Flower directs apically polarized trafficking of lamellar bodies to establish the epidermal barrier

Summary: Abstract Body: Apically polarized secretion of lamellar bodies (LBs) by stratum granulosum keratinocytes facilitates delivery of various lipids, structural proteins and enzymes to the stratum corneum for finalization of the epidermal barrier. While LB function is perturbed in numerous disorders of cornification, the molecular mechanisms regulating their formation and secretion are poorly understood. Here, we demonstrate that the Flower isoform, hFWE4, a putative Ca2+ channel with no previously described function in the epidermis is critical for biogenesis and Ca2+-dependent polarized transport of these unique organelles. Using Airyscan microscopy, proteomics approaches and epidermal organoid cultures, we find that hFWE4-positive LBs are abundant in human epidermis, originate from the Golgi apparatus and associate with a distinct ensemble of trafficking mediators shared across tissue specific lysosome related organelles. In a process required for maturation of the epidermal barrier, we find that incorporation of hFWE4 into LBs raises cytosolic Ca2+ to facilitate the cell surface targeting of these vesicles. Finally, supporting a critical role for hFWE4-dependent trafficking in establishing the epidermal barrier, we demonstrate that this process is dysregulated in Grover’s and Darier disease, cornifying disorders that are driven by impairments in keratinocyte Ca2+ handling. Our results establish hFWE4 as an important determinant of epidermal barrier function and a novel regulator of LB biogenesis and trafficking. Justin Rudd¹, Jos Smits², Patrick Kuwong¹, Rachel E. Johnson¹, Louise Monga¹, Ivonne van Vlijmen-Willems², Greer Porter¹, Kanika Sharma³, Vikas Kumar³, Mrinal Sarkar⁵, Ellen van den Bogaard², James Grunkemeyer¹, Johann E. Gudjonsson⁴, Sunny Wong⁵, Cory Simpson⁶, Laura Hansen¹ 1. Creighton University School of Medicine, Omaha, NE, United States. 2. Radboud Research Institute for Medical Innovation, Nijmegen, Netherlands. 3. University of Nebraska Medical Center, Omaha, NE, United States. 4. University of Michigan, Ann Arbor, MI, United States. 5. University of Michigan, Ann Arbor, MI, United States. 6. University of Washington, Seattle, WA, United States. Epidermal Structure and Barrier Function