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Background Adipocyte accumulation is a predominant feature of age-related thymic involution, but the mechanisms responsible for thymic adipogenesis remain to be elucidated. The aim of this study was to identify key regulators in thymic adipogenesis. We used rosiglitazone, a potent peroxisome proliferator-activated receptor γ (PPARγ) agonist, to induce adipogenic differentiation of OP9-DL1 cells, and investigated the differentially expressed proteins during adipogenic differentiation by using label-free quantitative proteomics. Furthermore, the effects of transforming growth factor β1 (TGF-β1) on rosiglitazone-induced adipogenic differentiation of OP9-DL1 cells as well as the underlying mechanisms were also investigated. Results Proteomic analysis identified 139 proteins differed significantly in rosiglitazone-treated cells compared with dimethyl sulphoxide (DMSO)-treated cells. Rosiglitazone-induced adipogenic differentiation was inhibited by TGF-β1 treatment in OP9-DL1 cells and primary thymic stromal cells. Real-time PCR analysis showed significant increases in PPARγ and fatty acid binding protein 4 mRNA levels in rosiglitazone-treated cells, which were inhibited by TGF-β1 treatment. TGF-β1 down-regulated PPARγ expression at both mRNA and protein levels in OP9-DL1 cells. Chromatin immunoprecipitation analysis demonstrated that TGF-β1 enhanced the binding of Smad2/3 and histone deacetylase 1, but reduced the binding of H3K14ac to the promoter of PPARγ gene. TGF-β1 partially reversed the inhibitory effects of rosiglitazone on the expression of Axin2 and β-catenin protein levels. TGF-β1 inhibited rosiglitazone-induced adipogenic transformation in OP9-DL1 cells by down-regulation of PPARγ and activation of the canonical Wnt/β-catenin signaling pathway. Conclusion Taken together, activation of TGF-β pathway may serve as a useful strategy to prevent thymic adiposity in age-related thymic involution. Electronic supplementary material The online version of this article (10.1186/s13578-019-0311-1) contains supplementary material, which is available to authorized users.

Adipocyte deposition is a key feature of age-related thymic involution, but the underlying mechanisms responsible for thymic adiposity remain to be elucidated. In the present study, we utilized rosiglitazone, a potent peroxisome proliferator-activated receptor γ agonist, to induce adipogenic differentiation of OP9-DL1 cells, and detected the metabolomics alterations during adipogenic differentiation by using liquid chromatography-mass spectrometry. The obtained metabolites were further processed by multivariate statistical analysis, including principal component analysis, partial least squares discriminant analysis, and orthogonal projection on latent-structures discriminant analysis. As a result, we identified a total of 33 significantly differential metabolites between dimethyl sulphoxide- and rosiglitazone-treated OP9-DL1 cells, which were closely related to the dysregulation of phospholipid metabolism pathway, oxidative stress, and associated amino acid metabolism. Meanwhile, two pathways including glycerophospholipid metabolism and nitrogen metabolism were significantly perturbed (P

D-Galactose (D-Gal) promotes accumulation of reactive oxygen species and formation of advanced glycation end-products, ultimately resulting in oxidative stress. D-Gal has been widely used to induce accelerated aging in anti-aging medical research. Although thymic epithelial cells are particularly sensitive to oxidative stress, there are few reports on the thymus changes accompanying D-Gal-induced aging in mice. To study the effect of D-Gal on rodent thymus, we investigated the degree of thymus atrophy and changes in the atrophy relative index in C57BL/6J mice following subcutaneous injection of D-Gal at different doses (200, 500, 1000 mg/kg per day) for 60 days. Compared with the vehicle-treated (0.9% saline) and young controls, D-Gal at doses of 500 and 1000 mg/kg per day led to a significant thymic atrophy; the latter dose caused atrophy similar to that observed in naturally aged (18-20-month-old) mice. Mice treated with high-dose D-Gal exhibited greater immunosenescence, defective central immune tolerance, increased levels of activated splenic immune cell, and chronic low-grade inflammation, i.e., outcomes similar to those observed in natural aging in mice. Taken together, our results indicate that mice treated with high-dose D-Gal may be a valid model for studying induced thymic atrophy and effects of aging on the immune system.

