Increased in vitro expression of beta2-adrenoceptors in differentiating lesional keratinocytes of vitiligo patients

Abstract

Keratinocytes were established in serum-free culture medium from lesional and nonlesional skin of a patient with vitiligo (skin type III) and from an age-matched healthy control subject. Both differentiating and undifferentiated cells were examined for the presence of beta 2-adrenoceptors in culture medium containing either low (0.1 x 10(-3) M) or high (1.5 x 10(-3) M) calcium concentrations. Binding experiments were performed with saturating levels of radiolabeled (--)-[3H] CGP 12177, a nonselective beta-adrenergic antagonist. Controls for nonspecific binding were determined by the addition of the beta-adrenergic antagonist, propranolol (5 mumol), before the introduction of (--)-[3H] CGP 12177 to cell cultures. Undifferentiated keratinocytes yielded the highest expression of beta 2-adrenoceptors, whereas differentiating keratinocytes grown in medium with a low calcium concentration (0.1 x 10(-3) M) had a significantly lower expression of receptors with the exception of vitiliginous cells, which retained high densities of receptors, similar to undifferentiated cells. In addition, these vitiliginous keratinocytes showed a defect in 45calcium uptake. In contrast, differentiated keratinocytes from all three cell strains, grown in medium containing a high calcium concentration (1.5 x 10(-3) M) revealed a significantly lower receptor density compared to undifferentiated cells. This finding identified the importance of the extracellular calcium concentration in the expression of beta 2-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta Adrenergic Receptors in Keratinocytes

“…This finding was confirmed by later studies that investigated binding affinities of selective agonists and antagonists [10][11][12], radioligand-binding assays of epidermal membrane fragments [3], and autoradiographic mapping of the beta adrenergic receptor subtypes on epidermal keratinocytes [4]. Since only the beta2AR is expressed in keratinocytes, this review will focus on this receptor subtype and its physiological role in the epidermis.…”

“…This defect, along with a concomitantly noted reduction in the activity of PNMT, in keratinocytes in affected vitiliginous epidermis [58] (Figure 2) may explain, in part, the accumulation of norepinephrine. Third, epidermal keratinocytes derived from the affected skin of patients with vitiligo (and not the clinically normal appearing skin in these patients), demonstrate increased expression of the beta2AR in culture [12]. The expression of these receptors on keratinocytes are regulated by extracellular levels of calcium [12] as well as by 6-biopterin, the redox product of 6BHR, which is increased in the epidermis in patients with vitiligo (reviewed in [13,61]).…”

“…Third, epidermal keratinocytes derived from the affected skin of patients with vitiligo (and not the clinically normal appearing skin in these patients), demonstrate increased expression of the beta2AR in culture [12]. The expression of these receptors on keratinocytes are regulated by extracellular levels of calcium [12] as well as by 6-biopterin, the redox product of 6BHR, which is increased in the epidermis in patients with vitiligo (reviewed in [13,61]). Since beta2AR activation by catecholamines also induces calcium influx into keratinocytes [14], one might have anticipated that intracellular calcium levels are increased in keratinocytes in vitiliginous epidermis.…”

“…The beta2AR desensitizes upon repeated activation through several mechanisms, including downregulation of the number of beta2AR receptors (reviewed in [30,31]). Indeed, beta2AR expression is more highly expressed at the basal layers of the epidermis and decreases in expression toward the stratum corneum [12], suggesting that epinephrine may be activating the receptor to increase intracellular calcium levels and induce differentiation. However, further studies will be needed to determine how essential the autocrine epinephrine/beta2AR signaling cascade is for keratinocyte differentiation and formation of the epidermal architecture.…”

PP2A Activation by β2-Adrenergic Receptor Agonists

“…In addition to the EGFR, keratinocytes also express high levels of the G-protein-coupled receptor, the ␤ 2 -adrenergic receptor, (␤ 2 -AR) (14,15), whose functional role in the epidermis has not yet been elucidated. Keratinocytes do not express the ␤ 1 -AR (16).…”