The Role And Mechanism Of Hypoxia Invovled In The Outcome Of Ameloblastoma

OBJECTIVE:As the most common oral and maxillofacial benign odontogenic tumor, ameloblastoma (AM) always leads clinical surgeons into a dilemma because of it’s biological behaviors like high aggressiveness and high postoperative recurrence rate, as well as it’s diverse pathological types. Hypoxia is one of the general characteristics of tumors’microenvironment. In the hypoxia microenvironment, tumor cells take place a series of responses like increasing angiogenesis and secreting MMPs, to maintain energy metabolism and to realize invasion and metastasis. Relevant research indicates that hypoxia-inducible factor-1(HIF-1), a hypoxic response regulatory factor which is very common in a variety of tumors’cells, closely relates with tumor cells’proliferation, apoptosis, invasion and metastasis by maintaining their energy metabolism and facilitating angiogenesis through regulating the expression of various target genes. HIF-1is a heterodimeric transcription factor composed of a subunit and β subunit. Of the two subunits, a subunit is the only oxygen regulatory subunit, and it determines the activity of HIF-1. In this research, we detected the expression of HIF-1α, Id-1, VEGF and MMP-2/MMP-9in ameloblastoma tissues, in order to explore the possible relationship between hypoxia and AM. On a long view, we expect to provide an advanced look into the mechanism of AM’s occurrence, progression and invasion.METHODS:1. Immunohistochemical staining (SP) was used to detect the expression of HIF-la, Id-1, VEGF and MMP-2/MMP-9in mural/unicystic ameloblastoma. The specimens were collected from patients treated with marsupialization joint resection operation at Oral and Maxillofacial Surgery Department of Qilu Hospital, Shandong University from year2008to2011.2. Tumor tissue and peritumoral normal gingival tissue was resected and picked up through surgeries from patients with solid ameloblastoma at Oral and Maxillofacial Surgery Department of Qilu Hospital from year2011to2012, meanwhile, pathological sections diagnosed as solid ameloblastoma were also collected. Immunohistochemical staining (SP) was used to detect the expression of HIF-la, Id-1, VEGF and MMP-2/MMP-9in these specimens.3. Protein and RNA was extracted from tumor tissue and peritumoral normal gingival tissue which was resected from patients with solid ameloblastoma at Oral and Maxillofacial Surgery Department of Qilu Hospital from year2011to2012, Afterwards, Western Blot and FQ-PCR were conducted to investigate the expression of HIF-1α at protein and mRNA level respectively.RESULTS:1. In the tissue which was resected from patients with mural AM in the phase Ⅰ surgery (marsupialization), the protein expression of HIF-la was obvious and the positive cells’ rate>50%. After marsupialization treatment, the tumor diminished accompanying by the local tissues’repair process, and HIF-la expression wasn’t detected in the resected tissues of the phase Ⅱ surgery (resection). Meanwhile, we found that the expression of Id-1, VEGF and MMP-2/MMP-9in these specimens was consistent with that of HIF-la.2. In patients’tissue specimens of solid ameloblastoma, the positive rate of tumor group was68.75% (11/16), nevertheless, the control group’s positive rate was16.67%(1/6), and the between-group difference was statistically significant (P<0.05). The rate of positive cells in the tumor group was in the range of13%-83%(mean39.33%). Meanwhile, in the specimens of which HIF-la was positively detected, the expression of Id-1, VEGF, MMP-2/MMP-9was obvious, and was significantly different from that of control group.3. In both tumor tissue and peritumoral normal gingival tissue of patients with solid ameloblastoma, the mRNA expression of HIF-1α was detected. Comparing with peritumoral normal gingival tissue, the relative expression level of HIF-1α mRNA in tumor tissue was in the range of1.04～1.14(mean1.08±0.04).4. The protein expression of HIF-1α was detected obviously high in tumor tissue of solid AM through Western Blot, nevertheless, little in control group (normal gingiva tissue around tumor).CONCLUSION:The local hypoxia microenvironment influences occurrence, progression and invasion of AM. In the hypoxia microenvironment, HIF-1α expresses higher, and up-regulates Id-1, VEGF and MMP-2/MMP-9. Consequently, angiogenesis and vessels permeability was increased, and ECM was destroyed. Finally, tumor cells fit for the hypoxia microenvironment, and develop aggressively.Using marsupialization to treat mural/unicystic AM may destroy local hypoxic microenvironment, consequently, the pathway through which the active HIF-1regulates various target genes to promote tumors’ invasion and development was blocked. Meanwhile, intra-cystic pressure was released. Ultimately, the tumor’s behavior was influenced and the local tissue has been repaired slowly.