Background Anti-ribosomal P (anti-P) antibodies have long been associated with lupus psychosis and recently with cognitive deficit in patients with systemic lupus erythematosus (SLE). We previously described a neuronal-surface-P-antigen (NSPA) that mediates anti-P pathogenic effects leading to memory deficit in mice. Clinical controversial associations of anti-P are lupus hepatitis and lupus nephritis (LN), in which the ribosomal P0 protein has been postulated as a cell surface anti-P target. As there is no mechanism explaining for the presence of P0 at the cell surface, we assess whether NSPA might be the anti-P cell surface target in liver and kidney cells.

Methods NSPA expression: i) RT-PCR and immunoblot in liver HepG2 and kidney HK-2 cell lines and liver and kidney tissues from C57wt and transgenic C57NSPA/KO (LacZ gene instead NSPA gene) mice; ii) ß-galactosidase histochemistry as a marker of NSPA expression in liver and kidney slices from a ZZEF-1/lac Z knock in mice; iii) Cell surface biotinylation and surface immuno-capture in combination with metabolic labeling. Functional assays: iv) Internalization assays with I125-anti-P; v) Indirect immunofluorescence of activated caspase-3 and Hoechst staining of apoptotic nuclei on HK-2 treated with rabbit anti-P for 24 hour.

Results NSPA is expressed in hepatocytes, in proximal epithelium tubule renal cells and in some collecting tubules. HK-2 and HepG2 express NSPA, but not P0 at the cell surface. Anti-P bind NSPA and become internalized in a time and concentration dependent manner. Anti-P induced HK-2 apoptosis in vitro assessed by caspase-3 activation.

Conclusions NSPA expression in the cell surface of kidney and liver cells and not the P0 provides a potential target for anti-P pathogenic effects, which might contribute to lupus hepatitis and nephritis.

Funding Source(s): Programa de Financiamiento Basal (AFB 17/0005) and FONDECYT N° 1160513.