Knockout of THBS1 gene improves immune microenvironment of visceral fat and inhibits intraperitoneal implantation and metastasis of colorectal cancer in mice

To investigate the effects of thrombospondin1（THBS1）gene knockout on immune microenvironment and tumor progression of colorectal cancer.

THBS1 gene knockout（THBS1^-/-）mice were constructed and its genotypes were determined by PCR and agarose gel electrophoresis. Subcutaneous tumor bearing and intraperitoneal implantation metastasis models of colorectal cancer were constructed in wild type（WT）and THBS1^-/- mice to observe the effect of THBS1 on tumor growth. Immune cells in epididymal adipose of tumor bearing mice of both types were detected by flow cytometry.

Compared with the WT mice, THBS1^-/- mice showed no difference in tumor growth in colorectal cancer subcutaneous tumor bearing model（P>0.05）, but significantly inhibited tumor growth in intraperitoneal implantation metastasis model（P<0.05）. Subsequently, flow cytometry indicated that the proportion of total macrophages in the epididymal adipose tissue was increased in the THBS1^-/- mice than the WT mice（P<0.01）, with the proportion of M1-like macrophages（typical or proinflammatory type）increased（P<0.01）and that of M2-like macrophages（alternately activated or anti-inflammatory type）decreased（P<0.01）. The proportion of myeloid-derived suppressor cells（MDSC）was decreased（P<0.05）, that of Ly6C subgroup was increased（P<0.01）, that of Ly6G subgroup was decreased（P<0.05）, that of CD8⁺ T cells was significantly increased（P<0.01）, and that of CD4⁺ T cells was decreased（P<0.01）. There were no changes in the proportions of total macrophages, M1-like macrophages and M2-like macrophages in the peripheral blood of intraperitoneal implantation metastasis model mice（P>0.05）. The proportions of MDSC and ly6C subgroup were not changed（P>0.05）, while that of ly6G subgroup were decreased（P<0.05）. The proportion of CD8⁺ T cells was significantly decreased（P<0.05）, while that of CD4⁺ T cells was not changed（P>0.05）.

THBS1 gene knockout inhibits the intraperitoneal metastasis of colorectal cancer cells by enhancing tumor immunity.