Selective suppression of the long isoform of the prolactin receptor (PRLR) may reduce pathogenic immune-cell activity in samples in patients with systemic lupus erythematosus (SLE) and could prevent early glomerular abnormalities in lupus-prone mice.
In a study, researchers assessed whether abnormal splicing of the PRLR contributes to SLE and whether selectively reducing its long isoform could modify disease-associated immune responses. They combined human immune-cell sequencing datasets as well as tests using peripheral blood mononuclear cells (PBMC) from patients with SLE and healthy donors n female MRL-lpr mice predisposed to lupus. The researchers used splice-modulating oligomers (SMO) designed to decrease expression of the long PRLR isoform while increasing expression of shorter variants.
The researchers evaluated PRLR isoform expression, immune-cell activation and differentiation, type I interferon (IFN-1) signaling, plasma cell populations, and immunoglobulin characteristics associated with autoreactivity. Kidney outcomes included glomerular tuft size, nuclear counts, and cellular density. Human immune-cell experiments included samples from up to 9 patients with SLE and corresponding healthy donors, while kidney histology was assessed in 5 treated and 6 control mice.
Following 8 weeks of treatment, lupus-prone mice receiving the targeted SMO had smaller glomerular tufts, fewer glomerular cell nuclei, and lower glomerular cellular density compared with control-treated mice. All 3 measures showed statistically significant differences, indicating that long PRLR isoform knockdown prevented the development of early glomerular hypercellularity.
The intervention altered immune-cell populations involved in SLE pathogenesis. Single-cell RNA sequencing of spleen samples from 4 treated and 4 control mice showed reductions in pathogenic B-cell and plasma cell populations. Treatment also reduced immunoglobulin transcripts containing sequence characteristics associated with autoreactivity, including changes in plasma cell populations producing potentially autoreactive antibodies.
Additional analyses showed that the intervention affected immune cells both expressing and lacking PRLR, which the researchers interpreted as evidence of direct and indirect effects on disease-associated immune populations. Treatment partially restored gene expression patterns in several B-cell subsets toward those observed in healthy mice.
In human samples, the researchers identified an increased ratio of long to short PRLR transcripts across multiple immune-cell populations in patients with SLE compared with healthy donors. The imbalance was associated with altered immune-cell differentiation and inflammatory signaling.
Following 72 hours of exposure to the targeted SMO, PBMCs from patients with SLE showed reduced B-cell activation and changes in monocyte and natural killer cell differentiation. B-cell activation was assessed in samples from 9 patients with SLE and 8 healthy donors, while monocyte differentiation analyses included 8 patients and 7 healthy donors. Natural killer cell differentiation was evaluated in samples from 9 patients and 9 healthy donors.
The intervention reduced expression of the B-cell activation marker CD69 and shifted monocyte and natural killer cell populations toward more differentiated phenotypes. These effects were observed in samples from patients with SLE, without detectable adverse effects on the viability or measured immune-cell phenotypes of healthy donor samples.
The researchers assessed IFN-related signaling in PBMCs from 3 patients with active SLE. Following 24 hours of treatment, expression of at least 6 of 10 IFN-stimulated genes declined in each sample. Expression of MX1 and IRF1 decreased in all 3 samples, while MX2, IRF7, and STAT1 showed reductions in at least 2 samples.
Consistent with these findings, long PRLR isoform knockdown reduced STAT1 phosphorylation and IFN-1 signaling in experimental models. The authors also observed reductions in immunoglobulin features associated with autoreactivity, suggesting that the intervention affected multiple immune pathways involved in SLE pathogenesis.
Although mean urinary calcium excretion was lower in treated lupus-prone mice, the difference was not statistically significant. The researchers reported that the animals were evaluated before substantial proteinuria typically develops in this model, limiting conclusions about established kidney disease.
Human experiments were conducted outside the body using relatively small samples from previously treated adult female patients, limiting generalizability to other populations. PRLR isoform expression was primarily assessed at the transcript level rather than the protein level because of technical limitations. The mouse experiments examined early glomerular abnormalities rather than long-term renal outcomes or established lupus nephritis. The findings did not establish clinical efficacy, long-term kidney protection, or safety in patients with SLE.
“[Knockdown] of the [long] PRLR represents a potential treatment strategy for SLE that merits further investigation,” wrote lead study author Joao Rodrigues Lima-Junior, PhD, of the Beckman Research Institute of City of Hope in Monrovia, and colleagues.
The study authors declared no conflicts of interest.
