Engrailed-1 in eccrine sweat gland development and regeneration: from evolutionary innovation to therapeutic perspectives

Functional regeneration of eccrine sweat glands (ESGs) remains a major unmet need in burns and trauma, where extensive skin loss leads to permanent anhidrosis, life-threatening hyperthermia, and impaired quality of life. Here we synthesize evidence pointing to the homeodomain transcription factor Engrailed-1 (EN1) as a central regulator that coordinates ESG development across four interconnected biological functions: (1) establishing a permissive ventral limb field by repressing the WNT7A–LMX1B dorsalization pathway; (2) executing a binary fate switch that suppresses the hair follicle program while activating a pro-glandular program; (3) functioning as a quantitative rheostat whose expression levels determine ESG density—a mechanism potentiated by primate-specific enhancers such as ECE18; and (4) being required for the establishment of a transient eccrine niche (EDEN) that provides mesenchymal support during gland morphogenesis in mouse models. Drawing on this framework, we propose a tiered pathogenesis–regeneration model (Tiers 1–4) mapping to distinct EN1 failures: Tier 1 (ventral field loss) points to bioengineered glabrous skin substitutes; Tier 2 (lineage specification failure) guides strategies to redirect progenitor fate; Tier 3 (aborted morphogenesis) highlights the need for EDEN-like niche reconstruction; and Tier 4 (compromised adult integrity) suggests approaches to reinforce the mechanical anchor of existing glands through EN1-mediated regulation of epidermal isoform of Bullous Pemphigoid Antigen 1 (BPAG1e), a proposed function inferred from in vitro evidence but untested in vivo . This multi-tiered model offers a conceptual framework for functional ESG restoration while addressing translational gaps between embryonic programs and adult tissue competency—a framework that remains speculative and requires rigorous validation in human tissues, as many mechanisms are supported primarily by mouse studies.