Janko Kos

Neurite growth is regulated by trophic support and the extracellular matrix (ECM). γ-Enolase, a neuron-specific enolase isoform, promotes neurite outgrowth through neurotrophic-like activity, but the contribution of ECM engagement and integrin signaling remains unclear. Here, we examined the role of laminin, collagen, and poly-L-lysine in γ-enolase peptide-induced neuritogenesis in neuroblastoma SH-SY5Y and pheochromocytoma PC12 cells. Treatment with a synthetic C-terminal γ-enolase peptide (γ-Eno) rapidly induced neurite outgrowth and actin remodeling, with laminin providing the strongest enhancement, particularly in SH-SY5Y cells. γ-Eno increased surface expression of β1 integrin and, to a lesser extent, α1 integrin, alongside a stronger neurite response on laminin. In laminin-coated cells, actin remodeling was evident within 3 h, followed by increased neurite formation at 24 h and significant neurite elongation at 48 h. Mechanistically, γ-Eno induced focal adhesion kinase (FAK) phosphorylation, which was significantly increased in both cell types on laminin and collagen. Extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation was cell type- and ECM-dependent, whereas Akt phosphorylation increased significantly in SH-SY5Y cells but did not change markedly in PC12 cells. Integrin blockade with GRGDS attenuated γ-Eno-induced neurite outgrowth, MAP2 expression, and FAK phosphorylation. GRGDS also reduced Akt phosphorylation in SH-SY5Y cells and attenuated ERK1/2 phosphorylation in PC12 cells, supporting cell type-specific downstream signaling. These findings show that laminin-mediated integrin signaling enhances γ-enolase-induced neurite outgrowth and is associated with integrin-dependent FAK activation, with ERK1/2 and Akt contributing in a context-dependent manner.

Glial cells, namely microglia, astrocytes, and oligodendrocytes, play crucial roles in maintaining homeostasis in the central nervous system and orchestrating responses to injury, infection, and disease. Among the molecular regulators of glial function, cysteine cathepsins have emerged as key modulators of both physiological and pathological processes. These lysosomal peptidases are traditionally known for their housekeeping roles in protein degradation; however, accumulating evidence highlights their broader involvement in antigen presentation, microglial and astrocyte reactivity, inflammatory signalling, apoptosis, and myelination. Under normal conditions, cysteine cathepsins support essential functions in the central nervous system, including immune surveillance and tissue remodelling. Conversely, their dysregulation, characterized by overexpression, increased enzymatic activity, or mislocalization, can promote neuroinflammation and neurodegeneration, contributing to the pathogenesis of disorders such as Alzheimer’s disease and multiple sclerosis. This review provides a comprehensive synthesis specifically focused on the diverse roles of cysteine cathepsins across major glial cell types, systematically summarizing current knowledge in microglia, astrocytes, and oligodendrocytes. We emphasize their cell type-specific, context-dependent, protective, and deleterious functions. Furthermore, we discuss mechanistic links between cysteine cathepsin activity and neurodegenerative processes and evaluate the therapeutic potential and current limitations of selectively targeting glial cysteine cathepsins. A deeper understanding of the context-dependent dual roles of these enzymes in brain physiology and pathology is critical for designing targeted interventions that could mitigate neuroinflammation and neurodegeneration. Graphical Abstract

Pancreatic cancer remains one of the most lethal malignancies worldwide, with pancreatic ductal adenocarcinoma accounting for the vast majority of cases and characterized by extensive desmoplasia, immune exclusion, and resistance to systemic therapies. Increasing evidence implicates lysosomal cathepsins as important regulators of these defining features of pancreatic tumor biology. Cathepsin-dependent proteolysis and lysosome-associated signaling pathways contribute to extracellular matrix remodeling, regulate immune cell trafficking, and influence antigen processing and presentation. Beyond their classical degradative functions, cathepsins participate in stress-adaptive cellular programs linked to autophagy, metabolic regulation, and proteostasis, supporting tumor cell survival under hypoxic, nutrient-limited, and therapy-induced stress conditions. Within the tumor microenvironment, dysregulated cathepsin activity promotes immune evasion by reshaping cytokine networks, impairing effective antigen presentation, and reinforcing physical and functional barriers to cytotoxic T-cell infiltration. Collectively, these mechanisms position the lysosome–cathepsin system as a central regulator of proteolytic remodeling, immune exclusion, and adaptive therapy resistance in pancreatic cancer, highlighting its potential relevance for emerging combinatorial therapeutic strategies.

