Thymic rejuvenation via FOXN1-reprogrammed embryonic fibroblasts (FREFs) to counteract age-related inflammation.

Jiyoung Oh,Weikan Wang,Rachel Thomas,Dong-Ming Su

doi:10.1172/jci.insight.140313

Abstract

Age-associated systemic, chronic inflammation is partially attributed to increased self-autoreactivity, resulting from disruption of central tolerance in the aged, involuted thymus. This involution causally results from gradually decreased expression of the transcription factor FOXN1 in thymic epithelial cells (TECs), whereas exogenous FOXN1 in TECs can partially rescue age-related thymic involution. TECs induced from FOXN1-overexpressing embryonic fibroblasts can generate an ectopic de novo thymus under the kidney capsule, and intrathymic injection of naturally young TECs can lead to middle-aged thymus regrowth. Therefore, as a thymic rejuvenation strategy, we extended these 2 findings by combining them with 2 types of promoter-driven (Rosa26CreERT and FoxN1Cre) Cre-mediated FOXN1-reprogrammed embryonic fibroblasts (FREFs). We engrafted these FREFs directly into the aged murine thymus. We found substantial regrowth of the native aged thymus with rejuvenated architecture and function in both males and females, exhibiting increased thymopoiesis and reinforced thymocyte negative selection, along with reduced senescent T cells and autoreactive T cell–mediated inflammation in old mice. Therefore, this approach has preclinical significance and presents a strategy to potentially rescue decreased thymopoiesis and perturbed negative selection to substantially, albeit partially, restore defective central tolerance and reduce subclinical autoimmune symptoms in elderly people.

Highlights

Age-related immune dysfunction is generally characterized by 2 extremes: immunosenescence [1] and inflammaging [2, 3]
To confirm whether the observed thymic epithelial cells (TECs) regrew from the native aged thymus when they received stimulation from an iTEC-rejuvenated microenvironment, or if these TECs grew directly from the newly transplanted forkhead box N1 (FOXN1)-reprogrammed embryonic fibroblasts (FREFs), we examined the sources of these TECs in the rejuvenated, aged thymuses based on endogenous and exogenous FoxN1 expression
These increases did not reach the same levels as in young mice (Figure 4C), they significantly increased, compared with naturally aged controls (FTg-only group). These results provided an indication that transplantation of FREFs potentially restores TEC function in negative selection as demonstrated by increased autoimmune regulator (Aire)+ medullary thymic epithelial cell (mTEC) and enhanced negative selection signaling strength in the CD4 single-positive (CD4SP) thymocytes in the aged thymus

Summary

Introduction

Age-related immune dysfunction is generally characterized by 2 extremes: immunosenescence (immune insufficiency) [1] and inflammaging (a chronic, persistent, sterile, systemic inflammation, partially owing to strong self-reactivity) [2, 3]. Immunosenescence, unlike cultured cellular senescence, occurs at systemic levels exhibiting diminished immune reaction in response to antigen stimulations, mainly owing to contracted T cell receptor (TCR) repertoire diversity [9]. This is primarily attributed to a decreased output of naive T cells from the aged, atrophied thymus [10] and expansion of monoclonal memory T cells in the periphery (detailed in our review) [11]. The increased self-reactive T cells in elderly people are derived from perturbed central T cell tolerance establishment [6, 7, 14], owing to defects in negative selection and altered Treg generation [7, 15] in the aged, atrophied thymus

Methods

Results

Conclusion