Increased migration by stimulation of thymidine phosphorylase in endothelial cells of different origin

Netrin-1 promotes epithelium repair in corneal injury

AIM

To explore netrin-1 functions on corneal epithelium in vitro and in vivo.

METHODS

In vitro the human corneal epithelial (HCE) cells were treated with serum free DMEM-F12 basic media containing 0, 50, 100, 200, 300, 500, 800, and 1000 ng/mL of netrin-1, respectively. The cells viability was detected by cell counting kit-8 (CCK-8). The wound-healing assay was applied to assess the migration proficiency of HCE cells. Flow cytometry was used to analyze the cell-cycle distribution and apoptosis. In vivo, normal c57 (6wk) mice were demarcated with a trephine in the middle of the cornea to produce a 3-mm circular wound. Mice corneas were inflicted no epithelium with a 3-mm wound displayed, but remained the limbal epithelium intact. A blunt scalpel blade was used to remove the corneal epithelian cells, followed by topical netrin-1 application (200 ng/mL), and the group treated by PBS as control. The treated group was injected netrin-1 into the normal c57 mice inferior subconjunctival 4h before trauma. Mouse corneal inflammation and neovascularization were observed under slit lamp microscope. The apoptosis of corneal cells was determined by TUNEL staining.

RESLUTS

A concentration of 200 ng/mL netrin-1 enhanced 25% of the HCE viability. The relative migration rates were 76.3% and 100% in control and netrin-1 treated group after cultured 72h. Treated with netrin-1 (200 ng/mL) decreased the apoptosis of HCE cells, as well as decreased their percentage from 19.3%±0.57% to 12.7%±0.42% of the total. The remaining wound area was 1.22 mm² in control group but 0.22 mm² in the netrin-1 treated group. Exogenous Netrin-1 inhibits apoptosis of corneal epithelial cells of c57 mice. TUNEL-positive cells at the epithelial layer of the corneas of the control and netrin-1 treated c57 mice at 24h after wounding were 43.3% and 16.7% respectively.

CONCLUSION

Netrin-1 can reduce HCE apoptosis as well as promote its proliferation and migration. Topical application of netrin-1 promotes the injuryed cornea epithelial wound repair and inhibits apoptosis of corneal epithelial cells. These findings may offer potential therapies to repair the defects of corneal epithelial based on netrin-1.

Thymidine Phosphorylase in Cancer; Enemy or Friend?

Thymidine phosphorylase (TP) is a nucleoside metabolism enzyme that plays an important role in the pyrimidine pathway.TP catalyzes the conversion of thymidine to thymine and 2-deoxy-α-D-ribose-1-phosphate (dRib-1-P). Although this reaction is reversible, the main metabolic function of TP is catabolic. TP is identical to the angiogenic factor platelet-derived endothelial-cell growth factor (PD-ECGF). TP is overexpressed in several human cancers in response to cellular stressful conditions like hypoxia, acidosis, chemotherapy and radiotherapy. TP has been shown to promote tumor angiogenesis, invasion, metastasis, evasion of the immune-response and resistance to apoptosis. Some of the biological effects of TP are dependent on its enzymatic activity, while others are mediated through cytokines like interleukin 10 (IL-10), basic fibroblast growth factor (bFGF) and tumour necrosis factor α (TNFα). Interestingly, TP also plays a role in cancer treatment through its role in the conversion of the oral fluoropyrimidine capecitabine into its active form 5-FU. TP is a predictive marker for fluoropyrimidine response. Given its various biological functions in cancer progression, TP is a promising target in cancer treatment. Further translational research is required in this area.

