CD73 regulates vascular smooth muscle cell functions and facilitates atherosclerotic plaque formation.

Extracellular adenosine, generated by ecto-5'-nucleotidase (CD73) via enzymatic catalyzation, has been found to facilitate atherosclerosis (AS). Thus, suppressing CD73 may attenuate AS. In this study, we evaluated the role of CD73 during AS development and further explored cellular and molecular mechanism in smooth muscle cells (SMCs). In a mouse model of carotid artery ligation, inactivation of CD73 inhibited migration and proliferation of vascular SMCs. In in vitro experiments, RNA interference of CD73 inhibited migration, proliferation, and foam cell transformation of human umbilical artery smooth muscle cells. Further, we established an atherosclerotic model using ApoE-/- mice fed with a western diet for 16 weeks. Inactivation of CD73-attenuated AS and hyperlipidemia in ApoE-/- mice. In conclusion, our data suggest that CD73 facilitates AS by promoting migration, proliferation, and foam cell transformation of vascular SMCs and elevating serum lipid levels. Thus, inhibition of CD73 may be beneficial for prevention and treatment of AS.

Short- and long-term toxicities of multi-walled carbon nanotubes in vivo and in vitro.

As nanomaterials are developed and applied, their potential for health hazards needs to be determined. In the present study, we used commercial nude multi-walled carbon nanotubes (MWCNTs) trimmed to a short length (50-200 nm; s-MWCNTs) and synthesized functionalized MWCNTs with polyethylene glycol (PEG) (s-MWCNTs-PEG). We then studied the toxic effects of s-MWCNTs and s-MWCNTs-PEG on cultured cells and in a mouse model. Peripheral haemograms and various biochemical markers of the heart, liver and kidney were measured. We found no toxicity of either type of nanotube on the viability of human SKBR-3 breast carcinoma cells or control cells. There were no differences in vivo on inflammatory responses, the coagulation system, haemograms or vital organ functions between the test and control groups. Additionally, we found no toxicity of these nanotubes on male mouse sperm production or mutagenesis in the long term. In conclusion, both s-MWCNTs and s-MWCNTs-PEG displayed good in vitro and in vivo biocompatibility, making future applications in biology and clinical therapy as a carrier for drug delivery feasible.

CD73 protects kidney from ischemia-reperfusion injury through reduction of free radicals.

Renal ischemia-reperfusion injury (IRI) may cause severe systemic diseases. Extracellular adenosine is anti-inflammatory especially during hypoxemia. As ecto-5'-nucleotidase (CD73) is the rate-limiting enzyme for extracellular adenosine generation, it may protect renal IRI through adenosine production. In the current studies, we investigated the effects of CD73 in genetically modified mice. We found that renal IRI caused more serious histological injury, vascular permeability, and lipid peroxidation in CD73(-/-) than that in CD73(+/+) mice. In addition, AMP and free radical concentrations were much higher in CD73(-/-) than that in CD73(+/+) mice. Our data support the fact that CD73 may protect the kidney from IRI through adenosine production and a reduction of free radicals.

RNAi-mediated CD73 suppression induces apoptosis and cell-cycle arrest in human breast cancer cells.

Ecto-5'-nucleotidase (CD73), a cell surface protein that hydrolyzes extracellular AMP into adenosine and phosphate, is overexpressed in many solid tumors. In this study, we tested the hypothesis that increased CD73 may promote tumor progression by examining the effect of CD73 suppression via RNA interference and CD73 overexpression on tumor growth in vivo and in vitro. Using digitized whole-body images, plate clone forming assay and TUNEL assay in frozen tissue sections, we found that the cell growth rate was significantly lower in vivo and in vitro after CD73 suppression and late apoptosis was much higher in xenograft tumors developed from the CD73-siRNA transfected MB-MDA-231 clone (P1). By flow cytometry, the P1 cell cycle was arrested in the G0/G1 phase. Moreover, Bcl-2 was downregulated, while Bax and caspase-3 were upregulated with CD73 suppression. CD73 inhibitor α,ß-methylene adenosine-5'-disphosphate (APCP) functioned similarly with RNAi-mediated CD73 suppression. In addition, in transfected MCF-7 cells, we found that CD73 overexpression increased cell viability and promoted cell cycle progression, depending on its enzyme activity. More intriguingly, CD73 overexpression in MCF-7 breast cancer cells produces a tumorigenic phenotype. We conclude that CD73 plays an important role in breast cancer growth by affecting cell cycle progression and apoptosis.