The influence and underlying mechanisms of human adipose-derived stem cells (Hu-ADSCs) on breast cancer cells in the tumor microenvironment remain unclear. Understanding the association between Hu-ADSCs and cancer cells may provide targets for breast cancer treatment and reference for the clinical application of stem cells. Therefore, a Hu-ADSC and breast cancer MCF7 cell coculture system was established to investigate the paracrine effects of Hu-ADSCs on MCF7 cell migration and invasion, in addition to the potential mechanism of action by reverse transcription-quantitative polymerase chain reaction and western blotting. Hu-ADSCs enhanced MCF7 cell migration and invasion by decreasing the expression of epithelial marker E-cadherin, and increasing the expression of interstitial marker N-cadherin and epithelial-mesenchymal transition (EMT) transcription factors in vitro. The EMT effect of cocultured MCF7 cells was inhibited with the addition of anti-transforming growth factor (TGF)-β1 or phosphoinositide 3-kinase (PI3K) inhibitor LY294002, accompanied by a significant decrease in phosphorylated (p)-mothers against decapentaplegic homolog (Smad) and p-protein kinase B (AKT) expression. The data suggested that the paracrine effect of Hu-ADSCs in the tumor microenvironment promoted the EMT of MCF7 cells by cross interacting with the TGF-β/Smad and PI3K/AKT pathways.

Adipocyte deposition is believed to be a primary characteristic of age-related thymic involution. Herein, we cultured primary thymic stromal cells (TSCs), used rosiglitazone, a potent peroxisome proliferator-activated receptor γ (PPARγ) agonist, to induce adipogenic differentiation, and investigated the differentially expressed genes during adipogenic differentiation by using RNA-sequencing analysis. Furthermore, the effects of Notch1 on rosiglitazone-induced adipogenic differentiation of TSCs as well as the underlying mechanisms were also investigated. As a result, we identified a total of 1737 differentially expressed genes, among which 965 genes were up-regulated and 772 genes were down-regulated in rosiglitazone-treated cells compared with control cells. Gene ontology (GO) enrichment analysis showed that the GO terms were enriched in metabolic process, intracellular, and protein binding. Kyoto encyclopedia of genes and genomes (KEGG) analysis showed that a number of pathways, including ubiquitin mediated proteolysis, PPAR signaling pathway, and mammalian target of rapamycin (mTOR) signaling pathway were predominantly over-represented. Meanwhile, overexpression of Notch1 suppressed and inhibition of Notch1 promoted rosiglitazone-induced adipogenic differentiation in TSCs, and the pro-adipogenic effects of the Notch inhibitor DAPT were associated with the activation of autophagy. Taken together, our results suggest that Notch1 is a key regulator in thymic adipogenesis and may serve as a potential target to hinder thymic adiposity in age-related thymic involution.

Age-related thymic involution is characterized by a loss of thymic epithelial cells (TECs) and a concomitant increase in adipocytes, but the mechanisms involved in thymic adipogenesis are still not clear. Transforming growth factor β1 (TGF-β1) is a pleiotropic cytokine that has been reported to be up-regulated with age in thymic stromal cells in both human and mouse. However, the exact role of TGF-β1 in age-related thymic involution remains to be further elucidated. On the basis of previous findings, we propose a novel hypothesis that TGF-β1 functions a dual role in age-related thymic involution. On one hand, up-regulation of TGF-β1 promotes epithelial to mesenchymal transition (EMT) process in TECs via activating forkhead box protein C2 (FoxC2). On the other hand, TGF-β1 inhibits the transdifferentiation of EMT-derived mesenchymal cells to adipocytes in the thymus. If confirmed, our hypothesis will not only provide further evidence supporting that the transdifferentiation of TECs into pre-adipocytes represents a source of thymic adiposity during age-related thymic involution, but also uncover a unique role of TGF-β1 in the transdifferentiation of TECs into pre-adipocytes. Collectively, the inhibition of TGF-β1 may serve as a strategy to hinder age-related thymic involution or even to restore thymic function in the elderly.

