Objective:To determine the expression of transmembrane protein 45A (TMEM45A) in keloid tissues and fibroblasts, and to evaluate its effect on extracellular matrix (ECM) synthesis by keloid-derived fibroblasts (KFs) .Methods:Samples of surgically excised keloid and normal foreskin tissues were collected from the Department of Dermatology and Department of Urology of Yanbian University Hospital from January 2019 to December 2020, and TMEM45A protein expression was determined in keloid tissues and KFs by Western blot analysis. KFs were divided into TMEM45A-specific small interfering RNA (siRNA) group and control siRNA group to be transfected with the TMEM45A-specific siRNA and control siRNA respectively. Then, Western blot analysis was performed to evaluate the effects of down-regulation of the TMEM45A gene on the expression of myofibroblast marker protein (α-smooth muscle actin) and ECM-related proteins.Results:Compared with normal skin tissues (1.00 ± 0.11) and fibroblasts (1.00 ± 0.20), TMEM45A expression levels significantly decreased in keloid tissues (0.26 ± 0.05) and KFs (0.41 ± 0.09), respectively ( t = 10.76, 4.75, P < 0.001, = 0.009, respectively). The expression levels of α-smooth muscle actin, ECM-related type Ⅰ collagen, type Ⅲ collagen, and fibronectin were significantly higher in the TMEM45A-specific siRNA group than in the control siRNA group ( t = -5.98, -4.57, -4.90, -7.19, P = 0.004, 0.010, 0.008, 0.002, respectively) . Conclusion:Lowly expressed TMEM45A in keloids may play an important role in the pathogenesis of keloids by promoting ECM synthesis.