Skin-Nerve Co-Culture Systems for Disease Modeling and Drug Discovery

Establishment of an in vitro cell coculture model for investigating the whitening mechanism of Paeonia lactiflora Pall seeds oil

BACKGROUND

In vitro single-cell experiments may yield inconsistent results compared to clinical trials. To enhance the reliability of cosmetic active ingredient screening, a coculture model of B16F10-HaCaT cells was established in vitro based on the structural characteristics of human skin, thereby improving the credibility of experimental outcomes. Currently, most cosmetic whitening additives primarily target simple efficacy goals such as inhibiting tyrosinase activity or melanin transfer. Therefore, investigating novel and efficient whitening additives has become a prominent research focus.

OBJECTIVES

The aim is to establish an in vitro cell coculture model for more reliable experimental results and investigate the mechanism by which Paeonia lactiflora Pall seeds oil inhibits melanin production and transfer.

METHODS

The impact of different concentrations of Paeonia lactiflora Pall seeds oil on cocultured cell proliferation rate was assessed using cck8 assay. Tyrosinase inhibition ability in cocultured cells was tested using levodopa as a substrate. Melanin production inhibition ability in coculture cells was evaluated by lysing cells with sodium hydroxide. The effect of Paeonia lactiflora Pall seeds oil on dendrite-related gene expression levels was examined through qPCR analysis. Additionally, Western blotting was employed to study the effect of Paeonia lactiflora Pall seeds oil on dendrite-related protein expression levels.

RESULTS

Different concentrations of Paeonia lactiflora Pall seeds oil did not affect the proliferation activity of cocultured cells. A specific concentration of α-MSH increased cell tyrosinase activity, cellular melanin content, as well as Rac1, Cdc42, and PAR-2 gene and protein expression related to dendritic formation. Treatment with a certain concentration of Paeonia lactiflora Pall seeds oil resulted in decreased tyrosinase activity and melanin content in cells along with downregulated expression levels of Rac1, Cdc42, and PAR-2 genes and proteins associated with dendritic formation.

CONCLUSIONS

Paeonia lactiflora Pall seeds oil at specific concentrations exhibits the ability to inhibit tyrosinase activity, decrease melanin content, and possesses the potential to impede melanin transfer.

Cutaneous-immuno-neuro-endocrine (CINE) system: A complex enterprise transforming skin into a super organ

Skin is now emerging as a complex realm of three chief systems viz. immune system, nervous system, and endocrine system. The cells involved in their intricate crosstalk, namely native skin cells, intra-cutaneous immune cells and cutaneous sensory neurons have diverse origin and distinct functions. However, recent studies have explored their role beyond their pre-defined functional boundaries, such that the cells shun their traditional functions and adopt unconventional roles. For example, the native skin cells, apart from providing for basic structural framework of skin, also perform special immune functions and participate in extensive neuro-endocrine circuitry, which were traditionally designated as functions of cutaneous resident immune cells and sensory neurons respectively. At the cellular level, this unique collaboration is brought out by special molecules called neuromediators including neurotransmitters, neuropeptides, neurotrophins, neurohormones and cytokines/chemokines. While this intricate crosstalk is essential for maintaining cutaneous homeostasis, its disruption is seen in various cutaneous diseases. Recent study models have led to a paradigm shift in our understanding of pathophysiology of many such disorders. In this review, we have described in detail the interaction of immune cells with neurons and native skin cells, role of neuromediators, the endocrine aspect in skin and current understanding of cutaneous neuro-immuno-endocrine loop in one of the commonest skin diseases, psoriasis. An accurate knowledge of this unique crosstalk can prove crucial in understanding the pathophysiology of different skin diseases and allow for generation of targeted therapeutic modalities.

The frontline of alternatives to animal testing: novel in vitro skin model application in drug development and evaluation

The FDA Modernization Act 2.0 has brought nonclinical drug evaluation into a new era. In vitro models are widely used and play an important role in modern drug development and evaluation, including early candidate drug screening and preclinical drug efficacy and toxicity assessment. Driven by regulatory steering and facilitated by well-defined physiology, novel in vitro skin models are emerging rapidly, becoming the most advanced area in alternative testing research. The revolutionary technologies bring us many in vitro skin models, either laboratory-developed or commercially available, which were all built to emulate the structure of the natural skin to recapitulate the skin's physiological function and particular skin pathology. During the model development, how to achieve balance among complexity, accessibility, capability, and cost-effectiveness remains the core challenge for researchers. This review attempts to introduce the existing in vitro skin models, align them on different dimensions, such as structural complexity, functional maturity, and screening throughput, and provide an update on their current application in various scenarios within the scope of chemical testing and drug development, including testing in genotoxicity, phototoxicity, skin sensitization, corrosion/irritation. Overall, the review will summarize a general strategy for in vitro skin model to enhance future model invention, application, and translation in drug development and evaluation.

