Bone marrow endothelial progenitor cells activate hepatic stellate cells and aggravate carbon tetrachloride induced liver fibrosis in mice via paracrine factors.

OBJECTIVES: Bone marrow derived endothelial progenitor cells (BM-EPCs) are increased in chronic liver disease (CLD). Their role in hepatic fibrosis and regeneration remains an area of intense studies. We investigated the migration and secretory functions of BM-EPCs in fibrotic mice liver. MATERIALS AND METHODS: Bone marrow cells from C57BL6-GFP mice were transplanted into the femur of irradiated C57BL6 mice, followed by CCl4 doses for 8 weeks, to develop hepatic fibrosis (n = 36). Transplanted C57BL6 mice without CCl4 treatment were used as controls. EPCs were analyzed in BM, blood and liver by flow cytometry and immunofluorescence. VEGF and TGF-ß were analysed in the hepatic stellate cells (HSCs) and BM-EPCs co-cultures using ELISAs. RESULTS: There was a significant migration of EPCs from BM to blood and to the liver (P ≤ 0.01). Percentage of GFP+ CD31+ EPCs and collagen proportionate area was substantially increased in the liver at 4th week of CCl4 dosage compared to the controls (19.8% vs 1.9%, P ≤ 0.05). Levels of VEGF (533.6 pg/ml) and TGF-ß (327.44 pg/ml) also increased significantly, when HSCs were treated with the EPC conditioned medium, as compared to controls (25.66 pg/ml and 5.87 pg/ml, respectively; P ≤ 0.001). CONCLUSIONS: Present findings suggest that BM-EPCs migrate to the liver during CCl4-induced liver injury and contribute to fibrosis.

Brain-specific knockdown of miR-29 results in neuronal cell death and ataxia in mice.

Several microRNAs have been implicated in neurogenesis, neuronal differentiation, neurodevelopment, and memory. Development of miRNA-based therapeutics, however, needs tools for effective miRNA modulation, tissue-specific delivery, and in vivo evidence of functional effects following the knockdown of miRNA. Expression of miR-29a is reduced in patients and animal models of several neurodegenerative disorders, including Alzheimer's disease, Huntington's disease, and spinocerebellar ataxias. The temporal expression pattern of miR-29b during development also correlates with its protective role in neuronal survival. Here, we report the cellular and behavioral effect of in vivo, brain-specific knockdown of miR-29. We delivered specific anti-miRNAs to the mouse brain using a neurotropic peptide, thus overcoming the blood-brain-barrier and restricting the effect of knockdown to the neuronal cells. Large regions of the hippocampus and cerebellum showed massive cell death, reiterating the role of miR-29 in neuronal survival. The mice showed characteristic features of ataxia, including reduced step length. However, the apoptotic targets of miR-29, such as Puma, Bim, Bak, or Bace1, failed to show expected levels of up-regulation in mice, following knockdown of miR-29. In contrast, another miR-29 target, voltage-dependent anion channel1 (VDAC1), was found to be induced several fold in the hippocampus, cerebellum, and cortex of mice following miRNA knockdown. Partial restoration of apoptosis was achieved by down-regulation of VDAC1 in miR-29 knockdown cells. Our study suggests that regulation of VDAC1 expression by miR-29 is an important determinant of neuronal cell survival in the brain. Loss of miR-29 results in dysregulation of VDAC1, neuronal cell death, and an ataxic phenotype.

Proximity of H2A.Z containing nucleosome to the transcription start site influences gene expression levels in the mammalian liver and brain.

Nucleosome positioning maps of several organisms have shown that Transcription Start Sites (TSSs) are marked by nucleosome depleted regions flanked by strongly positioned nucleosomes. Using genome-wide nucleosome maps and histone variant occupancy in the mouse liver, we show that the majority of genes were associated with a single prominent H2A.Z containing nucleosome in their promoter region. We classified genes into clusters depending on the proximity of H2A.Z to the TSS. The genes with no detectable H2A.Z showed lowest expression level, whereas H2A.Z was positioned closer to the TSS of genes with higher expression levels. We confirmed this relation between the proximity of H2A.Z and expression level in the brain. The proximity of histone variant H2A.Z, but not H3.3 to the TSS, over seven consecutive nucleosomes, was correlated with expression. Further, a nucleosome was positioned over the TSS of silenced genes while it was displaced to expose the TSS in highly expressed genes. Our results suggest that gene expression levels in vivo are determined by accessibility of the TSS and proximity of H2A.Z.