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A cellular feature of Parkinson’s disease is cytosolic accumulation and amyloid formation of α-synuclein (α-syn), implicating a misregulation or impairment of protein degradation pathways involving the proteasome and lysosome. Within lysosomes, cathepsin D (CtsD), an aspartyl protease, is suggested to be the main protease for α-syn clearance; however, the protease alone only generates amyloidogenic C terminal-truncated species (e.g., 1–94, 5–94), implying that other proteases and/or environmental factors are needed to facilitate degradation and to avoid α-syn aggregation in vivo. Using liquid chromatography–mass spectrometry, to our knowledge, we report the first peptide cleavage map of the lysosomal degradation process of α-syn. Studies of purified mouse brain and liver lysosomal extracts and individual human cathepsins demonstrate a direct involvement of cysteine cathepsin B (CtsB) and L (CtsL). Both CtsB and CtsL cleave α-syn within its amyloid region and circumvent fibril formation. For CtsD, only in the presence of anionic phospholipids can this protease cleave throughout the α-syn sequence, suggesting that phospholipids are crucial for its activity. Taken together, an interplay exists between α-syn conformation and cathepsin activity with CtsL as the most efficient under the conditions examined. Notably, we discovered that CtsL efficiently degrades α-syn amyloid fibrils, which by definition are resistant to broad spectrum proteases. This work implicates CtsB and CtsL as essential in α-syn lysosomal degradation, establishing groundwork to explore mechanisms to enhance their cellular activity and levels as a potential strategy for clearance of α-syn.

Enniatin B (ENN B) and Beauvericin (BEA) are cyclohexadepsipeptides that can be isolated from Fusarium and Beauveria bassiana, respectively. Both compounds are cytotoxic and ionophoric. In the present study, the mechanism of cell death induced by these compounds was investigated. Epidermal carcinoma-derived cell line KB-3-1 cells were treated with different concentrations of these compounds. The extracellular secretion of cathepsin B increased in a concentration-dependent manner, and the lysosomal staining by lysotracker red was reduced upon the treatment with any of the compounds. However, the extracellular secretion of cathepsin L and cathepsin D were not affected. Inhibition of cathepsin B with specific inhibitor CA074 significantly reduced the cytotoxic effect of both compounds, while inhibition of cathepsin D or cathepsin L did not influence the cytotoxic activities of both compounds. In vitro labelling of lysosomal cysteine cathepsins with Ethyl (2S, 3S)-epoxysuccinate-Leu-Tyr-Acp-Lys (Biotin)-NH2 (DCG04) was not affected in case of cathepsin L upon the treatment with both compounds, while it was significantly reduced in case of cathepsin B. In conclusion, ENN B and BEA increase lysosomal Ph, which inhibits delivery of cathepsin B from Golgi to lysosomes, thereby inducing cathepsin B release in cytosol, which activates caspases and hence the apoptotic pathway.

Heterozygous loss-of-function mutations in the progranulin ( GRN ) gene and the resulting reduction of GRN levels is a common genetic cause for frontotemporal lobar degeneration (FTLD) with accumulation of TAR DNA-binding protein (TDP)-43. Recently, it has been shown that a complete GRN deficiency due to a homozygous GRN loss-of-function mutation causes neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disorder. These findings suggest that lysosomal dysfunction may also contribute to some extent to FTLD. Indeed, Grn (−/−) mice recapitulate not only pathobiochemical features of GRN-associated FTLD-TDP (FTLD-TDP/GRN), but also those which are characteristic for NCL and lysosomal impairment. In Grn (−/−) mice the lysosomal proteins cathepsin D (CTSD), LAMP (lysosomal-associated membrane protein) 1 and the NCL storage components saposin D and subunit c of mitochondrial ATP synthase (SCMAS) were all found to be elevated. Moreover, these mice display increased levels of transmembrane protein (TMEM) 106B, a lysosomal protein known as a risk factor for FTLD-TDP pathology. In line with a potential pathological overlap of FTLD and NCL, Ctsd (−/−) mice, a model for NCL, show elevated levels of the FTLD-associated proteins GRN and TMEM106B. In addition, pathologically phosphorylated TDP-43 occurs in Ctsd (−/−) mice to a similar extent as in Grn (−/−) mice. Consistent with these findings, some NCL patients accumulate pathologically phosphorylated TDP-43 within their brains. Based on these observations, we searched for pathological marker proteins, which are characteristic for NCL or lysosomal impairment in brains of FTLD-TDP/GRN patients. Strikingly, saposin D, SCMAS as well as the lysosomal proteins CTSD and LAMP1/2 are all elevated in patients with FTLD-TDP/GRN. Thus, our findings suggest that lysosomal storage disorders and GRN-associated FTLD may share common features.