New human in vitro co-culture model of keratinocytes and sensory neurons like cells releasing substance P with an evaluation of the expression of ZIKV entry receptors: A potent opportunity to test Zika virus entry and to study Zika virus' infection in neurons?

During the course of acute ZIKV infection, pruritus is a cardinal symptom widely documented in the literature. Its frequent association with dysesthesia and several dysautonomic manifestations, suggests a pathophysiological mechanism involving the peripheral nervous system. The aim of this study was to develop a functional human model to potentially able to be infected by ZIKV: by demonstrating the functionality on a new human model of co-culture of keratinocyte and sensory neuron derived from induced pluripotent stem cells using a classical method of capsaicin induction and SP release, and verify the presence of ZIKV entry receptor in these cells. Depending of cellular type, receptors of the TAMs family, TIMs (TIM1, TIM3 and TIM4) and DC-SIGN and RIG1 were present/detected. The cells incubations with capsaicin resulted in an increase of the substance P. Hence, this study demonstrated the possibility to obtain co-cultures of human keratinocytes and human sensory neurons that release substance P in the same way than previously published in animal models which can be used as a model of neurogenic skin inflammation. The demonstration of the expression of ZIKV entry receptors in these cells allows to considerate the potent possibility that ZIKV is able to infect cells.

Toward the Next Generation of Neural Iontronic Interfaces

Neural interfaces are evolving at a rapid pace owing to advances in material science and fabrication, reduced cost of scalable complementary metal oxide semiconductor (CMOS) technologies, and highly interdisciplinary teams of researchers and engineers that span a large range from basic to applied and clinical sciences. This study outlines currently established technologies, defined as instruments and biological study systems that are routinely used in neuroscientific research. After identifying the shortcomings of current technologies, such as a lack of biocompatibility, topological optimization, low bandwidth, and lack of transparency, it maps out promising directions along which progress should be made to achieve the next generation of symbiotic and intelligent neural interfaces. Lastly, it proposes novel applications that can be achieved by these developments, ranging from the understanding and reproduction of synaptic learning to live-long multimodal measurements to monitor and treat various neuronal disorders.

Self-Assembled Fibrinogen Scaffolds Support Cocultivation of Human Dermal Fibroblasts and HaCaT Keratinocytes

Self-assembled fibrinogen scaffolds are highly attractive biomaterials to mimic native blood clots. To explore their potential for wound healing, we studied the interaction of cocultures of human dermal fibroblasts (HDFs) and HaCaT keratinocytes with nanofibrous, planar, and physisorbed fibrinogen. Cell viability analysis indicated that the growth of HDFs and HaCaTs was supported by all fibrinogen topographies until 14 days, either in mono- or coculture. Using scanning electron microscopy and cytoskeletal staining, we observed that the native morphology of both cell types was preserved on all topographies. Expression of the marker proteins vimentin and cytokeratin-14 showed that the native phenotype of fibroblasts and undifferentiated keratinocytes, respectively, was maintained. HDFs displayed their characteristic wound healing phenotype, characterized by expression of fibronectin. Finally, to mimic the multilayered microenvironment of skin, we established successive cocultures of both cells, for which we found consistently high metabolic activities. SEM analysis revealed that HaCaTs arranged into a confluent top layer after 14 days, while fluorescent labeling confirmed the presence of both cells in the layered structure after 6 days. In conclusion, all fibrinogen topographies successfully supported the cocultivation of fibroblasts and keratinocytes, with fibrinogen nanofibers being particularly attractive for skin regeneration due to their biomimetic porous architecture and the technical possibility to be detached from an underlying substrate.

Recent advances for using human induced-pluripotent stem cells as pain-in-a-dish models of neuropathic pain

Neuropathic pain is amongst the most common non-communicable disorders and the poor effectiveness of current treatment is an unmet need. Although pain is a universal experience, there are significant inter-individual phenotypic differences. Developing models that can accurately recapitulate the clinical pain features is crucial to better understand underlying pathophysiological mechanisms and find innovative treatments. Current data from heterologous expression systems that investigate properties of specific molecules involved in pain signaling, and from animal models, show limited success with their translation into the development of novel treatments for pain. This is in part because they do not recapitulate the native environment in which a particular molecule functions, and due to species-specific differences in the properties of several key molecules that are involved in pain signaling. The limited availability of post-mortem tissue, in particular dorsal root ganglia (DRG), has hampered research using human cells in pre-clinical studies. Human induced-pluripotent stem cells (iPSCs) have emerged as an exciting alternative platform to study patient-specific diseases. Sensory neurons that are derived from iPSCs (iPSC-SNs) have provided new avenues towards elucidating peripheral pathophysiological mechanisms, the potential for development of personalized treatments, and as a cell-based system for high-throughput screening for discovering novel analgesics. Nevertheless, reprogramming and differentiation protocols to obtain nociceptors have mostly yielded immature homogenous cell populations that do not recapitulate the heterogeneity of native sensory neurons. To close the gap between native human tissue and iPSCs, alternative strategies have been developed. We will review here recent developments in differentiating iPSC-SNs and their use in pre-clinical translational studies. Direct conversion of stem cells into the cells of interest has provided a more cost- and time-saving method to improve reproducibility and diversity of sensory cell types. Furthermore, multi-cellular strategies that mimic in vivo microenvironments for cell maturation, by improving cell contact and communication (co-cultures), reproducing the organ complexity and architecture (three-dimensional organoid), and providing iPSCs with the full spatiotemporal context and nutrients needed for acquiring a mature phenotype (xenotransplantation), have led to functional sensory neuron-like systems. Finally, this review touches on novel prospective strategies, including fluorescent-tracking to select the differentiated neurons of relevance, and dynamic clamp, an electrophysiological method that allows direct manipulation of ionic conductances that are missing in iPSC-SNs.

