Progranulin loss-of-function mutations are linked to frontotemporal lobar degeneration with TDP-43 positive inclusions (FTLD-TDP-Pgrn). Progranulin (PGRN) is an intracellular and secreted pro-protein that is proteolytically cleaved into individual granulin peptides, which are increasingly thought to contribute to FTLD-TDP-Pgrn disease pathophysiology. Intracellular PGRN is processed into granulins in the endo-lysosomal compartments. Therefore, to better understand the conversion of intracellular PGRN into granulins, we systematically tested the ability of different classes of endo-lysosomal proteases to process PGRN at a range of pH setpoints. In vitro cleavage assays identified multiple enzymes that can process human PGRN into multi- and single-granulin fragments in a pH-dependent manner. We confirmed the role of cathepsin B and cathepsin L in PGRN processing and showed that these and several previously unidentified lysosomal proteases (cathepsins E, G, K, S and V) are able to process PGRN in distinctive, pH-dependent manners. In addition, we have demonstrated a new role for asparagine endopeptidase (AEP) in processing PGRN, with AEP having the unique ability to liberate granulin F from the pro-protein. Brain tissue from individuals with FTLD-TDP-Pgrn showed increased PGRN processing to granulin F and increased AEP activity in degenerating brain regions but not in regions unaffected by disease. This study demonstrates that multiple lysosomal proteases may work in concert to liberate multi-granulin fragments and granulins. It also implicates both AEP and granulin F in the neurobiology of FTLD-TDP-Pgrn. Modulating progranulin cleavage and granulin production may represent therapeutic strategies for FTLD-Pgrn and other progranulin-related diseases.

中文翻译：

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将颗粒蛋白前体加工成颗粒蛋白涉及多种溶酶体蛋白酶，并在额颞叶变性中受到影响

颗粒蛋白前体功能丧失突变与 TDP-43 阳性包涵体 (FTLD-TDP-Pgrn) 的额颞叶变性有关。颗粒蛋白前体 (PGRN) 是一种细胞内分泌的前蛋白，它被蛋白水解切割成单个颗粒蛋白肽，越来越多地认为这些肽有助于 FTLD-TDP-Pgrn 疾病的病理生理学。细胞内 PGRN 在内溶酶体区室中被加工成颗粒蛋白。因此，为了更好地了解细胞内 PGRN 向颗粒蛋白的转化，我们系统地测试了不同种类的内溶酶体蛋白酶在一系列 pH 设定值下处理 PGRN 的能力。体外切割试验鉴定了多种酶，这些酶可以以 pH 依赖性方式将人类 PGRN 加工成多颗粒和单颗粒蛋白片段。我们证实了组织蛋白酶 B 和组织蛋白酶 L 在 PGRN 加工中的作用，并表明这些和几种以前未鉴定的溶酶体蛋白酶（组织蛋白酶 E、G、K、S 和 V）能够以独特的 pH 依赖性方式加工 PGRN。此外，我们已经证明了天冬酰胺内肽酶 (AEP) 在加工 PGRN 中的新作用，AEP 具有从前蛋白中释放颗粒蛋白 F 的独特能力。来自 FTLD-TDP-Pgrn 个体的脑组织显示，PGRN 对颗粒蛋白 F 的加工增加，并且在退化的大脑区域中 AEP 活性增加，但在未受疾病影响的区域中没有。该研究表明，多种溶酶体蛋白酶可能协同作用以释放多颗粒蛋白片段和颗粒蛋白。它还暗示 AEP 和颗粒蛋白 F 在 FTLD-TDP-Pgrn 的神经生物学中。