Eleni Zingkou

The NerveRepack project is a European initiative that aims to develop biomimetic exoskeletons/exoprostheses for amputated or paralyzed leg patients that will receive and transmit signals to enable movements and sensations for the patient. To implement the project, it is fundamental to develop implantable neuronal electrodes that will allow bidirectional signaling between the sensors placed on the exoskeletons/exoprostheses and the nervous system. In this direction, two electrodes, plug and cuff, have been designed as integral parts of the final implantable device. The electrodes should comply with strict regulations to ensure their safe implantation in patients. The purpose of this study was to support the compliance of the implant platforms of certain key components with the ISO and ASTM standards that would be required for clinical applications. We have used an indirect method to assess the biocompatibility of the developed electrodes against neuronal cells, fibroblasts, and keratinocytes. Also, we assessed hemocompatibility, i.e., the potential of implantable electrodes to induce hemolysis or complement activation. Finally, the mutagenic/genotoxic potential was tested against the internationally recommended CHO cells. Both representative plug and cuff electrode components were found non-cytotoxic, non-mutagenic, and unable to induce hemolysis. Therefore, from the point of early evaluation of in vitro material and process biocompatibility, the selected implant platforms for the electrodes could be implanted in preclinical models to delineate their potential in vivo applications as neuronal interface with the biomimetic exoskeleton/exoprostheses.

Netherton syndrome (NS) is a rare, severe, and often life‐threatening disease for which current therapeutic approaches are limited and show variable effectiveness. NS is characterized by excessive epidermal desquamation that results in a highly defective epidermal barrier, constitutive skin inflammation, allergies, and hair abnormalities. NS develops due to loss‐of‐function mutations in the SPINK5 gene, which encodes the LEKTI inhibitor that regulates KLK proteases (KLK5, KLK6, KLK7, KLK13, and KLK14). These findings indicate that dysregulation of proteolytic networks underlies the extensive skin shedding and inflammation characteristic of NS. Spink5 ^−/− mice recapitulate the major features of the human disease but exhibit neonatal lethality. Several double‐ and triple‐knockout models have been generated to rescue the lethal NS phenotype, and have proved instrumental in studies aiming to elucidate the biological pathways involved in NS, and to identify and validate potential targets for drug development. These studies have established that inhibition of excessive KLK protease activity in LEKTI‐deficient epidermis can reverse the cutaneous manifestations of NS. In particular, ablation of KLK5 results in a marked therapeutic response, although KLK7 or TNFα must also be inhibited to rescue the most severe (lethal) form of NS. Murine models have also been essential in proving or disproving putative pathways and/or therapeutic targets proposed from in vitro studies or patient case studies. Collectively, these models have provided a deeper understanding of the epidermal proteolytic cascades involved in NS pathology and in normal skin renewal. Moreover, these models offer a platform in which disease‐specific candidate therapeutics can be tested and preclinically validated. © 2026 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Congenital ichthyoses, now grouped under the acronym EDD (Epidermal Differentiation Disorders), include nonsyndromic forms (nEDD) that may be caused by loss-of-function mutations in the CDSN gene encoding corneodesmosin (CDSN-nEDD, formerly Peeling skin syndrome type 1). It is characterized by skin peeling, inflammation, itching and food allergies, while no specific therapy is currently available. High levels of KLK5, the serine protease that initiates the desquamation cascade, are found in the epidermis of CDSN-nEDD patients. Thus, we hypothesized that KLK5 inhibition would alleviate the symptoms of CDSN-nEDD and could serve as a new pharmacological target. A human epidermal equivalent (HEE) model for CDSN-nEDD was developed using shRNA-mediated CDSN knockdown. This model was characterized and used to assess the role of KLK5 knockdown on CDSN-nEDD. Also, Klk5^−/− mice were crossed with Cdsn^epi−/− mice, the murine model of CDSN-nEDD, to examine in vivo the effect(s) of Klk5 deletion in CDSN-nEDD. Both models recapitulated the CDSN-nEDD desquamating phenotype. Elimination of KLK5 aggravated the CDSN-nEDD phenotype. Epidermal proteolysis was surprisingly elevated, while severe ultrastructural (corneo)desmosomal alterations increased epidermal barrier permeability and stratum corneum detachment was manifested. Based on these results, we concluded that targeting epidermal proteolysis with KLK5 ablation cannot compensate for the loss of corneodesmosin and rescue over-desquamation of the CDSN-nEDD. Possibly, in the absence of KLK5, other proteases take over which increases the severity of over-desquamation in CDSN-nEDD. The translational outcome is that over-desquamation may not always be rescued by eliminating epidermal proteolysis, but fine protease modulation is more likely required.

