Blood vessels play a crucial role in maintaining the stem cell niche in both tumours and developing organs. Cell competition is critical for tumour progression. We hypothesise that blood vessels may act as a regulator of this process. As a pioneer, the secretions of blood vessels regulate the intensity of cell competition, which is essential for tumour invasion and developmental organ extension. Brd4 expresses highly in endothelial cells within various tumours and is positively correlated with numerous invasive genes, making it an ideal focal point for further research on the relationship between blood vessels and cell competition. Our results indicated that the absence of endothelial Brd4 led to a reduction in neural stem cell mortality and compromised cell competition. Endothelial Brd4 regulated cell competition was dependent on Testican2. Testican2 was capable of depositing Sparc and acted as a suppressor of Sparc. Compromised cell competition resulted in the depletion of neural stem cells and accelerated brain ageing. Testican2 could rescue the run-off of neural stem cells and accelerate the turnover rate of neurons. AD patients show compromised cell competition. Through the cloning of a point mutant of Brd4 identified in a subset of AD patients, it was demonstrated that the mutant lacked the ability to promote cell competition. This study suggests a novel approach for treating age-related diseases by enhancing the intensity of cell competition.