Epithelial LTβR signaling controls the population size of the progenitors of medullary thymic epithelial cells in neonatal mice

Abstract

The establishment of T cell central tolerance critically relies on the development and maintenance of the medullary thymic epithelial cells (mTECs). Disrupted signaling of lymphotoxin beta receptor (LTβR) results in dramatically reduced mTEC population. However, whether LTβR directly or indirectly control mTECs remains undetermined; how LTβR controls this process also remain unclear. In this study, by utilizing K14-Cre × Ltbrfl/fl conditional knockout (cKO) mice, we show that epithelial intrinsic LTβR was essential for the mTEC development postnatally. Mechanistically, LTβR did not directly impact the proliferation or survival of mTECs; the maturation of mTECs from MHC-IIlo to MHC-IIhi stage was also unaltered in the absence of LTβR; interestingly, the number of mTEC progenitors (Cld3,4hiSSEA-1+) was found significantly reduced in LTβR cKO mice at the neonatal stage, but not at E18.5. Consequently, epithelial deficiency of LTβR resulted in significant defect of thymic negative selection as demonstrated using OT-I and RIP-OVA transgenic mouse system. In summary, our study clarifies the epithelial intrinsic role of LTβR on mTEC development and function; more importantly, it reveals a previously unrecognized function of LTβR on the control of the size of mTEC progenitor population.

Redefining thymus medulla specialization for central tolerance

“…Consistent with the expression pattern of Aire ( Gray et al, 2007 ), Fezf2 was detectable only in mTEC hi cells (not depicted). Thus, although LTβR influences mTEC development and organization ( Boehm et al, 2003 ; Lkhagvasuren et al, 2013 ; Wu et al, 2017 ), it is not required for generation of Fezf2 + mTECs. Rather, RANK represents a key regulator of both Aire + and Fezf2 + mTECs.…”

Altered Maturation of Medullary TEC in EphB-Deficient Thymi Is Recovered by RANK Signaling Stimulation

“…Similar conclusions can be drawn from the analysis of other molecules expressed by mTECs that define different cell subsets ( 39 , 42 – 45 ). It is assumed that committed mTEPCs differentiate to immature MHCII lo mTECs and then to mature MHCII hi mTECs ( 26 , 46 ) although mTEC lo cells also include terminally differentiated mTECs ( 46 ) as well as osteoprotegerin + and osteoprotegerin − cells ( 17 ). Brunk and colleagues ( 47 ) also define an MHCII − CD80 − progenitor cell population capable of upregulating MHCII expression to MHCII lo CD80 − cells that further generate MHCII hi CD80 − cTECs and then MHCII hi CD80 + mTEC.…”

“…Furthermore, there are no changes either in the transcript production of LTβR and RANK in both fetal and PN mutant thymi, two receptors of the TNF receptor superfamily expressed on mTEC and whose involvement in TEC development is clearly recognized although not conclusively understood. LTβR signaling in mTEC seems to control the population size of mTEPCs ( 46 ) and influences mTEC development and organization ( 43 , 46 , 71 ), but its claimed relationship with the Fezf2 transcription factor ( 72 ) is questioned by other authors ( 38 ). Meantime, RANK and CD40 signaling are important for AIRE mTEC development ( 2 ) and, also perhaps for Fezf2 regulation ( 38 ).…”

Lymphotoxin β receptor-mediated NFκB signaling promotes glial lineage differentiation and inhibits neuronal lineage differentiation in mouse brain neural stem/progenitor cells

“…LTα also binds to one or two membrane-associated LTβ to form LTα 2 β 1 and LTα 1 β 2 heterotrimers, respectively [ 46 , 47 ]. The predominant heterotrimer LTα 1 β 2 binds to LTβ receptor (LTβR) primarily expressed on epithelial and stromal cells [ 48 ] and cells of the myeloid lineage [ 49 ]. Most studies on LTβR signaling have focused on the organization, development, and maintenance of lymphoid tissues [ 48 ] and their role in adaptive and innate immune responses [ 50 ].…”

“…The predominant heterotrimer LTα 1 β 2 binds to LTβ receptor (LTβR) primarily expressed on epithelial and stromal cells [ 48 ] and cells of the myeloid lineage [ 49 ]. Most studies on LTβR signaling have focused on the organization, development, and maintenance of lymphoid tissues [ 48 ] and their role in adaptive and innate immune responses [ 50 ]. LTβR signaling modulates follicular dendritic cell maintenance and germinal center formation in lymph nodes [ 51 ].…”