Cellular Pathogenesis of Chemotherapy-Induced Peripheral Neuropathy: Insights From Drosophila and Human-Engineered Skin Models

Chemotherapy-induced peripheral neuropathy (CIPN) is a highly prevalent and complex condition arising from chemotherapy cancer treatments. Currently, there are no treatment or prevention options in the clinic. CIPN accompanies pain-related sensory functions starting from the hands and feet. Studies focusing on neurons in vitro and in vivo models significantly advanced our understanding of CIPN pathological mechanisms. However, given the direct toxicity shown in both neurons and non-neuronal cells, effective in vivo or in vitro models that allow the investigation of neurons in their local environment are required. No single model can provide a complete solution for the required investigation, therefore, utilizing a multi-model approach would allow complementary advantages of different models and robustly validate findings before further translation. This review aims first to summarize approaches and insights from CIPN in vivo models utilizing small model organisms. We will focus on Drosophila melanogaster CIPN models that are genetically amenable and accessible to study neuronal interactions with the local environment in vivo. Second, we will discuss how these findings could be tested in physiologically relevant vertebrate models. We will focus on in vitro approaches using human cells and summarize the current understanding of engineering approaches that may allow the investigation of pathological changes in neurons and the skin environment.

In Vitro Sensitive Skin Models: Review of the Standard Methods and Introduction to a New Disruptive Technology

The skin is a protective organ, able to decode a wide range of tactile, thermal, or noxious stimuli. Some of the sensors belonging to the transient receptor potential (TRP) family, for example, TRPV1, can elicit capsaicin-induced heat pain or histamine-induced itching sensations. The sensory nerve fibers, whose soma is located in the trigeminal or the dorsal root ganglia, are able to carry signals from the skin’s sensory receptors toward the brain via the spinal cord. In some cases, in response to environmental factors, nerve endings might be hyper activated, leading to a sensitive skin syndrome (SSS). SSS affects about 50% of the population and is correlated with small-fiber neuropathies resulting in neuropathic pain. Thus, for cosmetical and pharmaceutical industries developing SSS treatments, the selection of relevant and predictive in vitro models is essential. In this article, we reviewed the different in vitro models developed for the assessment of skin and neuron interactions. In a second part, we presented the advantages of microfluidic devices and organ-on-chip models, with a focus on the first model we developed in this context.

Fibroblasts as an experimental model system for the study of comparative physiology

Mechanistic evaluations of processes that underlie organism-level physiology often require reductionist approaches. Dermal fibroblasts offer one such approach. These cells are easily obtained from minimally invasive skin biopsy, making them appropriate for the study of protected and/or logistically challenging species. Cell culture approaches permit extensive and fine-scale sampling regimes as well as gene manipulation techniques that are not feasible in vivo. Fibroblast isolation and culture protocols are outlined here for primary cells, and the benefits and drawbacks of immortalization are discussed. We show examples of physiological metrics that can be used to characterize primary cells (oxygen consumption, translation, proliferation) and readouts that can be informative in understanding cell-level responses to environmental stress (lactate production, heat shock protein induction). Importantly, fibroblasts may display fidelity to whole animal physiological phenotypes, facilitating their study. Fibroblasts from Antarctic Weddell seals show greater resilience to low temperatures and hypoxia exposure than fibroblasts from humans or rats. Fibroblast oxygen consumption rates are not affected by temperature stress in the heat-tolerant camel, whereas similar temperature exposures depress mitochondrial metabolism in fibroblasts from rhinoceros. Finally, dermal fibroblasts from a hibernator, the meadow jumping mouse, better resist experimental cooling than a fibroblast line from the laboratory mouse, with the hibernator demonstrating a greater maintenance of homeostatic processes such as protein translation. These results exemplify the parallels that can be drawn between fibroblast physiology and expectations in vivo, and provide evidence for the power of fibroblasts as a model system to understand comparative physiology and biomedicine.