The thymus is a central lymphoid organ that is responsible for T-lymphocyte development and maturation. Through negative and positive selection, lymphoid progenitor cells, which initiate from the bone marrow, develop into mature T cells in the thymus, and are subsequently involved in peripheral cell immunity. It has been reported that the Wnt signaling pathway exists widely in thymic epithelial cells and T lymphocytes. Wnt signaling affects the shape and function of thymic epithelial cells and has an important role in maintaining pro‑T‑cells, and in the subsequent T‑cell differentiation. Previous studies have demonstrated that the Wnt signaling pathway participates in age‑associated thymic involution. In the present study alterations in proliferation and apoptosis were investigated in murine thymic cells during aging. The results of the present study demonstrated that the aged thymus was characterized by markedly decreased cell numbers, as well as decreased proliferation and increased apoptosis. Concurrently, age‑associated changes in thymic cell number and function were accompanied by a decrease in the transcription levels of Wnt4, and downregulation of forkhead box N1 and B‑cell lymphoma‑extra large, which are two target genes of the Wnt4 signaling pathway. In vitro studies demonstrated that activation of the Wnt4 signaling pathway promotes mouse thymus epithelial cell 1 (MTEC1) cell proliferation, and that Wnt4 signaling modulation alleviates dexamethasone‑mediated MTEC1 cell apoptosis. These results suggest that normal expression levels of Wnt4 have a critical role in maintaining the balance between cell proliferation and apoptosis. Alterations in the Wnt signaling pathway may disrupt the epithelial network structure of the thymus, eventually leading to microenvironmental damage. Therefore, further studies regarding the effects of the Wnt signaling pathway on thymus development and age-related thymic involution, may be beneficial for improving the health conditions of the elderly.

Adipocyte deposition is a key feature of age-related thymic involution, but the underlying mechanisms responsible for thymic adiposity remain to be elucidated. In the present study, we utilized rosiglitazone, a potent peroxisome proliferator-activated receptor γ agonist, to induce adipogenic differentiation of OP9-DL1 cells, and detected the metabolomics alterations during adipogenic differentiation by using liquid chromatography-mass spectrometry. The obtained metabolites were further processed by multivariate statistical analysis, including principal component analysis, partial least squares discriminant analysis, and orthogonal projection on latent-structures discriminant analysis. As a result, we identified a total of 33 significantly differential metabolites between dimethyl sulphoxide- and rosiglitazone-treated OP9-DL1 cells, which were closely related to the dysregulation of phospholipid metabolism pathway, oxidative stress, and associated amino acid metabolism. Meanwhile, two pathways including glycerophospholipid metabolism and nitrogen metabolism were significantly perturbed (P 0.05). Collectively, our results may provide some heuristic guidance for addressing the underlying mechanism of thymic adipogenesis, and future studies are warranted to unravel the functions of these altered metabolites in thymic adipogenesis.

Age-related thymic involution is accompanied by a decrease in thymopoiesis and, thus, a deficiency in T cell-mediated immunity in the elderly. A number of events involved in thymic involution have been discovered; however, it remains unclear as to whether they are causes or consequences of thymic involution. These events include the degeneration of T cell progenitors, as well as the deterioration of the thymic stroma, which is a characteristic of thymic epithelial cell loss due to increased apoptosis and decreased cell proliferation. MicroRNAs (miRNAs) are believed to play important roles in the regulation of cell death and proliferation during the aging process. In the present study, we compared the transcriptional levels of various miRNAs in TECs from young and aged mice using microarray analysis. Quantitative PCR was performed to confirm the changes in the expression of miRNAs in the different age groups. Possible downstream targets and pathways of these miRNAs were predicted by performing bioinformatics analysis. To the best of our knowledge, this is the first study to systematically analyze the expression of miRNAs in mouse TECs and to demonstrate that miRNA expression is altered with thymic aging.

