Prolactin Rescues Immature B Cells from Apoptosis-Induced BCR-Aggregation through STAT3, Bcl2a1a, Bcl2l2, and Birc5 in Lupus-Prone MRL/lpr Mice

Abstract

Self-reactive immature B cells are eliminated through apoptosis by tolerance mechanisms, failing to eliminate these cells results in autoimmune diseases. Prolactin is known to rescue immature B cells from B cell receptor engagement-induced apoptosis in lupus-prone mice. The objective of this study was to characterize in vitro prolactin signaling in immature B cells, using sorting, PCR array, RT-PCR, flow cytometry, and chromatin immunoprecipitation. We found that all B cell maturation stages in bone marrow express the prolactin receptor long isoform, in both wild-type and MRL/lpr mice, but its expression increased only in the immature B cells of the latter, particularly at the onset of lupus. In these cells, activation of the prolactin receptor promoted STAT3 phosphorylation and upregulation of the antiapoptotic Bcl2a1a, Bcl2l2, and Birc5 genes. STAT3 binding to the promoter region of these genes was confirmed through chromatin immunoprecipitation. Furthermore, inhibitors of prolactin signaling and STAT3 activation abolished the prolactin rescue of self-engaged MRL/lpr immature B cells. These results support a mechanism in which prolactin participates in the emergence of lupus through the rescue of self-reactive immature B cell clones from central tolerance clonal deletion through the activation of STAT3 and transcriptional regulation of a complex network of genes related to apoptosis resistance.

Prolactin promotes proliferation of germinal center B cells, formation of plasma cells, and elevated levels of IgG3 anti-dsDNA autoantibodies

“…Thus, we interpretate these data as PRL may not increase the B-GC cell differentiation, but that it may promote an alternative mechanism to increase the number of differentiating B-GCs. PRL can increase the survival of immature B cells in MRL/lpr mice ( 20 ). However, we did not observe an increased survival of PRL-treated B-GCs in the culture conditions ( Figure 3K ).…”

“…PRL is a multifunctional hormone that is essential for the survival and proliferation of different cell types, both immune and nonimmune ( 44 , 45 ). PRL regulates apoptosis by increasing the expression of antiapoptotic genes in both T cells ( 46 ), and immature B cells ( 20 ). Although in immature B cells from MRL/lpr mice, PRL can increase the survival and protect against apoptosis, it did not have this effect on already differentiated mature B cells (B-GCs), even though both cells express the long isoform of the receptor.…”

“…Although in immature B cells from MRL/lpr mice, PRL can increase the survival and protect against apoptosis, it did not have this effect on already differentiated mature B cells (B-GCs), even though both cells express the long isoform of the receptor. This difference may be due to differential signaling pathway activation mediated by PRL at each stage of B-cell maturation, while in immature B cells, it seems to preferentially activate STAT3 ( 20 ). We observed here that it preferentially activates STAT1 in B-GC cells.…”

“…Our group has reported that the different stages of maturation of B cells in bone marrow (proB, preB, and immature) ( 15 ), and in the spleen (transitional, follicular [FO] and marginal zone [MZ]) express the PRL receptor ( 16 ), both in strains that do not develop SLE (C57BL/6) and in models affected by the disease (MRL/lpr). In addition, we identified that PRL influences the B-cell maturation process by rescuing immature autoreactive B cells from apoptosis ( 20 , 21 ). However, the mechanism by which PRL may favor autoantibody production is unclear.…”

The effect of prolactin on immune cell subsets involved in SLE pathogenesis

“…Through these mechanisms, PRL participates in the onset of SLE by rescuing cells destined for clonal deletion. The activation of PRLR could also affect clones of immature autoreactive B cells through STAT3 activation and the transcriptional regulation of apoptosis resistance-related genes in an animal SLE model ( 73 ). This decreased apoptosis may be due to the upregulation of anti-apoptotic BCL-XL gene and a concomitant decrease of Bad expression caused by PRL in the MRL/lpr model ( 74 ).…”