Fibroblast Growth Factor 23 (FGF23) leads to endolysosomal routing of the renal phosphate co-transporters NaPi-IIa and NaPi-IIc in vivo

The sodium-dependent phosphate co-transporters NaPi-IIa and NaPi-IIc located at the brush border membrane of renal proximal tubules are regulated by numerous factors, including fibroblast growth factor 23 (FGF23). FGF23 downregulates NaPi-IIa and NaPi-IIc abundance after activating a signaling pathway involving phosphorylation of the extracellular signal-regulated protein kinase (phospho-ERK1/2). FGF23 also downregulates the expression of renal 1-α-hydroxylase (Cyp27b1) and upregulates 24-hydroxylase (Cyp24a1), thus reducing plasma calcitriol levels. Here, we examined the time course of the FGF23-induced internalization of NaPi-IIa and NaPi-IIc and their intracellular pathway towards degradation in vivo. Mice were injected intraperitoneally with recombinant human FGF23 (rh-FGF23) in the absence (biochemical analysis) or presence (immunohistochemistry) of leupeptin, an inhibitor of lysosomal proteases. Phosphorylation of ERK1/2 was enhanced 60 minutes after rh-FGF23 administration, and increased phosphorylation was still detected 480 minutes post-injection. Co-localization of phospho-ERK1/2 with NaPi-IIa was seen at 60, 120 and partly at 480 minutes. The abundance of both co-transporters was reduced 240 minutes after rh-FGF23 administration, with a further reduction at 480 minutes. NaPi-IIa and NaPi-IIc were found to co-localize with clathrin and early endosomal antigen 1 (EEA1) as early as 120 minutes after rh-FGF23 injection. Both co-transporters partially co-localized with cathepsin B and Lamp1, markers of lysosomes, 120 minutes after rh-FGF23 injection. Thus, NaPi-IIa and NaPi-IIc are internalized within 2 hours upon rh-FGF23 injection. Both co-transporters share the pathway of clathrin-mediated endocytosis that leads first to early endosomes, finally resulting in trafficking towards the lysosome as early as 120 minutes after rh-FGF23 administration.

Processing of progranulin into granulins involves multiple lysosomal proteases and is affected in frontotemporal lobar degeneration

Background 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. Results 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. Conclusions 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.

Cathepsin D—Managing the Delicate Balance

Lysosomal proteases play a crucial role in maintaining cell homeostasis. Human cathepsin D manages protein turnover degrading misfolded and aggregated proteins and favors apoptosis in the case of proteostasis disruption. However, when cathepsin D regulation is affected, it can contribute to numerous disorders. The down-regulation of human cathepsin D is associated with neurodegenerative disorders, such as neuronal ceroid lipofuscinosis. On the other hand, its excessive levels outside lysosomes and the cell membrane lead to tumor growth, migration, invasion and angiogenesis. Therefore, targeting cathepsin D could provide significant diagnostic benefits and new avenues of therapy. Herein, we provide a brief overview of cathepsin D structure, regulation, function, and its role in the progression of many diseases and the therapeutic potentialities of natural and synthetic inhibitors and activators of this protease.

Cathepsin B and D deficiency in the mouse pancreas induces impaired autophagy and chronic pancreatitis

The major lysosomal proteases, Cathepsin B (CTSB), Cathepsin D (CTSD) and Cathepsin L (CTSL), are implicated in autophagic activity. To investigate the role of each cathepsin in the exocrine pancreas, we generated mice in which the pancreas was specifically deficient in Ctsb, Ctsd and Ctsl. Each of these gene knockout (KO) and Ctsb;Ctsl and Ctsd;Ctsl double-knockout (DKO) mice were almost normal. However, we found cytoplasmic degeneration in the pancreatic acinar cells of Ctsb;Ctsd DKO mice, similar to autophagy related 5 (Atg5) KO mice. LC3 and p62 (autophagy markers) showed remarkable accumulation and the numbers of autophagosomes and autolysosomes were increased in the pancreatic acinar cells of Ctsb;Ctsd DKO mice. Moreover, these Ctsb;Ctsd DKO mice also developed chronic pancreatitis (CP). Thus, we conclude that both Ctsb and Ctsd deficiency caused impaired autophagy in the pancreatic acinar cells, and induced CP in mice.

