SPRR1A (small proline-rich protein 1A) is a keratinocyte differentiation marker and structural protein critical for epidermal barrier function. Primarily, SPRR1A functions as a cross-linked envelope protein in keratinocytes that becomes incorporated into the cornified envelope through transglutaminase-mediated cross-linking with membrane proteins 1. Its expression is regulated by AP-1 and Ets transcription factors during calcium-induced and TPA-induced keratinocyte terminal differentiation 1. Beyond its canonical role in skin, SPRR1A expression extends to respiratory epithelium, where it is expressed in squamous cells and intermediate alveolar epithelial cells 23. In disease contexts, dysregulated SPRR1A expression carries significant pathological implications. In cardiac fibroblasts, SPRR1A acts as a pro-fibrotic effector downstream of miR-150, with upregulation contributing to adverse remodeling post-myocardial infarction; miR-150-mediated SPRR1A repression is cardioprotective 4. In pancreatic ductal adenocarcinoma, elevated SPRR1A expression independently predicts poor prognosis and reduced survival, though mechanistic studies suggest it may be a consequence rather than driver of aggressive phenotypes 5. In pulmonary fibrosis, Sprr1a+ intermediate epithelial cells function as pathogenic drivers; their selective depletion markedly reduces fibrosis in bleomycin-injured mice 3. Conversely, SPRR1A downregulation is associated with poor outcomes in HPV16-negative head and neck squamous cell carcinoma 6. Recent evidence demonstrates SPRR1A as a druggable target in psoriasis, where its inhibition by compounds like calycosin restores epidermal barrier function and reduces inflammation 78.