Function of Desmoglein 1/Pemphigus Foliaceus Antigen

The multi-layered epidermis provides an essential barrier against water loss, physical insults, and infection. Its proper function requires that architectural features be polarized along its entire apical to basal axis. Contributing to the inherent tissue polarity of the epidermis are seven desmosomal cadherins, intercellular adhesion molecules that provide mechanical integrity to tissues by anchoring intermediate filaments to the plasma membrane. Of these, desmoglein 1 (Dsg1) appeared late in evolution along with expansion of epidermal functions to meet the challenges of life on land. We showed that Dsg1, which is first expressed as cells commit to differentiate and transit into the suprabasal layers, acts as a scaffold that engages the actin cytoskeleton and signaling mediators necessary for tissue morphogenesis and terminal differentiation. To achieve these functions Dsg1 must be properly routed by intracellular trafficking machinery to its final address at the plasma membrane. Its failure to accumulate on the plasma membrane disrupts organismal homeostasis in patients with the systemic inflammatory disorder, Severe dermatitis, Allergies and Metabolic wasting (SAM) syndrome, a syndrome we helped identify. We identified two critical elements of the trafficking machinery required for Dsg1 function-- a specific dynein microtubule motor complex and an endosomal sorting complex called the retromer, best known to be involved in neurodegenerative disorders. We hypothesize that in keratinocytes committing to differentiate, the retromer/dynein machinery ensures Dsg1 gets to the right plasma membrane “address” and in the right amount, to mediate a switch from EGFR signaling to actin remodeling that drives changes in cell mechanics and signaling necessary for morphogenesis and immune regulation. We will use optical imaging, biochemistry, and genetic interference in human 2D and 3D organotypic cultures, human patient materials, and knockout mouse models to: 1) Define how the retromer and dynein trafficking machinery ensures Dsg1’s functional placement on the plasma membrane necessary to promote the epithelial basal to suprabasal transition, and evaluate the utility of retromer chaperones as a therapeutic strategy to enhance epidermal stratification and differentiation in vitro and in vivo; 2) Determine how Dsg1 coordinates a switch from EGFR signaling to actin remodeling by engaging the actin nucleation promoting factors N-WASP and Arp2/3 to drive cell mechanics necessary for stratification in vitro and in vivo; and 3) Address the extent to which Dsg1 governs redistribution of actin remodeling factors to control epidermal immune regulation and expression of IL-23, a pro-inflammatory cytokine that increases in SAM syndrome caused by loss of Dsg1 function. These studies will establish how Dsg1 coordinates rearrangements of the cytoskeleton with the biochemical program of differentiation while keeping inflammatory cytokines in check. Understanding how Dsg1 dynamics and downstream signaling are impacted in skin disorders will be essential for developing new ways to repair and strengthen physical and immune barriers of epithelia.

The multi-layered epidermis provides an essential barrier against water loss, physical insults, and infection. Its proper function requires that architectural features be polarized along its entire apical to basal axis. Contributing to the inherent tissue polarity of the epidermis are seven desmosomal cadherins, intercellular adhesion molecules that provide mechanical integrity to tissues by anchoring intermediate filaments to the plasma membrane. Of these, desmoglein 1 (Dsg1) appeared late in evolution along with expansion of epidermal functions to meet the challenges of life on land. We showed that Dsg1, which is first expressed as cells commit to differentiate and transit into the suprabasal layers, acts as a scaffold that engages the actin cytoskeleton and signaling mediators necessary for tissue morphogenesis and terminal differentiation. To achieve these functions Dsg1 must be properly routed by intracellular trafficking machinery to its final address at the plasma membrane. Its failure to accumulate on the plasma membrane disrupts organismal homeostasis in patients with the systemic inflammatory disorder, Severe dermatitis, Allergies and Metabolic wasting (SAM) syndrome, a syndrome we helped identify. We identified two critical elements of the trafficking machinery required for Dsg1 function-- a specific dynein microtubule motor complex and an endosomal sorting complex called the retromer, best known to be involved in neurodegenerative disorders. We hypothesize that in keratinocytes committing to differentiate, the retromer/dynein machinery ensures Dsg1 gets to the right plasma membrane “address” and in the right amount, to mediate a switch from EGFR signaling to actin remodeling that drives changes in cell mechanics and signaling necessary for morphogenesis and immune regulation. We will use optical imaging, biochemistry, and genetic interference in human 2D and 3D organotypic cultures, human patient materials, and knockout mouse models to: 1) Define how the retromer and dynein trafficking machinery ensures Dsg1’s functional placement on the plasma membrane necessary to promote the epithelial basal to suprabasal transition, and evaluate the utility of retromer chaperones as a therapeutic strategy to enhance epidermal stratification and differentiation in vitro and in vivo; 2) Determine how Dsg1 coordinates a switch from EGFR signaling to actin remodeling by engaging the actin nucleation promoting factors N-WASP and Arp2/3 to drive cell mechanics necessary for stratification in vitro and in vivo; and 3) Address the extent to which Dsg1 governs redistribution of actin remodeling factors to control epidermal immune regulation and expression of IL-23, a pro-inflammatory cytokine that increases in SAM syndrome caused by loss of Dsg1 function. These studies will establish how Dsg1 coordinates rearrangements of the cytoskeleton with the biochemical program of differentiation while keeping inflammatory cytokines in check. Understanding how Dsg1 dynamics and downstream signaling are impacted in skin disorders will be essential for developing new ways to repair and strengthen physical and immune barriers of epithelia.