Pancreatic cancer remains one of the most lethal malignancies worldwide, with pancreatic ductal adenocarcinoma accounting for the vast majority of cases and characterized by extensive desmoplasia, immune exclusion, and resistance to systemic therapies. Increasing evidence implicates lysosomal cathepsins as important regulators of these defining features of pancreatic tumor biology. Cathepsin-dependent proteolysis and lysosome-associated signaling pathways contribute to extracellular matrix remodeling, regulate immune cell trafficking, and influence antigen processing and presentation. Beyond their classical degradative functions, cathepsins participate in stress-adaptive cellular programs linked to autophagy, metabolic regulation, and proteostasis, supporting tumor cell survival under hypoxic, nutrient-limited, and therapy-induced stress conditions. Within the tumor microenvironment, dysregulated cathepsin activity promotes immune evasion by reshaping cytokine networks, impairing effective antigen presentation, and reinforcing physical and functional barriers to cytotoxic T-cell infiltration. Collectively, these mechanisms position the lysosome–cathepsin system as a central regulator of proteolytic remodeling, immune exclusion, and adaptive therapy resistance in pancreatic cancer, highlighting its potential relevance for emerging combinatorial therapeutic strategies.

Neuronal differentiation into specific subtypes is crucial for nervous system development and function, guided by neurotrophic factors. γ-Enolase, a neuron-specific glycolytic enzyme, exhibits neurotrophic-like properties and supports neuronal differentiation; however, its role in specific neuronal subtypes remains unknown. Here, we investigate the role of γ-enolase in differentiation dopaminergic-, cholinergic-, and adrenergic-like neuronal cells. Our results demonstrate that γ-enolase expression is significantly upregulated in differentiated cells, with the highest expression observed in cholinergic-like neurons. Full-length γ-enolase, compared to its truncated form, promoted enhanced neurite outgrowth and increased β-tubulin, a cytoskeletal marker. Conversely, silencing endogenous γ-enolase significantly reduced neurite length, confirming its essential role in driving neuronal morphological maturation. Furthermore, a γ-enolase-derived peptide corresponding to the active C-terminus of γ-enolase significantly promoted neurite outgrowth and increased β-tubulin expression, particularly in cholinergic-like neuronal cells. Notably, γ-enolase activity is regulated by cathepsin X, a lysosomal peptidase that cleaves γ-enolase at its C-terminus, reducing its neurotrophic effects. Confocal microscopy revealed increased co-localization of γ-enolase and cathepsin X in differentiated neuronal cells, emphasizing their interaction in cholinergic-like neurons. Inhibiting cathepsin X preserved active γ-enolase, promoted neuronal differentiation, and altered cytoskeletal marker expression. These findings suggest an important role for γ-enolase in cholinergic-like neuronal cells and propose cathepsin X as a regulatory modulator of γ-enolase activity, suggesting novel therapeutic strategies for neuroregeneration.

A significant amount of data about the different pharmacological activities of the established antimicrobial compound nitroxoline (8-hydroxy-5-nitroquinoline) is available in the scientific literature. On the other hand, its regioisomer 8-hydroxy-6-nitroquinoline was never characterised biochemically and the same also applies to their 1,2,3,4-tetrahydroquinoline analogues. Herein, we determined the influence of pyridine ring saturation and the position of the nitro group on various biochemical characteristics of compounds, such as metal-chelating properties, inhibition of methionine aminopeptidases (MetAPs) from Mycobacterium tuberculosis and human MetAP2, as well as antibacterial activities on Escherichia coli , Staphylococcus aureus , and Mycobacterium smegmatis . In addition, inhibition of endopeptidase and exopeptidase activities of cathepsin B was determined, together with the ability of new nitroxo-line analogues to reduce intracellular collagen IV degradation. Substantially different biological activities were observed for the 6-nitro regioisomer of nitroxoline, as well as for both of their partially saturated counterparts.

