TYSND1 (trypsin-like peroxisomal matrix peptidase 1) is a serine protease that functions as a critical regulator of peroxisomal protein processing and lipid metabolism. TYSND1 mediates removal of leader peptides from PTS2-containing proteins and processes multiple PTS1-containing enzymes involved in very-long-chain fatty acid β-oxidation 1. The enzyme catalyzes proteolytic maturation of key β-oxidation enzymes including Acox1, Hsd17b4, and ScpX, with TYSND1 knockdown resulting in accumulation of premature enzyme forms and significantly reduced peroxisomal fatty acid oxidation capacity 1. TYSND1's protease activity is self-regulated through autocleavage from a 60-kDa form to inactivated 15- and 45-kDa fragments, which are subsequently degraded by peroxisomal Lon protease 1. In vivo, TYSND1 deficiency causes peroxisomal localization defects of PTS2 substrates including Phyh and Agps, resulting in male infertility with acrosomal abnormalities and liver dysfunction following phytanol exposure—phenotypes resembling Zellweger syndrome spectrum disorders 2. TYSND1 expression is upregulated in lipid-related metabolic processes via PPAR signaling during inflammatory stress 3, suggesting its role extends beyond basal fatty acid catabolism to adaptive lipid metabolism responses.