Mucins are functionally implicated in a range of human pathologies, including cystic fibrosis, influenza, bacterial endocarditis, gut dysbiosis, and cancer. These observations have motivated the study of mucin biosynthesis as well as the development of strategies for inhibition of mucin glycosylation. Mammalian pathways for mucin catabolism, however, have remained underexplored. The canonical view, derived from analysis of N-glycoproteins in human lysosomal storage disorders, is that glycan degradation and proteolysis occur sequentially. Here, we challenge this view by providing genetic and biochemical evidence supporting mammalian proteolysis of heavily O-glycosylated mucin domains without prior deglycosylation. Using activity screening coupled with mass spectrometry, we ascribed mucin-degrading activity in murine liver to the lysosomal protease cathepsin D. Glycoproteomics of substrates digested with purified human liver lysosomal cathepsin D provided direct evidence for proteolysis within densely O-glycosylated domains. Finally, knockout of cathepsin D in a murine model of the human lysosomal storage disorder neuronal ceroid lipofuscinosis 10 resulted in accumulation of mucins in liver-resident macrophages. Our findings imply that mucindegrading activity is a component of endogenous pathways for glycoprotein catabolism in mammalian tissues.

The beta‐site amyloid precursor protein cleaving enzyme‐1 (BACE‐1) initiates the generation of amyloid‐β (Aβ), and the amyloid cascade leading to amyloid plaque deposition, neurodegeneration, and dementia in Alzheimer's disease (AD). Clinical failures of anti‐Aβ therapies in dementia stages suggest that treatment has to start in the early, asymptomatic disease states. The BACE‐1 inhibitor CNP520 has a selectivity, pharmacodynamics, and distribution profile suitable for AD prevention studies. CNP520 reduced brain and cerebrospinal fluid (CSF) Aβ in rats and dogs, and Aβ plaque deposition in APP‐transgenic mice. Animal toxicology studies of CNP520 demonstrated sufficient safety margins, with no signs of hair depigmentation, retina degeneration, liver toxicity, or cardiovascular effects. In healthy adults ≥ 60 years old, treatment with CNP520 was safe and well tolerated and resulted in robust and dose‐dependent Aβ reduction in the cerebrospinal fluid. Thus, long‐term, pivotal studies with CNP520 have been initiated in the Generation Program. Synopsis Alzheimer's disease (AD) is a chronic neurodegenerative disorder with increasing incidence in the aging societies, but without any disease‐modifying treatment. Deposition of toxic forms of the protein Aβ in the brain is pathologic. Treatment with a BACE‐1 inhibitor may prevent Aβ deposition. Recent BACE inhibitor clinical trials in patients at early or mild‐to‐moderate disease stage have failed, indicating that treatment needs to start earlier, before the onset of clinical symptoms. BACE inhibitor CNP520 was designed to meet the requirements of prevention treatment. CNP520 in preclinical models showed acute and chronic Aβ reduction, and a favorable safety profile. CNP520 is safe and well tolerated in humans, and dose‐dependently reduced Aβ in cerebrospinal fluid. Prevention studies Generation I and II are underway in patients at enhanced risk to develop symptoms of AD. Graphical Abstract Alzheimer's disease (AD) is a chronic neurodegenerative disorder with increasing incidence in the aging societies, but without any disease‐modifying treatment. Deposition of toxic forms of the protein Aβ in the brain is pathologic. Treatment with a BACE‐1 inhibitor may prevent Aβ deposition.