Stainless steel (SS) 316l constitutes a popular biomaterial with various applications as implants in cardiovascular and orthopedic surgery, as well as in dentistry. Nevertheless, its cytocompatibility against neuronal cells has not been investigated, a feature that is important for the construction of implants that require contact with neurons, e.g., neuronal electrodes. In addition, most cytocompatibility studies have focused on decorated or surface-modified SS 316l. On the other hand, SH-SY5Y cells are an established cellular model for cytocompatibility studies of potential biomaterials given their ability to differentiate into neuron-like cells. Here, we used retinoic-acid-differentiated SH-SY5Y cells and SH-SY5Y controls to investigate the cytocompatibility and biomimetics of uncoated SS 316l. The assessment of cytocompatibility was based on the determination of differentiation markers by immunofluorescence, RT-qPCR, and the neurite growth of these cells attached on SS 316l and standard tissue culture polystyrene (TCP) surfaces. Even though the neurite length was shorter in differentiated SH-SY5Y cells grown on SS 316l, no other significant changes were found. In conclusion, our results suggest that the uncoated SS 316l mimics a natural bio-surface and allows the adhesion, growth, and differentiation of SH-SY5Y cells. Therefore, this alloy can be directly applied in the emerging field of biomimetics, especially for the development of implants or devices that contact neurons.

Dear EditorsWe read with great interest the recent publication by Lee et al.,1 in which the important paper by Lovell et al.2 is presented as the first report of activity-based protein profiling (A...

Proteases are important enzymes in health and disease. Their activities are regulated at multiple levels. In fact, proteases are synthesized as inactive proenzymes (zymogens) that are activated by proteolytic removal of their pro-peptide sequence and can remain active or their activity can be attenuated by complex formation with specific endogenous inhibitors or by limited proteolysis or degradation. Consequently, quite often, only a fraction of the protease molecules is in the active/functional form, thus, the abundance of a protease is not always linearly proportional to the (patho)physiological function(s). Therefore, assays to determine the active forms of proteases are needed, not only in research but also in molecular diagnosis and therapy. Activity-based probes (ABPs) are chemical entities that bind covalently to the active enzyme/protease. ABPs carry a detection tag to enable localization and quantification of specific enzymatic/proteolytic activities with applications in molecular imaging and diagnosis. Moreover, ABPs act as suicide inhibitors of proteases, which can be exploited for delineation of the functional role(s) of a given protease in (patho) biological context and as potential therapeutics. In this sense, ABPs represent new theranostic agents. We outline recent developments pertaining to ABPs for proteases with potential therapeutic applications, with the aim to highlight their importance in theranostics.

The epidermis is the outer stratified epithelium of the skin, forming the physical barrier that is indispensable for homeostasis. Epidermal proteolysis, mainly but not exclusively executed by kallikrein‐related peptidases (KLKs), is tightly regulated to ensure maintenance of physiological skin renewal and an intact skin barrier. Perturbation of epidermal proteolytic networks is implicated in a wide array of rare and common skin pathologies of diverse genetic backgrounds. Recent studies of monogenic human skin diseases and newly developed animal models have revealed new mechanisms of regulation of proteolytic pathways in epidermal physiology and in disease states. These new data have challenged some accepted views, for example the role of matriptase in epidermal desquamation, which turned out to be restricted to mouse skin. The significance of PAR2 signaling in skin inflammation should also be reconsidered in the face of recent findings. Cumulatively, recent studies necessitate a sophisticated redefinition of the proteolytic and signaling pathways that operate in human skin. We elaborate how epidermal proteolysis is finely regulated at multiple levels, and in a spatial manner that has not been taken into consideration so far, in which specific proteases are confined to distinct epidermal sublayers. Of interest, transglutaminases have emerged as regulators of epidermal proteolysis and desquamation by spatially fixing endogenous protease inhibitors, constituting regulatory factors that were not recognized before. Furthermore, new evidence suggests a link between proteolysis and lipid metabolism. By synthesis of established notions and recent discoveries, we provide an up‐to‐date critical evaluation and synthesis of current knowledge and the extended complexity of proteolysis regulation and signaling pathways in skin. © 2022 The Pathological Society of Great Britain and Ireland.