Feng Chi, Rong Wu, Xueying Jin, Min Jiang, Xike Zhu Department of Medical Oncology, Shengjing Hospital of China Medical University, Shenyang, People’s Republic of China Abstract: HER2 positivity has been well studied in various cancers, but its importance in non-small-cell lung cancer (NSCLC) is still being explored. In this study, quantitative reverse transcription polymerase chain reaction (qRT-PCR) was performed to detect HER2 and COX-2 expression in NSCLC tissues. Then, pcDNA3.1-HER2 was used to overexpress HER2, while HER2 siRNA and COX-2 siRNA were used to silence HER2 and COX-2 expression. MTT assay and invasion assay were used to detect the effects of HER2 on cell proliferation and invasion. Our study revealed that HER2 and COX-2 expression were upregulated in NSCLC tissues and HER2 exhibited a significant positive correlation with the levels of COX-2 expression. Overexpression of HER2 evidently elevated COX-2 expression, while silencing of HER2 evidently decreased COX-2 expression. Furthermore, overexpressed HER2 induced the ERK phosphorylation, and this was abolished by the treatment with U0126, a pharmacological inhibitor of MEK, an upstream kinase of ERK. HER2-induced expression and promoter activity of COX-2 were also suppressed by U0126, suggesting that the MEK/ERK signaling pathway regulates COX-2 expression. In addition, HER2 induced activation of AKT signaling pathway, which was reversed by pretreatment with U0126 and COX-2 siRNA. MTT and invasion assays revealed that HER2 induced cell proliferation and invasion that were reversed by pretreatment with U0126 and COX-2 siRNA. In this study, our results demonstrated for the first time that HER2 elevated COX-2 expression through the activation of MEK/ERK pathway, which subsequently induced cell proliferation and invasion via AKT pathway in NSCLC tissues. Keywords: HER2, MEK/ERK, COX-2, AKT signaling pathway, non-small-cell lung cancer

It has been speculated that aging lymphohematopoietic progenitor cells (LPC) including hematopoietic stem cells (HSC) and early T-cell progenitors (ETP) have intrinsic defects that trigger age-related thymic involution. However, using a different approach, we suggest that that is not the case. We provided a young thymic microenvironment to aged mice by transplanting a fetal thymus into the kidney capsule of aged animals, and demonstrated that old mouse-derived LPCs could re-establish normal thymic lymphopoiesis and all thymocyte subpopulations, including ETPs, double negative subsets, double positive, and CD4(+) and CD8(+) single positive T cells. LPCs derived from aged mice could turn over young RAG(-/-) thymic architecture by interactions, as well as elevate percentage of peripheral CD4(+)IL-2(+) T cells in response to costimulator in aged mice. Conversely, intrathymic injection of ETPs sorted from young animals into old mice did not restore normal thymic lymphopoiesis, implying that a shortage and/or defect of ETPs in aged thymus do not account for age-related thymic involution. Together, our findings suggest that the underlying cause of age-related thymic involution results primarily from changes in the thymic microenvironment, causing extrinsic, rather than intrinsic, defects in T-lymphocyte progenitors.

Aging is associated with reduced numbers of all thymocyte sub-populations, including early T-cell progenitors. However, it is unclear if this is due to inadequate recruitment of lymphohematopoietic progenitor cells (LPCs) to the aged thymus or to abnormal development of T cells within the thymus. We found that LPCs from young mice were recruited equally well to the thymi of young or aged mice and that thymic stromal cells (TSCs) from young and old mice expressed similar levels of P-selectin and CCL25, which are believed to mediate recruitment of LPCs to the adult thymus. However, the number of recruited thymocytes in old thymus was markedly reduced after two weeks, indicating that T-cell development or proliferation is defective in the aged thymus. We also found that LPCs from aged and young mice have similar capacities to seed a fetal thymus that was transplanted under the kidney capsule. Thymic epithelial cells (TECs) in aged mice had lower proliferative capacity and higher rate of apoptosis, compared with findings in young animals. In addition, immunofluorescence staining with antibodies to cortical and medullary TECs revealed that aged thymi had a disorganized thymic stromal architecture, combined with reduced cellularity of the medulla, and apoptosis of thymocyte sub-populations in the medullary microenvironment was increased, compared with that in young mice. We conclude that aging does not impair recruitment of LPCs to the thymus, but is characterized by abnormalities in thymic epithelial architecture, especially medullary TEC function that may provide sub-optimal support for thymic development of LPCs.