FUNCTIONAL CHANGES IN THE CONCENTRATION OF TOTAL PROTEIN IN RESIDENTS OF THE KYZYLORDA REGION

Taking into account the ever-increasing role of prevention in modern conditions, a comprehensive understanding of the morph physiological and chronobiological organization of human life is necessary, which is most optimal for living in specific environmental conditions, in other words, the conditions for the formation of population health and its pathological deviations due to factors that exist in the very organism, as well as acting on it from the outside. The process of cleansing the body of denatured, aged proteins occurs in many organs, primarily in the liver. Degradation processes in a cell can both recognize proteins to be degraded and begin degradation, but these processes must be selective, since there is significant heterogeneity in the rates of degradation of various proteins in one cell. Proteases are usually required for the implementation of catabolic processes, and apparently, lysosomal and extra-lysosomal proteases are involved in the catabolism of cellular proteins. The concentration of total protein and its fractions in the blood plasma in people living in various districts of the Kyzylorda region does not depend on the severity of the action of extreme factors characteristic of the Aral Sea zone.

Processing of progranulin into granulins involves multiple lysosomal proteases and is affected in frontotemporal lobar degeneration

Background - 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. Results - 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 show increased PGRN processing to granulin F and an increased activity of AEP, in a region-specific manner. Conclusions - 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.

Processing of progranulin into granulins involves multiple lysosomal proteases and is affected in frontotemporal lobar degeneration

Background - 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 at a range of pH setpoints. Results - 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 variable, 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 show increased PGRN processing to granulin F, correlating with increased activity of AEP, in a region-specific manner. Conclusions - This study demonstrates that multiple lysosomal proteases may work in concert to liberate granulins and implicates both AEP and granulin F in the neurobiology of FTLD-TDP-Pgrn. Modulating progranulin cleavage may represent a new strategy to modulate PGRN and granulin levels in disease.

Processing of progranulin into granulins involves multiple lysosomal proteases and is affected in frontotemporal lobar degeneration

Background: 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 at a range of pH setpoints.Results: 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 variable, 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 show increased PGRN processing to granulin F, correlating with increased activity of AEP, in a region-specific manner. Conclusions: This study demonstrates that multiple lysosomal proteases may work in concert to liberate granulins and implicates both AEP and granulin F in the neurobiology of FTLD-TDP-Pgrn. Modulating progranulin cleavage may represent a new strategy to modulate PGRN and granulin levels in disease.

The Ins and Outs of Cathepsins: Physiological Function and Role in Disease Management

Cathepsins are the most abundant lysosomal proteases that are mainly found in acidicendo/lysosomal compartments where they play a vital role in intracellular protein degradation,energy metabolism, and immune responses among a host of other functions. The discovery thatcathepsins are secreted and remain functionally active outside of the lysosome has caused a paradigmshift. Contemporary research has unraveled many versatile functions of cathepsins in extralysosomallocations including cytosol and extracellular space. Nevertheless, extracellular cathepsins are majorlyupregulated in pathological states and are implicated in a wide range of diseases including cancerand cardiovascular diseases. Taking advantage of the dierential expression of the cathepsinsduring pathological conditions, much research is focused on using cathepsins as diagnostic markersand therapeutic targets. A tailored therapeutic approach using selective cathepsin inhibitors isconstantly emerging to be safe and ecient. Moreover, recent development of proteomic-basedapproaches for the identification of novel physiological substrates oers a major opportunity tounderstand the mechanism of cathepsin action. In this review, we summarize the available evidenceregarding the role of cathepsins in health and disease, discuss their potential as biomarkers ofdisease progression, and shed light on the potential of extracellular cathepsin inhibitors as safetherapeutic tools.