TIPE1 accelerates atherogenesis by inducing endothelial dysfunction in response to oxidative stress.

Atherosclerosis is an inflammatory disease of the arterial wall, which involves endothelial cells and immune cells. Endothelial dysfunction has been considered an important step in the initiation of the disease. TIPE1 is a newly identified protein of the TIPE family, and plays a vital role in inflammation and tumorigenesis. However, its role in atherogenesis remains unclear. In this study, we demonstrated that TIPE1 promoted atherogenesis by inducing endothelial dysfunction. When human umbilical vein endothelial cells (HUVECs) were exposed to oxidative stress, the level of TIPE1 was significantly up-regulated, and the ROS generation markedly increased in TIPE1 over-expressing HUVECs. As a result, the growth of HUVECs was inhibited, and the apoptosis was enhanced. However, the cell contact ability between HUVECs and THP-1 cells were augmented due to the up-regulation of adhesion molecules such as E-selectin and ICAM-1 induced by TIPE1 overexpression. Importantly, ApoE-/- mice injected with TIPE1 recombinant lentivirus developed significantly severe atherosclerosis accompanied by hyperglycemia, hypercholesterolemia and increased white blood count. These findings indicated that excessive ROS induced by the overexpression of TIPE1 in endothelial cells accelerated the process of atherogenesis.

Clinical Significance of TIPE2 Protein Upregulation in Non-Hodgkin's Lymphoma.

Non-Hodgkin's lymphoma (NHL), which includes diffuse large B-cell lymphoma (DLBCL) and peripheral T-cell lymphoma, is a refractory malignant tumor originated from the lymphatic system. TNFAIP8L2 (TIPE2 or tumor necrosis-alpha-induced protein-8 like 2) is a negative regulator for inflammation and an inhibitor for carcinogenesis. However, whether TIPE2 plays a role in lymphomagenesis is unknown. In this study, we determined TIPE2 expression in NHL by immunohistochemistry and investigated its clinicopathological significance in DLBCL. We found that TIPE2 expression was upregulated in both DLBCL and peripheral T-cell lymphoma. But the expression of TIPE2 in T lymphomas was weaker than that in DLBCL. Interestingly, among DLBCL, TIPE2 expression was significantly stronger in the germinal center B-cell (GCB) type than in the non-GCB type. These results suggest that the expression of TIPE2 protein could be a predictor of better prognosis for DLBCL.

TIPE2 protein prevents injury-induced restenosis in mice.

Proliferation of vascular smooth muscle cells (VSMCs) plays an important role in restenosis, a disease characterized by smooth muscle cell hyperplasia and neointimal formation. How proliferation signals are controlled to avoid restenosis is not fully understood. Here we report that TIPE2, the tumor necrosis factor (TNF) α-induced protein 8-like 2 (TNFAIP8L2), suppresses injury-induced restenosis by inhibiting VSMCs proliferation. TIPE2 was significantly upregulated in VSMCs in response to PDGF-BB stimuli and injury. Enforced TIPE2 expression significantly suppressed VSMCs proliferation and cell cycle progression, whereas TIPE2 deficiency in VSMCs promoted cell proliferation and upregulated the expression of Cyclins D1 and D3. TIPE2 likely regulated VSMC proliferation via Rac1-STAT3 and ERK1/2 signaling pathways. It blocked STAT3 activation and nuclear translocation in a Rac1-dependent manner. As a result, TIPE2-deficient VSMCs exhibited enhanced proliferation whereas TIPE2-deficient mice developed more severe restenosis in response to vascular injury. Conversely, adenovirus-mediated gene transfer of TIPE2 significantly reduced injury-induced restenosis in mice. These results indicate that TIPE2 plays a suppressive role in injury-induced restenosis and may serve as a new therapeutic target for treating the disease.

TIPE2 negatively regulates inflammation by switching arginine metabolism from nitric oxide synthase to arginase.

TIPE2, the tumor necrosis factor (TNF)-alpha-induced protein 8-like 2 (TNFAIP8L2), plays an essential role in maintaining immune homeostasis. It is highly expressed in macrophages and negatively regulates inflammation through inhibiting Toll-like receptor signaling. In this paper, we utilized RAW264.7 cells stably transfected with a TIPE2 expression plasmid, as well as TIPE2-deficient macrophages to study the roles of TIPE2 in LPS-induced nitric oxide (NO) and urea production. The results showed that TIPE2-deficiency significantly upregulated the levels of iNOS expression and NO production in LPS-stimulated macrophages, but decreased mRNA levels of arginase I and urea production. However, TIPE2 overexpression in macrophages was capable of downregulating protein levels of LPS-induced iNOS and NO, but generated greater levels of arginase I and urea production. Furthermore, TIPE2-/- mice had higher iNOS protein levels in lung and liver and higher plasma NO concentrations, but lower levels of liver arginase I compared to LPS-treated WT controls. Interestingly, significant increases in IκB degradation and phosphorylation of JNK, p38, and IκB were observed in TIPE2-deficient macrophages following LPS challenge. These results strongly suggest that TIPE2 plays an important role in shifting L-arginase metabolism from production of NO to urea, during host inflammatory response.

TIPE2 deficiency accelerates neointima formation by downregulating smooth muscle cell differentiation.

Phenotypic switching of vascular smooth muscle cells (VSMCs) is known to play a key role in the development of atherosclerosis. However, the mechanisms that mediate VSMC phenotypic switching are unclear. We report here that TIPE2, the tumor necrosis factor (TNF) α-induced protein 8-like 2 (TNFAIP8L2), plays an atheroprotective role by regulating phenotypic switching of VSMCs in response to oxidized low-density lipoprotein (ox-LDL) stimuli. TIPE2-deficient VSMCs treated with ox-LDL expressed lower levels of contractile proteins such as SMαA, SM-MHC and calponin, whereas the proliferation, migration and the synthetic capacity for growth factors and cytokines were increased remarkably. Furthermore, TIPE2 inhibited VSMCs proliferation by preventing G 1/S phase transition. Interestingly, these effects of TIPE2 on VSMCs were dependent on P38 and ERK1/2 kinase signals. As a result, neointima formation was accelerated in the carotid arteries of TIPE2-deficient mice. These results indicate that TIPE2 is a potential inhibitor of atherosclerosis.