Enolase is well-known for its role in glycolysis but also plays other roles in the central nervous system, including neuronal survival, differentiation, and axonal regeneration. Here, we investigated α- and γ-enolase expression patterns and their association with cathepsin X in distinct SH-SY5Y cell phenotypes. Enriched substrate-adherent S-type cells are characterized by large, flat morphology with extensive cytoplasm and higher expression of vimentin, while neuroblastic N-type are recognized by neurite extensions and higher expression of B-cell lymphoma 2 (Bcl-2) and growth-associated protein-43. We demonstrated that γ-enolase expression was specific to N-type cells, whereas α-enolase expression was not phenotype-specific. Moreover, a shift from ubiquitously expressed α-enolase to neuron-specific γ-enolase was observed during the enrichment and differentiation. Additionally, cathepsin X exhibited higher proteolytic activity in S-type cells. Inhibition of cathepsin X with AMS36 promoted differentiated cell morphology and increased expression of the active form of γ-enolase. Furthermore, AMS36 altered the expression of vimentin and Bcl-2, indicating a regulatory role in neuronal differentiation. Furthermore, AMS36 activated extracellular signal-regulated kinase 1/2 in N-type cells and enhanced the association between γ-enolase and tyrosine receptor kinase in both, suggesting a link between cathepsin X/γ-enolase and the key signaling pathways of differentiation. Our findings underscore the multifaceted role of enolase isoforms in SH-SY5Y cell differentiation, with α-enolase and γ-enolase showing distinct expression patterns in S- and N-type cells. The expression and activity of cathepsin X in S-type cells, along with its regulatory impact on γ-enolase in N-type cells, highlight the importance of these proteins in neuronal differentiation. Graphical The roles of α-enolase, γ-enolase, and cathepsin X in enriched and differentiated SH-SY5Y cell populations. The enrichment and differentiation of SH-SY5Y cells resulted in two distinct cell phenotypes: S-type and N-type cells. S-type cells were characterized by an epithelial-like morphology, the presence of vimentin, lower γ-enolase expression, and higher cathepsin X expression. N-type cells were characterized by a neuron-like morphology, GAP-43 and Bcl-2 expression, higher γ-enolase expression, and lower cathepsin X expression. Both phenotypes expressed α-enolase. The cathepsin X inhibitor AMS36 promoted SH-SY5Y cell differentiation and enrichment into S- and N-type cells. AMS36-treated S-type cells exhibited decreased vimentin levels and increased active γ-enolase levels, indicating enhanced differentiation. AMS36-treated N-type cells exhibited decreased Bcl-2 levels, indicating further differentiation. These results highlight the differential protein expression and activity between S- and N-type cells. Furthermore, they highlight the modulatory effects of AMS36, emphasizing its potential role in promoting differentiation and altering protein expression profiles.

Cystatin F, a cysteine peptidase inhibitor, is a potent modulator of NK cytotoxicity. By inhibiting granule-mediated cytotoxicity pathway, cystatin F induces formation of non-functional NK cell stage, called split-anergy. We show that N-glycosylation determines the localization and cellular function of cystatin F. Cystatin F mostly exhibited high-mannose glycosylation in U-937 cells, both high-mannose and complex glycosylation in NK-92 and primary NKs, and predominantly complex glycosylation in super-charged NKs. Manipulating N-glycosylation with kifunensine increased high-mannose glycosylation of cystatin F and lysosome localisation, which decreased cathepsin C activity and reduced NK cytotoxicity. Mannose-6-phosphate could significantly reduce the internalization of extracellular cystatin F. By comparing NK cells with different cytotoxic potentials, we found that high-mannose cystatin F was strongly associated with lysosomes and cathepsin C in NK-92 cell line. In contrast, in highly cytotoxic super-charged NKs, cystatin F with complex glycosylation was associated with the secretory pathway and less prone to inhibit cathepsin C. Modulating glycosylation to alter cystatin F localisation could increase the cytotoxicity of NK cells, thereby enhancing their therapeutic potential for treating cancer patients. Graphical abstract