Shining a Light on Black Holes in Keratinocytes

Laser-induced vapor nanobubbles for B16-F10 melanoma cell killing and intracellular delivery of chemotherapeutics

The most lethal form of skin cancer is cutaneous melanoma, a tumor that develops in the melanocytes, which are found in the epidermis. The treatment strategy of melanoma is dependent on the stage of the disease and often requires combined local and systemic treatment. Over the years, systemic treatment of melanoma has been revolutionized and shifted toward immunotherapeutic approaches. Phototherapies like photothermal therapy (PTT) have gained considerable attention in the field, mainly because of their straightforward applicability in melanoma skin cancer, combined with the fact that these strategies are able to induce immunogenic cell death (ICD), linked with a specific antitumor immune response. However, PTT comes with the risk of uncontrolled heating of the surrounding healthy tissue due to heat dissipation. Here, we used pulsed laser irradiation of endogenous melanin-containing melanosomes to induce cell killing of B16-F10 murine melanoma cells in a non-thermal manner. Pulsed laser irradiation of the B16-F10 cells resulted in the formation of water vapor nanobubbles (VNBs) around endogenous melanin-containing melanosomes, causing mechanical cell damage. We demonstrated that laser-induced VNBs are able to kill B16-F10 cells with high spatial resolution. When looking more deeply into the cell death mechanism, we found that a large part of the B16-F10 cells succumbed rapidly after pulsed laser irradiation, reaching maximum cell death already after 4 h. Practically all necrotic cells demonstrated exposure of phosphatidylserine on the plasma membrane and caspase-3/7 activity, indicative of regulated cell death. Furthermore, calreticulin, adenosine triphosphate (ATP) and high-mobility group box 1 (HMGB1), three key damage-associated molecular patterns (DAMPs) in ICD, were found to be exposed from B16-F10 cells upon pulsed laser irradiation to an extent that exceeded or was comparable to the bona fide ICD-inducer, doxorubicin. Finally, we could demonstrate that VNB formation from melanosomes induced plasma membrane permeabilization. This allowed for enhanced intracellular delivery of bleomycin, an ICD-inducing chemotherapeutic, which further boosted cell death with the potential to improve the systemic antitumor immune response.

Tranexamic acid may promote melanocores clustering in keratinocytes through upregulation of Rab5b

Tranexamic acid (TXA) is a promising therapeutic agent in melasma that can act on multiple pathophysiologic mechanisms of melasma. However, it is unclear whether TXA affects melanin in keratinocytes. To explore the effect of TXA on melanocores in keratinocytes. The melanocore-incorporated keratinocytes were constructed by co-incubating normal human epidermal keratinocytes (NHEK) with melanocores. After being treated with TXA, autophagy- and melanin-related protein expressions were detected. Then, transcriptome sequencing was used to compare the genetic changes in melanocore-incorporated keratinocytes before and after TXA treatment and further verified the differentially expressed genes. At the same time, the distribution of melanocores in human keratinocytes was observed by transmission electron microscopy. We found that TXA does not promote melanin degradation in primary keratinocytes by inducing autophagy. Protein transport and intracellular protein transport-related genes were enriched after TXA treatment, and Rab5b was significantly upregulated. Transmission electron microscopy showed that the percentage of melanocores distributed in clusters increased after treatment with TXA, which was reduced after Rab5b silencing. In addition, results suggested that melanocores could colocalize with Rab5b and lysosome-associated membrane protein1 (LAMP1). Our study found that Rab5b may be involved in the melanocore distribution in keratinocytes. TXA may promote the clustering distribution of endocytic melanocores through upregulation of Rab5b, representing a potential mechanism of TXA treatment against melasma.

Primary Ciliary Signaling in the Skin-Contribution to Wound Healing and Scarring

Primary cilia (PC) are solitary, post-mitotic, microtubule-based, and membrane-covered protrusions that are found on almost every mammalian cell. PC are specialized cellular sensory organelles that transmit environmental information to the cell. Signaling through PC is involved in the regulation of a variety of cellular processes, including proliferation, differentiation, and migration. Conversely, defective, or abnormal PC signaling can contribute to the development of various pathological conditions. Our knowledge of the role of PC in organ development and function is largely based on ciliopathies, a family of genetic disorders with mutations affecting the structure and function of PC. In this review, we focus on the role of PC in their major signaling pathways active in skin cells, and their contribution to wound healing and scarring. To provide comprehensive insights into the current understanding of PC functions, we have collected data available in the literature, including evidence across cell types, tissues, and animal species. We conclude that PC are underappreciated subcellular organelles that significantly contribute to both physiological and pathological processes of the skin development and wound healing. Thus, PC assembly and disassembly and PC signaling may serve as attractive targets for antifibrotic and antiscarring therapies.