Lu Q. Le

Oil-producing sebaceous glands (SGs), attached to the upper/middle portion of hair follicles, are indispensable for maintaining skin hydration, and their dysfunction leads to dry skin. However, the molecular mechanisms underlying regulation of SG stem cells remain largely unknown. We identified transcription factor KROX20 as a marker of SG stem cells that sustains their stemness throughout SG morphogenesis and homeostasis. We developed an inducible mouse model in which ablation of KROX20-positive cells causes SG loss and rapidly and robustly induces dry, flaky, alopecia symptoms following induction. This model, termed xeroflacia (xero = xerosis, fla = flaky, cia = alopecia), provides a tool for studying the biology of dry skin. Furthermore, we found that KROX20 directly regulates Notch1 transcription to orchestrate the balance between SG stem cell self-renewal and differentiation. Small molecule drug modulation of Notch1 signaling to activate or inhibit the pathway enabled us to regulate SG differentiation to maintain skin oil levels, providing a proof of principle that other signaling pathways downstream of Krox20 could be therapeutic targets for SG-related diseases.

Meibomian gland dysfunction (MGD) is the leading cause of Dry Eye Disease (DED), accounting for approximately 90% of DED cases worldwide. The transcription factor KROX20 has been shown to mark stem cells that play a critical role in Meibomian gland (MG) development and homeostasis, however, the molecular mechanisms underlying these processes are not well understood. In this report, we used multiple Krox20 lineage tracing and ablation studies to investigate lineage commitment during MG morphogenesis and homeostasis. KROX20 marks MG stem cell pools, and regulates cellular contributions to the glands, as loss of Krox20 leads to MG atrophy, while its overexpression results in MG enlargement. We also found that Notch1 signaling is regulated by KROX20 and that ablation of the Notch1 gene in KROX20-expressing cells leads to MG atrophy, while Notch1 overexpression partially rescues MG atrophy caused by the loss of Krox20. Together, these results reveal a critical Krox20-Notch1 regulatory pathway in MG stem cells. Activation of Notch1 signaling may offer a novel approach to preventing or treating DED caused by depletion of the MG stem cell pool that can occur with ageing.

Mammalian skin is a vital barrier with the epidermis serving as its protective outer layer, continually undergoing renewal. Given that loss of the epidermis or its barrier function is lethal for mammals, multiple stem cell populations likely exist for the interfollicular epidermis (IFE), enhancing evolutionary survival. Here, we demonstrate that transcription factor KROX20 marks a heterogeneous stem cell population in the upper and middle mouse hair follicle (HF), partially overlapping with known HF stem cell markers in those regions. Lineage tracing in mice using different reporter lines shows that Krox20 -lineage cells migrate from the HF to the IFE, contributing to both basal and suprabasal layers during adulthood. Spatial transcriptomics data corroborate our findings. Depletion of epithelial Krox20 -expressing cells leads to epidermal hyperplasia and a disruption of stratification during homeostasis. Our study highlights the contribution of hair follicle Krox20 -lineage cells to the IFE and the regulation of epidermal homeostasis.

Plexiform neurofibromas (PNFs) are benign tumors of the peripheral nervous system that represent a major source of morbidity in neurofibromatosis type 1 (NF1). A substantial proportion of patients do not respond to current therapies or experience intolerable side effects. Transcriptomic characterization of murine and human PNF at bulk and single-cell resolution identified transforming growth factor–β (TGFβ) signaling as a key upstream regulator, driving aberrant basement membrane (BM) protein production by neoplastic Schwann cells and Fbs. Conditional TGFβ1 overexpression in Nf1 -deficient Schwann cells driven by Hoxb7- Cre promoted PNF growth and malignant transformation in vivo. Conversely, pharmacologic inhibition of the type I TGFβ receptor (TGFβRI) reduced PNF tumor burden in Nf1 mutant mice. Proteomic characterization of the extracellular matrix (ECM) showed reduced BM proteins upon TGFβRI inhibition. These findings implicate TGFβ as a potential therapeutic target in PNF and provide insights into the role of TGFβ signaling in orchestrating ECM dynamics in the PNF microenvironment.