Crucial Role of Increased Arid3a at the Pre-B and Immature B Cell Stages for B1a Cell Generation

Abstract

The Lin28b+Let7− axis in fetal/neonatal development plays a role in promoting CD5+ B1a cell generation as a B-1 B cell developmental outcome. Here we identify the Let7 target, Arid3a, as a crucial molecular effector of the B-1 cell developmental program. Arid3a expression is increased at pro-B cell stage and markedly increased at pre-B and immature B cell stages in the fetal/neonatal liver B-1 development relative to that in the Lin28b−Let7+ adult bone marrow (BM) B-2 cell development. Analysis of B-lineage restricted Lin28b transgenic (Tg) mice, Arid3a knockout and Arid3a Tg mice, confirmed that increased Arid3a allows B cell generation without requiring surrogate light chain (SLC) associated pre-BCR stage, and prevents MHC class II cell expression at the pre-B and newly generated immature B cell stages, distinct from pre-BCR dependent B development with MHC class II in adult BM. Moreover, Arid3a plays a crucial role in supporting B1a cell generation. The increased Arid3a leads higher Myc and Bhlhe41, and lower Siglec-G and CD72 at the pre-B and immature B cell stages than normal adult BM, to allow BCR signaling induced B1a cell generation. Arid3a-deficiency selectively blocks the development of B1a cells, while having no detectable effect on CD5− B1b, MZ B, and FO B cell generation resembling B-2 development outcome. Conversely, enforced expression of Arid3a by transgene is sufficient to promote the development of B1a cells from adult BM. Under the environment change between birth to adult, altered BCR repertoire in increased B1a cells occurred generated from adult BM. However, crossed with B1a-restricted VH/D/J IgH knock-in mice allowed to confirm that SLC-unassociated B1a cell increase and CLL/lymphoma generation can occur in aged from Arid3a increased adult BM. These results confirmed that in fetal/neonatal normal mice, increased Arid3a at the pre-B cell and immature B cell stages is crucial for generating B1a cells together with the environment for self-ligand reactive BCR selection, B1a cell maintenance, and potential for development of CLL/Lymphoma in aged mice.

An ontogenetic switch drives the positive and negative selection of B cells

“…Two transcription factor targets stabilized by Lin28b and highlighted by our analysis, Arid3a and Bhlhe41, have previously been shown to be critical for B-1 B cell development. Expression of Arid3a tg in adult pro-B cells increases B-1 B cell generation while RNAi-mediated knockdown or conditional inactivation of Arid3a in FL pro-B cells reduces CD5 + B-1a B cell numbers in the peritoneum (17,42). The transcription factor Bhlhe41, previously identified as highly expressed in mature B-1a B cells (17), is also required for B-1 B cell generation and, possibly, survival, since B-1a cells are reduced in Bhlhe41and Bhlhe40/ Bhlhe41-deficient mice (12).…”

“…The way in which differences in B cell development or ancillary signals during B-1 B cell development in early ontogeny might compensate for reduced IL-7-dependent signaling is unknown, but positive selection at the pre-BCR stage might be an important factor. While adult B cell development requires pre-BCR signaling, some autoreactive HC associated with B-1a B cell development, including VH11 PtC-specific HC, do not need to associate with SLC to support B-1a cell development, provided they coexpress Lin28b or downstream Arid3a (42). In adult BM, an autoreactive anti-MHC class I 3-83 BCR HC and LC tg targeted to the endogenous loci can also support B cell development in the absence of SLC but in the presence of the cognate MHC self-antigen (46).…”

New Frontiers: ARID3a in SLE

“…Although most ARID family members are expressed ubiquitously, ARID3a expression is tissue and developmentally restricted to hematopoietic and other adult stem cells, and to particular types of mature cells in the hematopoietic lineage [19]. The expression of ARID3a is tightly regulated during B cell development in both mice and humans, and is the highest in the bone marrow pre-B and germinal center-activated B cells, while other B cell subsets, including the majority of mature splenic B cells, lack both ARID3a mRNA and protein [20,21]. During B lymphocyte development in mice, ARID3a expression is tightly regulated, such that it is expressed in transitional T1 B cells, down-regulated at the T2 cell stage where tolerance checkpoints have been identified [22,23], and turned off at the level of transcription in naïve follicular B cells [24,25].…”

“…During B lymphocyte development in mice, ARID3a expression is tightly regulated, such that it is expressed in transitional T1 B cells, down-regulated at the T2 cell stage where tolerance checkpoints have been identified [22,23], and turned off at the level of transcription in naïve follicular B cells [24,25]. Others have shown recently that ARID3a is required for fetal lineage B1 B cell development [21,26]. ARID3a is also expressed in mature B1 and marginal-zone (MZ) B cells, two cell types associated with autoimmunity in several systems [24,27,28,29,30,31].…”

TLR engagement induces ARID3a in human blood hematopoietic progenitors and modulates IFNα production

“…Although forced expression of ARID3a in total cord blood HSPCs lead to B lymphoid versus myeloid development [ 4 ] and ARID3a is necessary for B1 lineage development in mice [ 4 , 33 , 34 ], increasing ARID3a levels in circulating adult HSPCs via CpG stimulation prior to culture initiation did not increase B lineage development. Rather, all TLR stimuli resulted in increases in myeloid cell development, consistent with previous observations by others [ 1 , 3 , 20 ].…”