Therapeutic effects of topical netrin-4 inhibits corneal neovascularization in alkali-burn rats

Netrins are secreted molecules involved in axon guidance and angiogenesis. However, the role of netrins in the vasculature remains unclear. Netrin-4 and netrin-1 have been found to be either pro- or antiangiogenic factors. Previously, we found that netrin-1 acts as an anti-angiogenic factor in rats by inhibiting alkali burn-induced corneal neovascularization. Here, we further investigate the effects of netrin-4, another member of the same netrin family, on neovascularization in vitro and in vivo. We found that netrin-4 functions similarly as netrin-1 in angiogenesis. In vitro angiogenesis assay shows that netrin-4 affected human umbilical vein endothelial cell (HUVEC) tube formation, viability and proliferation, apoptosis, migration, and invasion in a dose-dependent manner. Netrin-4 was topically applied in vivo to alkali-burned rat corneas on day 0 (immediately after injury) and/or day 10 post-injury. Netrin-4 subsequently suppressed and reversed corneal neovascularization. Netrin-4 inhibited corneal epithelial and stromal cell apoptosis, inhibited vascular endothelial growth factor (VEGF), but promoted pigment epithelium-derived factor (PEDF) expression, decreased NK-KB p65 expression, and inhibits neutrophil and macrophage infiltration. These results indicate that netrin-4 shed new light on its potential roles in treatmenting for angiogenic diseases that affect the ocular surface, as well as other tissues.

Thymidine phosphorylase in cancer cells stimulates human endothelial cell migration and invasion by the secretion of angiogenic factors

Background:

Thymidine phosphorylase (TP) is often overexpressed in tumours and has a role in tumour aggressiveness and angiogenesis. Here, we determined whether TP increased tumour invasion and whether TP-expressing cancer cells stimulated angiogenesis.

Methods:

Angiogenesis was studied by exposing endothelial cells (HUVECs) to conditioned medium (CM) derived from cancer cells with high (Colo320TP1=CT-CM, RT112/TP=RT-CM) and no TP expression after which migration (wound-healing-assay) and invasion (transwell-assay) were determined. The involvement of several angiogenic factors were examined by RT–PCR, ELISA and blocking antibodies.

Results:

Tumour invasion was not dependent on intrinsic TP expression. The CT-CM and RT-CM stimulated HUVEC-migration and invasion by about 15 and 40%, respectively. Inhibition by 10 μM TPI and 100 μM L-dR, blocked migration and reduced the invasion by 50–70%. Thymidine phosphorylase activity in HUVECs was increased by CT-CM. Reverse transcription-polymerase chain reaction revealed a higher mRNA expression of bFGF (Colo320TP1), IL-8 (RT112/TP) and TNF-α, but not VEGF. Blocking antibodies targeting these factors decreased the migration and invasion that was induced by the CT-CM and RT-CM, except for IL-8 in CT-CM and bFGF in RT-CM.

Conclusion:

In our cell line panels, TP did not increase the tumour invasion, but stimulated the migration and invasion of HUVECs by two different mechanisms. Hence, TP targeting seems to provide a potential additional strategy in the field of anti-angiogenic therapy.

Accumulation of thymidine-derived sugars in thymidine phosphorylase overexpressing cells

Thymidine phosphorylase (TP) is often overexpressed in cancer and potentially plays a role in the stimulation of angiogenesis. The exact mechanism of angiogenesis induction is unclear, but is postulated to be related to thymidine-derived sugars. TP catalyzes the conversion of thymidine (TdR) to thymine and deoxyribose-1-phosphate (dR-1-P), which can be converted to dR-5-P, glyceraldehyde-3-phosphate (G3P) or deoxyribose (dR). However, it is unclear which sugar accumulates in this reaction. Therefore, in the TP overexpressing Colo320 TP1 and RT112/TP cells we determined by LC-MS/MS which sugars accumulated, their subcellular localization (using (3)H-TdR) and whether dR was secreted from the cells. In both TP-overexpressing cell lines, dR-1-P and dR-5-P accumulated intracellularly at high levels and dR was secreted extensively by the cells. A specific inhibitor of TP completely blocked TdR conversion, and thus no sugars were formed. To examine whether these sugars may be used for the production of angiogenic factors or other products, we determined with (3)H-TdR in which subcellular location these sugars accumulated. TdR-derived sugars accumulated in the cytoskeleton and to some extent in the cell membrane, while incorporation into the DNA was responsible for trapping in the nucleus. In conclusion, various metabolic routes were entered, of which the TdR-derived sugars accumulated in the cytoskeleton and membrane. Future studies should focus on which exact metabolic pathway is involved in the induction of angiogenesis.