We found a high incidence (approximately 90%) of glial tumor development, including glioblastomas, 15 weeks later. The histological features of the tumors were similar to those of diffuse gliomas and, in some cases, similar to human glioblastomas, with microvascular proliferation (glomeruloid structure). In addition, unlike glial fibrillary acidic protein (GFAP)-positive glioblastomas generated using a similar method in a previous model, the majority of tumor cells were positive for oligodendrocyte lineage transcription factor 2, but negative for GFAP and neurofilaments. One base pair insertions identical to those seen in a previous model were found around the target sequences in Nf1, Pten, and Trp53, and additional deletions were found only in Pten. Considering that the histological characteristics were different from those seen in the previous model, our new model provides an additional research tool to investigate the early stages of glioblastoma development.

Generation of insulin-producing cells from the mouse liver using ß cell-related gene transfer including Mafa and Mafb.

Recent studies on the large Maf transcription factors have shown that Mafb and Mafa have respective and distinctive roles in ß-cell development and maturation. However, whether this difference in roles is due to the timing of the gene expression (roughly, expression of Mafb before birth and of Mafa after birth) or to the specific function of each gene is unclear. Our aim was to examine the functional differences between these genes that are closely related to ß cells by using an in vivo model of ß-like cell generation. We monitored insulin gene transcription by measuring bioluminescence emitted from the liver of insulin promoter-luciferase transgenic (MIP-Luc-VU) mice. Adenoviral gene transfers of Pdx1/Neurod/Mafa (PDA) and Pdx1/Neurod/Mafb (PDB) combinations generated intense luminescence from the liver that lasted for more than 1 week and peaked at 3 days after transduction. The peak signal intensities of PDA and PDB were comparable. However, PDA but not PDB transfer resulted in significant bioluminescence on day 10, suggesting that Mafa has a more sustainable role in insulin gene activation than does Mafb. Both PDA and PDB transfers ameliorated the glucose levels in a streptozotocin (STZ)-induced diabetic model for up to 21 days and 7 days, respectively. Furthermore, PDA transfer induced several gene expressions necessary for glucose sensing and insulin secretion in the liver on day 9. However, a glucose tolerance test and liver perfusion experiment did not show glucose-stimulated insulin secretion from intrahepatic ß-like cells. These results demonstrate that bioluminescence imaging in MIP-Luc-VU mice provides a noninvasive means of detecting ß-like cells in the liver. They also show that Mafa has a markedly intense and sustained role in ß-like cell production in comparison with Mafb.

Bioluminescence imaging of ß cells and intrahepatic insulin gene activity under normal and pathological conditions.

In diabetes research, bioluminescence imaging (BLI) has been applied in studies of ß-cell impairment, development, and islet transplantation. To develop a mouse model that enables noninvasive imaging of ß cells, we generated a bacterial artificial chromosome (BAC) transgenic mouse in which a mouse 200-kbp genomic fragment comprising the insulin I gene drives luciferase expression (Ins1-luc BAC transgenic mouse). BLI of mice was performed using the IVIS Spectrum system after intraperitoneal injection of luciferin, and the bioluminescence signal from the pancreatic region analyzed. When compared with MIP-Luc-VU mice [FVB/N-Tg(Ins1-luc)VUPwrs/J] expressing luciferase under the control of the 9.2-kbp mouse insulin I promoter (MIP), the bioluminescence emission from Ins1-luc BAC transgenic mice was enhanced approximately 4-fold. Streptozotocin-treated Ins1-luc BAC transgenic mice developed severe diabetes concomitant with a sharp decline in the BLI signal intensity in the pancreas. Conversely, mice fed a high-fat diet for 8 weeks showed an increase in the signal, reflecting a decrease or increase in the ß-cell mass. Although the bioluminescence intensity of the islets correlated well with the number of isolated islets in vitro, the intensity obtained from a living mouse in vivo did not necessarily reflect an absolute quantification of the ß-cell mass under pathological conditions. On the other hand, adenovirus-mediated gene transduction of ß-cell-related transcription factors in Ins1-luc BAC transgenic mice generated luminescence from the hepatic region for more than 1 week. These results demonstrate that BLI in Ins1-luc BAC transgenic mice provides a noninvasive method of imaging islet ß cells and extrapancreatic activity of the insulin gene in the liver under normal and pathological conditions.

Real-time monitoring of inflammation status in 3T3-L1 adipocytes possessing a secretory Gaussia luciferase gene under the control of nuclear factor-kappa B response element.

We have established 3T3-L1 cells possessing a secretory Gaussia luciferase (GLuc) gene under the control of nuclear factor-kappa B (NF-κB) response element. The 3T3-L1 cells named 3T3-L1-NF-κB-RE-GLuc could differentiate into adipocyte as comparably as parental 3T3-L1 cells. Inflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-1ß induced GLuc secretion of 3T3-L1-NF-κB-RE-GLuc adipocytes in a concentration- and time-dependent manner. GLuc secretion of 3T3-L1-NF-κB-RE-GLuc adipocytes was also induced when cultured with RAW264.7 macrophages and was dramatically enhanced by lipopolysaccharide (LPS)-activated macrophages. An NF-κB activation inhibitor BAY-11-7085 and an antioxidant N-acetyl cysteine significantly suppressed GLuc secretion induced by macrophages. Finally, we found that rosemary-derived carnosic acid strongly suppressed GLuc secretion induced by macrophages and on the contrary up-regulated adiponectin secretion. Collectively, by using 3T3-L1-NF-κB-RE-GLuc adipocytes, inflammation status can be monitored in real time and inflammation-attenuating compounds can be screened more conveniently.

Adipocyte-derived microvesicles contain RNA that is transported into macrophages and might be secreted into blood circulation.

We have recently found that 3T3-L1 adipocytes secrete microvesicles, known as adipocyte-derived microvesicles (ADMs), with angiogenic activity. In this study, we found that ADMs contain RNA without typical 28S and 18S ribosomal RNA inside the vesicles. Microarray analysis revealed that ADMs contain approximately 7000 mRNAs and 140 microRNAs. Most of transcripts for adipocyte-specific and dominant genes were contained in the ADMs, and their abundance was mostly correlated with that in the donor cells. Abundance of adipocyte-related microRNAs was also mostly correlated with that in the donor cells. ADMs mediated transport of adiponectin and resistin gene transcripts into RAW264.7 macrophages. Moreover, adipocyte-specific gene transcripts such as adiponectin, resistin, and PPARgamma2 were found in microvesicles isolated from rat serum. Thus, ADM might play a role as a novel intercellular communication tool by transporting RNA in paracrine and possibly endocrine manners.