Background: Aldosterone producing cell clusters (APCCs) are microscopic pockets of cells in the adrenal zona glomerulosa (ZG), which stain densely for aldosterone synthase (CYP11B2). They exist in 30% of normal adrenal glands and have similar somatic genetic mutations as some aldosterone producing adenomas (APA), especially of CACNA1D. Some APCCs are precursors to APAs. Adrenalectomy for primary aldosteronism (PA) cures hypertension in < 50% of patients, maybe because of APCCs in the contralateral gland. A potential surface marker of APCCs is SLC35F1: a mainly neuronal decamembrane-spanning nucleotide sugar transporter. Structural similarity suggests a possible role as nicotinamide transporter, reflecting high NADPH requirements in steroidogenesis. Microarray data demonstrated exquisitely selective upregulation of SLC35F1 mRNA in APCCs, and Wnt-activated APAs (with CTNNB1 mutations), but not in surrounding ZG.
Methods: 4µm sections of paraffin embedded normal and para-APA adrenal tissue were stained using Gomez-Sanchezs monoclonal antiserum to CYP11B2 and, on serial sections, of polyclonal anti-SLC35F1 (Novus NBP1-86755). HEK293 cells were transfected with GFP-tagged SLC35F1 to study subcellular localisation, as a prelude to 3H-nicotinamide uptake experiments.
Results: There was strong staining of CYP11B2 in clusters of cells in ZG, consistent with APCCs, in all adrenal glands adjacent to ZG-like APAs (n=9) except for 3 adrenals adjacent to CTNNB1-mutant APAs. Serial sections showed exquisite positive staining for SLC35F1 in APCCs, with no staining in surrounding ZG, ZF or ZR. Staining appeared membranous, but in transfected HEK293 cells was more variable.
Conclusions: SLC35F1 is abundantly and selectively expressed in APCCs. Recent studies in other cell-types have suggested endosomal shuttling of SLC35F1, possibly consistent with our findings in transfected cells. Localisation to plasma membrane in APCCs would enable antibody separation of APCC cells from primary adrenal cultures and provide a target for novel therapies which selectively inhibit autonomous aldosterone production. Its functional role is now under investigation.