Human 11p15.5, as well as its orthologous mouse 7F4/F5, is known as the imprinting domain extending from IPL/Ipl to H19. OBPH1 and Obph1 are located beyond the presumed imprinting boundary on the IPL/Ipl side. We determined full-length cDNAs and complete genomic structures of both orthologues. We also investigated their precise imprinting and methylation status. The orthologues resembled each other in genomic structure and in the position of the 5' CpG island and were expressed ubiquitously. OBPH1 and Obph1 were predominantly expressed from the maternal allele only in placenta, with hypo- and not differentially methylated 5' CpG islands in both species. These results suggested that the imprinting domain would extend beyond the presumed imprinting boundary and that methylation of the 5' CpG island was not associated with the imprinting status in either species. It remains to be elucidated whether the gene is under the control of the KIP2/LIT1 subdomain or is regulated by a specific mechanism. Analysis of the precise genomic sequence around the region should help resolve this question.

WT2 is defined by a maternal-specific loss of heterozygosity on human chromosome 11p15.5 in Wilms' and other embryonal tumors. Therefore, the imprinted genes in this region are candidates for involvement in Wilms' tumorigenesis. We now report a novel imprinted gene, KCNQ1DN (KCNQ1 downstream neighbor). This gene is located between p57(KIP2) and KvLQT1 (KCNQ1) of 11p15.5 within the WT2 critical region. KCNQ1DN is imprinted and expressed from the maternal allele. We examined the expression of KCNQ1DN in Wilms' tumors. Seven of eighteen (39%) samples showed no expression. In contrast, other maternal imprinted genes in this region, including p57(KIP2), IMPT1, and IPL exhibited almost normal expression in these samples, although some samples expressed IGF2 biallelically. These results suggest that KCNQ1DN existing far from the H19/IGF2 region may play some role in Wilms' tumorigenesis along with IGF2.

A novel gene, C11orf2, was identified by BLAST search in the human chromosome 11p15.5 region potentially responsible for Beckwith–Wiedemann Syndrome (BWS) and some cancers. Two cDNA clones with different sizes were obtained, which share a potential ORF of 399 bp and are different in their 3′ untranslated regions. This gene was revealed to be expressed exclusively in human heart and in almost no other tissues examined by northern blotting. Two transcripts of different sizes, 0.9 and 3.1 kb, were identified in heart, consistent with the length of the two cDNA clones. The gene shows biallelic expression (non-imprinted) in fetal liver, although it is located in the imprinted domain of 11p15.5. C11orf21 codes a protein of 132 amino acids as proved by the expression of C11orf21–EGFP fusion protein in cultured cells. The EGFP-fusion protein expressed in cultured cells localized mainly in the cytoplasm.

A new genetic locus, epi-1, has been identified and mapped, which affects epithelialization of various tissues in the nematode, Caenorhabditis elegans. Seven independent epi-1 mutant alleles have been obtained. These mutants have a wide spectrum of abnormalities, all seem to be caused by a primary defect of basement membrane. We have identified the epi-1 gene as a structural gene of laminin alpha chain. The sequence analyses of the gene and cDNAs revealed that the gene consists of 15 exons and encodes a protein of 3704 amino acids in an open reading frame of 11115 base pairs. The nematode alpha chain is similar to its vertebrate and fly orthologs in the domain structure. The mRNA is trans-spliced to SL1 leader RNA as many of the nematode mRNAs. Mutation sites have been identified in four alleles. Two alleles have nonsense mutations and produce truncated proteins lacking the domain necessary for the formation of a heterotrimeric laminin molecule. The other two alleles have missense mutations in domains VI and IIIb, respectively.

Introduction: During bladder tumorigenesis, thymopoiesis is usually downregulated. Considering that the thymus is the site of most T-cell development, this phenomenon may be related to thymic involution. However, the mechanisms involved in this phenomenon remain to be elucidated. Materials and Methods: An MB 49 murine bladder tumor model was used to identify mechanisms that might underlie this process. Results: The thymuses of tumor-bearing mice showed less cellularity than those of healthy mice. Involution was found to be associated with less proliferation and more apoptosis of thymic epithelial cells (TEC). Foxn1, KGF, and IL-7, three factors known to be involved in thymic development, were also downregulated in the thymuses of tumor bearers. When these mice were intravenously injected with KGF, the thymic microenvironment, thymopoiesis, and T-cell differentiation all returned to near normal status. Conclusions: The decreases in thymopoiesis and impaired T-cell differentiation may be attributable to changes in the thymic microenvironment. Improving the function of TEC, rather than T-cell progenitors, should be the focus of therapy.

