Granulin Family. Granulins are small peptides derived from a larger precursor (PC cell-derived growth factor, granulin/epithein precursor, 88 kDa glycoprotein, proepithelin, acrogranin, or progranulin), which can be cleaved by several enzymes. PGRN cleavage releases seven full-length granulin domains (G, F, B, A, C, D, E) and one half-length paragranulin domain (P). Secretory leukocytes protease inhibitor (SLPI) or high-density lipoprotein/apolipoprotein A-1 (HDL-Apo A1) binding to the full-length PGRN prevents its proteolytic process.