ALS is a fatal untreatable disease involving degeneration of motor neurons. Μultiple causative genes encoding proteins with versatile functions have been identified indicating that diverse biological pathways lead to ALS. Chemical entities still represent a promising choice to delay ALS progression, attenuate symptoms and/or increase life expectancy, but also gene‐based and stem cell‐based therapies are in the process of development, and some are tested in clinical trials. Various compounds proved effective in transgenic models overexpressing distinct ALS causative genes unfortunately though, they showed no efficacy in clinical trials. Notably, while animal models provide a uniform genetic background for preclinical testing, ALS patients are not stratified, and the distinct genetic forms of ALS are treated as one group, which could explain the observed discrepancies between treating genetically homogeneous mice and quite heterogeneous patient cohorts. We suggest that chemical entity‐genotype correlation should be exploited to guide patient stratification for pharmacotherapy, that is administered drugs should be selected based on the ALS genetic background.

Netherton syndrome (NS) is a rare, severe type of ichthyosis, often lethal in neonates, for which there is no therapy. Spink5^−/− mice recapitulate major NS hallmarks and die homogeneously within 5 h from birth due to severe epidermal barrier defect leading to dehydration. Spink5^−/−Klk5^−/− mice survive neonatal lethality, indicating that KLK5 could be a drug target for NS. Nevertheless, after a week, these mice developed epidermal inflammation and signs of barrier defect leading to lethality. Here we tested whether anti-TNFα strategy in combination with anti-KLK5 could provide a long-term effective therapy for NS. Deletion of Tnfa in Spink5^−/− suppressed the inflammatory phenotype but did not rescue neonatal lethality of Spink5^−/− indicating that anti-TNFα therapy alone would not be sufficient to treat NS. Interestingly, in Spink5^−/−Klk5^−/−Tnfa^−/− mice, NS features were rescued, and mice lived normally for 16–18 months. For the first time, evidence is provided that a combination of anti-TNFα and anti-KLK5 therapeutics represents an effective therapeutic strategy for NS. Notably, anti-TNFα factors are marketed and used widely, while LMW KLK5 inhibitors are being developed.

The epidermis is a stratified epithelium that forms the barrier between the organism and its environment. It is mainly composed of keratinocytes at various stages of differentiation. The stratum corneum is the outermost layer of the epidermis and is formed of multiple layers of anucleated keratinocytes called corneocytes. We aim to highlight the roles of epidermal differentiation and proteolysis in skin diseases. Skin biopsies isolated from Spink5^-/- mice, the established model of Netherton syndrome (NS), and from patients with NS, seborrheic dermatitis (SD) and psoriasis, as well as healthy controls, were analyzed by histology and immunohistochemistry. Our results showed that NS, SD, and psoriasis are all characterized by abnormal epidermal differentiation, manifested by hyperplasia, hyperkeratosis, and parakeratosis. At the molecular level, abnormal differentiation is accompanied by increased expression of involucrin and decreased expression of loricrin in NS and psoriasis. Increased epidermal proteolysis associated with increased kallikrein-related peptidases (KLKs) expression is also observed in both NS and psoriatic epidermis. Furthermore, reduced expression of desmosomal proteins is observed in NS, but increased in psoriasis. Since desmosomal proteins are proteolytic substrates and control keratinocyte differentiation, their altered expression directly links epidermal proteolysis to differentiation. In conclusion, abnormal cellular differentiation and proteolysis are interconnected and underlie the pathology of NS, SD and psoriasis.