Colorectal cancer (CRC) is among the most prevalent and deadly malignancies worldwide. Despite advancements in screening and treatment, its aggressive progression and tendency to metastasize remain major challenges. Biomarkers such as cathepsins B and D, actin isoforms, and cysteine protease inhibitors may influence tumor invasion and metastasis. However, little is known about their spatial distribution in tumor versus surrounding tissue. This study aimed to evaluate the location-dependent expression of selected biomarkers in CRC tissue to better understand their role in cancer progression. Tissue samples were obtained intraoperatively from 37 CRC patients at three locations: the tumor center, and 2 cm and 5 cm from the tumor margin. The activity and concentrations of cathepsins B and D, anti-papain activity, and actin fractions (globular [G-], filamentous [F-], and total actin [T-actin]) were measured using biochemical and spectrophotometric assays. Statistical analyses included ANOVA, MANOVA, and non-parametric tests, with significance set at p < 0.05. Cathepsin B activity was significantly elevated at the tumor center and decreased with distance from the tumor (p < 0.001). F-actin and T-actin levels followed a similar pattern, with significantly higher values near the tumor core (p < 0.05). Differences in G-actin were less pronounced. No significant spatial variation was found for cathepsin D, or anti-papain activity. The G-actin/T-actin and F-actin/G-actin ratios revealed significant shifts in actin polymerization states depending on the distance from the tumor. This study demonstrates spatial heterogeneity in the expression of key biomarkers in CRC tissues. Elevated levels of cathepsin B and altered actin dynamics in tumor regions suggest their involvement in local invasion and progression.

We aim to investigate the mechanisms underlying the beneficial effects of exercise rehabilitation (ER) and/or astragaloside (AST) in counteracting amyloid-beta (Aβ) pathology. Aβ oligomers were microinjected into the bilateral ventricles to induce Aβ neuropathology in rats. Neurobehavioral functions were evaluated. Cortical and hippocampal expressions of both BDNF/TrkB and cathepsin D were determined by the western blotting method. The rat primary cultured cortical neurons were incubated with BDNF and/or AST and ANA12 followed by exposure to aggregated Aβ for 24 h. In vivo results showed that ER and/or AST reversed neurobehavioral disorders, downregulation of cortical and hippocampal expression of both BDNF/TrkB and cathepsin D, neural pathology, Aβ accumulation, and altered microglial polarization caused by Aβ. In vitro studies also confirmed that topical application of BDNF and/or AST reversed the Aβ-induced cytotoxicity, apoptosis, mitochondrial distress, and synaptotoxicity and decreased expression of p-TrkB, p-Akt, p-GSK3β, and β-catenin in rat cortical neurons. The beneficial effects of combined ER (or BDNF) and AST therapy in vivo and in vitro were superior to ER (or BDNF) or AST alone. Furthermore, we observed that any gains from ER (or BDNF) and/or AST could be significantly eliminated by ANA-12, a potent BDNF/TrkB antagonist. These results indicate that whereas ER (or BDNF) and/or AST attenuate Aβ pathology by reversing BDNF/TrkB signaling deficits and mitochondrial dysfunction, combining these two potentiates each other’s therapeutic effects. In particular, AST can be an alternative therapy to replace ER.

