The Effect Of High-fat Diet On Pancreatic Cancer Tumor Microenvironment And Its Molecular Regulatory Mechanism

BackgroundPancreatic cancer is a digestive system tumor with an increasing incidence and a high degree of malignancy,of which the five-year survival is only 11.4%.Among pancreatic cancer,nearly 90%are pancreatic ductal adenocarcinoma(PDAC).At present,the main treatment for pancreatic cancer is surgery combined with chemotherapy,immunotherapy,targeted therapy and other comprehensive treatments according to the NCCN guidelines.However,85%of patients had no chance to undergo surgery at initial diagnosis.And patiente are always highly resistant to chemotherapy,immunotherapy,and targeted therapy.The resistance is strongly linked to the exclusive tumor microenvironment(TME)of pancreatic cancer.Pancreatic cancer is closely related to dietary elements.High-fat diet(HFD)is not only a risk factor for cardiovascular diseases,but also closely related to the occurrence and development of 13 types of cancer such as meningioma and breast cancer.It was found that the incidence and growth of pancreatic cancer were significantly increased under HFD compared to normal diet(ND),however,the effect of HFD on the TME of pancreatic cancer was not clear.Therefore,we analyzed the synergistic evolution of metabolic factors and tumors during the development of pancreatic cancer from multiple perspectives,and explored the regulatory mechanism involved to provide a theoretical basis for the development of potential treatment strategies.Objectives1.To clarify the effects of HFD on occurrence and development of murine pancreatic cancer;2.To analyze the effects of HFD on tumor microenvironment of murine pancreatic cancer by immunohistochemical staining technique;3.To explore the involved molecular mechanisms of the regulation of HFD in tumor microenvironment by transcriptome sequencing including both mRNA and non-coding RNA,to present potential diagnostic and therapeutic targets.Methods1.60%fat containing HFD was fed to C57BL/6J mice for more than 4 months and then KPC murine pancreatic cancer cells were injected into pancreas to establish murine pancreatic cancer model.Several weeks later,the mice were killed and the orthotopic tumors and abdominal dissemination were compared.2.Tumor samples from 5 cases of ND as well as 4 cases of HFD-fed mice were collected,and 2 immune cell populations,1 neovascularization marker,1 neo lymphatic duct marker,1 pathogenic marker,1 stellate cell marker were labeled and semi-quantitatively evaluated with immunohistochemical staining techniques.3.The transcriptome analysis including mRNA and non-coding RNA by using HT-sequencing technique was performed to discover the potential key molecules and signal pathways which were involved in the regulation of HFD in tumor microenvironment and as well,the clinical significance of these potential key factors was further studied by using bioinformatic methods.Results1.All of the tumors were palpable after 10d days of injection of tumor cells in 14 mice.No liver metastasis was observed in either group.In HFD group,the primary tumors were larger and the local invasion and abdominal dissemination was much severe than that in ND group.2.In HFD group,there was less CD8+cytotoxic T lymphocytes(CTL)infiltration and more M2 polarized tumor associated macrophage(TAM)infiltration.And as well,HFD substantially induced angiogenesis and lymph angiogenesis in tumor microenvironment which could potentially promote tumor growth and invasion.3.Transcriptomic and circular RNA sequencing results showed that a large number of differentially expressed mRNAs and circular RNAs(circRNAs)were present.These differentially expressed mRNAs and circRNAs were associated with fatty acid and amino acid metabolism,PPAR signaling pathway,etc.HFD may modulate the TME of pancreatic cancer through down regulating the expression of ITIH1、APOH and PROX1.Some of these key factors were significantly related with survival of pancreatic cancer patients.ConclusionHFD could promote growth,invasion of murine pancreatic cancer,probably by modulating microenvironment,including suppression of CTL,induction of M2 TAM,promoting angiogenesis and lymph angiogenesis.Alterations in fatty acid metabolism and down regulation of ITHI1,APOH and PROX1 gene may be important mechanisms involved,which could be potential diagnostic and therapeutic targets for comprehensive therapy of pancreatic cancer.