Identification of Novel Natural Substrates of Fibroblast Activation Protein-alpha by Differential Degradomics and Proteomics

Abstract

Fibroblast activation protein-␣ (FAP) can hydrolyze the postproline bond. We identified endogenous substrates of FAP in fibroblasts that were previously naive to both FAP and its proteolytic activity. FAP-dependent cleavage sites were identified in many extracellular matrix (ECM) and ECM-associated proteins including collagens and lysyl oxidase-like-1, and CSF-1, CXCL-5 and C1qT6. Quantitative proteomic analysis implicated FAP in ECM-cell interactions, coagulation and metabolism. This study greatly expands the repertoire of FAP substrates and shows that FAP has a role in coagulation in the mouse.

Fibroblast activation protein enzyme deficiency prevents liver steatosis, insulin resistance and glucose intolerance and increases fibroblast growth factor-21 in diet induced obese mice

“…Our discovery that ablating the FAP enzyme activity is sufficient to generate these metabolic outcomes indicates that these outcomes are driven by bioactive natural substrates of FAP. The known metabolism-associated substrates of FAP are FGF-21, GLP-1, NPY and PYY [1,3,5,20], and possibly nucleobindin-1 [44]. We showed here that GLP-1 activity is not altered and so is unlikely to be a physiological substrate of FAP.…”

“…FAP has previously been found only in activated fibroblasts, so the new observation of its expression in b-cells commences a paradigm shift in understanding FAP functions. In DIO, FAP is probably acting on nonextracellular matrix substrates derived from b-cells and neighbouring cells, perhaps some that were identified in our recent degradomics study [1]. FAP is relatively abundant in mouse serum, so that is probably a major site of substrate degradation, including FGF-21.…”

“…Fibroblast Activation Protein-alpha (FAP) is a unique extracellular serine protease of the dipeptidyl peptidase-4 (DPP4) family. FAP degrades many bioactive peptides [1]. Neuropeptide Y (NPY) and fibroblast growth factor-21 (FGF-21) are physiological substrates [1][2][3][4][5][6].…”

“…FAP degrades many bioactive peptides [1]. Neuropeptide Y (NPY) and fibroblast growth factor-21 (FGF-21) are physiological substrates [1][2][3][4][5][6]. FAP expression is very low in normal adult tissues [7,8] but elevated in cirrhosis [8,9] and non-alcoholic steatohepatitis (NASH) [10], and greatly upregulated in activated fibroblasts at sites of tissue remodeling [9].…”

“…Because Val-boro-Pro is non-selective, those effects could be due to inhibition of other DPPs including DPP4, and so investigations using FAP-selective approaches are needed. FAP cleaves several hormones [3,19] and rapidly inactivates FGF-21 in human and increases FGF-21 degradation in mouse [1,5,6,20]. FGF-21 improves glucose and insulin homeostasis and energy metabolism in non-alcoholic fatty liver disease (NAFLD).…”