Purpose Cathepsin D is a proteolytic enzyme that is normally localized in the lysosomes and is involved in the malignant progression of breast cancer. There are conflicting results regarding Cathepsin D significance as prognostic and predictor marker in breast cancer. This study aimed to evaluate the expression and prognostic significance of Cathepsin D in early-stage breast cancer. Methods Expression of Cathepsin D was assessed by immunohistochemical staining of tissue microarrays, in a large well-characterized series of early-stage operable breast cancer ( n  = 954) from Nottingham Primary Breast Carcinoma Series between the period of 1988 and 1998 who underwent primary surgery. Correlation of Cathepsin D expression with clinicopathological parameters and prognosis was evaluated. Results Cathepsin D expression was positive in 71.2% (679/954) of breast cancer tumours. Positive expression of Cathepsin D was significantly associated with high histological grade ( p  = 0.007), pleomorphism ( p  = 0.002), poor Nottingham Prognostic Index (NPI) score ( p  < 0.002), recurrence ( p  = 0.005 ) and distant metastasis ( p  < 0.0001). Kaplan–Meier analysis showed that Cathepsin D expression was significantly associated with shorter breast cancer-specific survival ( p  = 0.001), higher risk of recurrence ( p  = 0.001) and distant metastasis ( p  < 0.0001). ER-positive tumours expressing Cathepsin D and treated with tamoxifen demonstrated a significantly higher risk of distant metastasis. Conclusion Cathepsin D expression significantly predicts poor prognosis in breast cancer and is associated with variables of poor prognosis and shorter outcome. The strong association of Cathepsin D with aggressive tumour characteristics and poor outcomes warrants further research of its potential as a therapeutic target The results also suggest a possible interaction between Cathepsin D and tamoxifen therapy in ER-positive breast cancer which needs further investigation to elucidate the underlying mechanisms.

This study investigates the role of Cathepsin D (CTSD) in diabetic vascular complications, particularly its impact on the phenotypic transformation of vascular smooth muscle cells (VSMCs) induced by advanced glycation end-products (AGEs), and explores its potential molecular mechanisms. CTSD was overexpressed in VSMCs using lentiviral vectors. Various methods, including CCK-8, immunofluorescence, SA-β-Gal staining, EdU assay, scratch assay, cell cycle analysis, and Western blotting, were employed to assess VSMC viability, proliferation, migration, senescence, and apoptosis. Additionally, transcriptomic and metabolomic analyses were conducted to investigate the molecular mechanisms underlying CTSD overexpression in VSMCs. AGEs treatment significantly inhibited CTSD expression in VSMCs, leading to reduced cell viability, enhanced proliferation and migration, increased senescence, and apoptosis. In contrast, overexpression of CTSD effectively inhibited AGEs-induced VSMCs proliferation, migration, senescence, and apoptosis. Combined transcriptomic and metabolomic analyses suggested that CTSD may affect VSMCs phenotypic transformation by inhibiting the glycolysis pathway. This study highlights the critical role of CTSD in the phenotypic transformation of VSMCs induced by AGEs and provides a new perspective for cardiovascular and cerebrovascular disease treatment. CTSD may emerge as a novel therapeutic target, though its specific molecular mechanisms and clinical application prospects in VSMCs phenotypic transformation require further investigation.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is one of the most important citrus pests. ACP is the vector of the phloem-limited bacteria Candidatus Liberibacter americanus and Candidatus Liberibacter asiaticus, the causal agents of the devastating citrus disease huanglongbing (HLB). The management of HLB is based on the use of healthy young plants, eradication of infected plants and chemical control of the vector. RNA interference (RNAi) has proven to be a promising tool to control pests and explore gene functions. Recently, studies have reported that target mRNA knockdown in many insects can be induced through feeding with double-stranded RNA (dsRNA). In the current study, we targeted the cathepsin D, chitin synthase and inhibitor of apoptosis genes of adult and nymph ACP by feeding artificial diets mixed with dsRNAs and Murraya paniculata leaves placed in dsRNAs solutions, respectively. Adult ACP mortality was positively correlated with the amount of dsRNA used. Both nymphs and adult ACP fed dsRNAs exhibited significantly increased mortality over time compared with that of the controls. Moreover, qRT-PCR analysis confirmed the dsRNA-mediated RNAi effects on target mRNAs. These results showed that RNAi can be a powerful tool for gene function studies in ACP and perhaps for HLB control.