Keratinocyte-derived TGFβ is not required to maintain skin immune homeostasis

Targeted deletion of TGFβ1 in basal keratinocytes causes profound defects in stratified squamous epithelia and aberrant melanocyte migration

Transforming Growth Factor Beta 1 (TGFβ1) is a multifunctional cytokine that regulates proliferation, apoptosis, and epithelial-mesenchymal transition of epithelial cells. While its role in cancer is well studied, less is known about TGFβ1 and regulation of epithelial development. To address this, we deleted TGFβ1 in basal keratinocytes of stratified squamous epithelia. Newborn mice with a homozygous TGFβ1 deletion had significant defects in proliferation and differentiation of the epidermis and oral mucosa, and died shortly after birth. Hair follicles were sparse in TGFβ1 depleted skin and had delayed development. Additionally, the Wnt pathway transcription factor LEF1 was reduced in hair follicle bulbs and nearly absent from the basal epithelial layer. Hemizygous knockout mice survived to adulthood but were runted and had sparse coats. The skin of these mice had irregular hair follicle morphology and aberrant hair cycle progression, as well as abnormally high melanin expression and delayed melanocyte migration. In contrast to newborn TGFβ1 null mice, the epidermis was hyperproliferative, acanthotic and inflamed. Expression of p63, a master regulator of stratified epithelial identity, proliferation and differentiation, was reduced in TGFβ1 null newborn epidermis but expanded in the postnatal acanthotic epidermis of TGFβ1 hemizygous mice. Thus, TGFβ1 is both essential and haploinsufficient with context dependent roles in stratified squamous epithelial development and homeostasis.

Transcriptomic Profiling Revealed Plexin A2 Downregulation With Migration and Invasion Alteration in Dacarbazine-Treated Primary Melanoma Cells

Melanoma is highly heterogeneous type of malignant neoplasm that is responsible for the majority of deaths among other types of skin cancer. In the present study, we screened a list of differentially expressed genes in two primary, drug-naïve melanoma cell lines derived from patients with melanoma following treatment of the cells with the chemotherapeutic agent dacarbazine. The aim was to determine the transcriptomic profiles and associated alterations in the cell phenotype. We found the vascular endothelial growth factor A/vascular endothelial growth factor receptor 2, phosphoinositide 3-kinase/protein kinase B and focal adhesion signaling pathways to be top altered after dacarbazine treatment. In addition, we observed the expression levels of genes associated with tumor dissemination, integrin β8 and matrix metalloproteinase-1, to be diminished in both cell lines studied, the results of which were confirmed by reverse transcription-quantitative polymerase chain reaction. By contrast, plexin A2 expression was found to be upregulated in K2303 cells, where reduced migration and invasion were also observed, following dacarbazine treatment. Plexin A2 downregulation was associated with the promotion of migrative and invasive capacities in B0404 melanoma cells. Since plexin A2 is semaphorin co-receptor that is involved in focal adhesion and cell migration regulation, the present study suggested that plexin A2 may be implicated in the dacarbazine-mediated phenotypic shift of melanoma cells. We propose that the signature of cancer cell invasiveness can be revealed by using a combination of transcriptomic and functional approaches, which should be applied in the development of personalized therapeutic strategies for each patient with melanoma.

Keratinocytes Regulate the Threshold of Inflammation by Inhibiting T Cell Effector Functions

Whilst the importance of keratinocytes as a first-line defense has been widely investigated, little is known about their interactions with non-resident immune cells. In this study, the impact of human keratinocytes on T cell effector functions was analyzed in an antigen-specific in vitro model of allergic contact dermatitis (ACD) to nickel sulfate. Keratinocytes partially inhibited T cell proliferation and cytokine production. This effect was dependent on the keratinocyte/T cell ratio and was partially reversible by increasing the number of autologous dendritic cells. The inhibition of T cell proliferation by keratinocytes was independent of the T cell subtype and antigen presentation by different professional antigen-presenting cells. Autologous and heterologous keratinocytes showed comparable effects, while the fixation of keratinocytes with paraformaldehyde abrogated the immunosuppressive effect. The separation of keratinocytes and T cells by a transwell chamber, as well as a cell-free keratinocyte supernatant, inhibited T cell effector functions to the same amount as directly co-cultured keratinocytes, thus proving that soluble factor/s account for the observed suppressive effects. In conclusion, keratinocytes critically control the threshold of inflammatory processes in the skin by inhibiting T cell proliferation and cytokine production.

TGF-β: Many Paths to CD103+ CD8 T Cell Residency

CD8 tissue-resident memory T (T_RM) cells primarily reside in nonlymphoid tissues without recirculating and provide front-line protective immunity against infections and cancers. CD8 T_RM cells can be generally divided into CD69⁺ CD103⁻ T_RM cells (referred to as CD103⁻ T_RM cells) and CD69⁺ CD103⁺ T_RM cells (referred to as CD103⁺ T_RM cells). TGF-β plays a critical role in the development and maintenance of CD103⁺ CD8 T_RM cells. In this review, we summarize the current understanding of tissue-specific activation of TGF-β mediated by integrins and how it contributes to CD103⁺ CD8 T_RM cell development and maintenance. Furthermore, we discuss the underlying mechanisms utilized by TGF-β to regulate the development and maintenance of CD103⁺ CD8 T_RM cells. Overall, this review highlights the importance of TGF-β in regulating this unique subset of memory CD8 T cells that may shed light on improving vaccine design to target this population.

Competition for Active TGFβ Cytokine Allows for Selective Retention of Antigen-Specific Tissue- Resident Memory T Cells in the Epidermal Niche

Following antigen-driven expansion in lymph node, transforming growth factor-β (TGFβ) is required for differentiation of skin-recruited CD8⁺ T cell effectors into epidermal resident memory T (Trm) cells and their epidermal persistence. We found that the source of TGFβ -supporting Trm cells was autocrine. In addition, antigen-specific Trm cells that encountered cognate antigen in the skin, and bystander Trm cells that did not, both displayed long-term persistence in the epidermis under steady-state conditions. However, when the active-TGFβ was limited or when new T cell clones were recruited into the epidermis, antigen-specific Trm cells were more efficiently retained than bystander Trm cells. Genetically enforced TGFβR signaling allowed bystander Trm cells to persist in the epidermis as efficiently as antigen-specific Trm cells in both contexts. Thus, competition between T cells for active TGFβ represents an unappreciated selective pressure that promotes the accumulation and persistence of antigen-specific Trm cells in the epidermal niche.

Regulation of barrier immunity and homeostasis by integrin-mediated transforming growth factor β activation

Transforming growth factor β (TGF‐β) is a multifunctional cytokine that regulates cell growth, differentiation, adhesion, migration and death dependent on cell type, developmental stage, or tissue conditions. Various cell types secrete TGF‐β, but always as an inactive complex. Hence, for TGF‐β to function, this latent complex must somehow be activated. Work in recent years has highlighted a critical role for members of the α_v integrin family, including α_vβ₁, α_vβ₃, α_vβ₅, α_vβ₆ and α_vβ₈ that are involved in TGF‐β activation in various contexts, particularly at barrier sites such as the gut, lung and skin. The integrins facilitating this context‐ and location‐specific regulation can be dysregulated in certain diseases, so are potential therapeutic targets in a number of disorders. In this review, we discuss the role of TGF‐β at these barrier sites with a focus on how integrin‐mediated TGF‐β activation regulates tissue and immune homeostasis, and how this is altered in disease.