Programmed cell death of keratinocytes culminates in apoptotic secretion of a humectant upon secretagogue action of acetylcholine

Vu Thuong Nguyen, Assane Ndoye, Leon L. Hall, Shaheen Zia, Juan Arredondo, Alexander I. Chernyavsky, David A. Kist, Brian D. Zelickson, Monica A. Lawry, Sergei A. Grando

Research output: Contribution to journalArticlepeer-review

50 Scopus citations

Abstract

The programmed cell death of the stratified squamous epithelial cells comprising human epidermis culminates in abrupt transition of viable granular keratinocytes (KC) into dead corneocytes sloughed by the skin. The granular cell-corneocyte transition is associated with a loss in volume and dry cell weight but the mechanism for and biological significance of this form of keratinocyte apoptosis remain obscure. We show that terminally differentiated KC extrude into the intercellular spaces of living epidermis the cytoplasmic buds containing randomly congregated components of the cytosol as well as filaggrin, a precursor of the natural moisturizing factor. The discharge of secretory product is reminiscent of holocrine secretion, suggesting the term 'apoptotic secretion' for this novel, essential step in the process of cornification. The secretory product may become a part of the glycocalyx (a.k.a. 'intercellular cement substance' of epidermis) and serve as a humectant that counterbalances the osmotic pressure imposed by the natural moisturizing factor located in the stratum corneum comprised by corneocytes. The apoptotic secretion commences upon secretagouge action of acetylcholine which is synthesized and released by KC. A combination of a cholinergic nicotinic agonist and a muscarinic antagonist which increases intracellular calcium levels is required to trigger the apoptotic secretion. Analysis of the relative amounts of cholinergic enzymes and receptors expressed by KC capable of secretion and the pharmacological profiles of secretion regulation revealed an upward concentration gradient of free acetylcholine in epidermis which may provide for its unopposed secretagogue action via the m1 muscarinic and the α7, and α9 nicotinic receptor types expressed by KC at the latest stage of their development in the epidermis.

Original languageEnglish (US)
Pages (from-to)1189-1204
Number of pages16
JournalJournal of cell science
Volume114
Issue number6
StatePublished - Apr 23 2001

Keywords

  • Acetylcholine
  • Cornification
  • Filaggrin
  • Keratinocyte
  • Muscarinic receptor
  • Nicotinic receptor

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