A cDNA and a gene encoding the nematode (C. elegans) ribosomal protein L3 have been cloned and sequenced. The nearly full-length cDNA is 1255 bp in size except for the poly (A) tail. The encoded protein consists of 401 amino acids and has calculated molecular weight of 45,657 daltons. The gene sequence determined is 1649 bp and consists of four exons. The sequence of the nematode protein shows high homology to other eukaryotic proteins.

Background The aim of this study was to determine the clinicopathological features of gastric cancers with loss of imprinting (LOI) of LIT1. Insulin-like growth factor 2 (IGF2) and H19 in Chinese patients. Methods DNA and RNA from tumours were amplified and then digested with RsaI, ApaI and HinfI, and RsaI respectively to determine the LOI status. The demographic and clinicopathological characteristics in LOI positive and LOI negative patients were compared and tested with Statistical analysis. Results Of the 89 patients enrolled for analysis, 22, 40 and 35 were heterozygous and thus informative for LIT1, IGF2 and H19 LOI analyses respectively. The positive rate of LIT1, IGF2 and H19 LOI of gastric cancer tissues were 54.6% (12/22), 45% (18/40) and 8.6% (3/32) in Chinese patients. Gastric corpus cancer (8/10, 80%) were more likely to have LOI of IGF2 in tumours than antrum cancers (10/30, 33.3%){odds ratio (OR) = 8, 95% confidence intervals (CI) = 1.425-44.920, p = 0.018)}. LOI of IGF2 in tumours was also associated with the lymph node metastasis (LNM) (OR = 4.5, 95% CI = 1.084-18.689, p = 0.038). Conclusion IGF2 LOI is present in high frequency in Chinese gastric cancer patients, especially those with gastric corpus cancer.

Mouse chromosome 7F4/F5 is a syntenic locus of human 11p15.5 in which many imprinted genes are clustered. Transmission of aberrant human 11p15.5 or duplicated 11p causes Beckwith-Wiedemann syndrome (BWS) depending on which parent the chromosome is derived from. To analyze a syntenic mouse locus corresponding to human 11p15.5, mouse BAC contigs were constructed between Nap2 and Tapa1, in which 390 kb was sequenced between Kvlqt1 and Tapa1. An unexpected finding was that of highly conserved intronic sequences of Kvlqt1 between mouse and human, and their homologies came up to at least 160 kb because the length of this gene extended to 350 kb, suggesting the possibility of some functional constraint due to transcriptional and/or post-transcriptional regulation of this region. Many expressed sequence tags (ESTs) were mapped on this locus. Three genes, Lit1 (Kvlqt1-AS), Mtr1 and Tssc4, were identified and characterized. Lit1 is an antisense-transcript of Kvlqt1 and paternally expressed and maternally methylated throughout the developmental stage. The position where Lit1 exists corresponded to a highly conserved region between mouse and human. This transcript extends at least 60 kb from downstream to upstream of exon 10 in Kvlqt1. Tssc4 and Mtr1 carried putative open reading frames but neither was imprinted. Further characterization of this locus based on the sequence comparison between mouse and human will contribute valuable information towards resolving the mechanism of the occurrence of BWS and the associated childhood tumor.

p57KIP2 is a potent tight-binding inhibitor of several G1 cyclin/cyclin-dependent kinase (Cdk) complexes, and is a negative regulator of cell proliferation. The gene encoding p57KIP2 is located at 11p15.5, a region implicated in both sporadic cancers and Beckwith-Wiedemann syndrome (BWS). Previously we demonstrated that p57KIP2 is imprinted and only the maternal allele is expressed in both mice and humans. We also showed mutations found in p57KIP2 in patients with BWS that were transmitted from the patients' carrier mothers, indicating that the expressed maternal allele was mutant and that the repressed paternal allele was normal. In the study reported here, we performed functional analysis of the two mutated p57KIP2 genes. We showed that the nonsense mutation found in the Cdk inhibitory domain in a BWS patient rendered the protein inactive with consequent complete loss of its role as a cell cycle inhibitor and of its nuclear localization. We also showed that the mutation in the QT domain, although completely retaining its cell cycle regulatory activity, lacked nuclear localization and was thus prevented from performing its role as an active cell cycle inhibitor. Consequently, no active p57KIP2 would have existed, which might have caused the disorders in BWS patients.

Previous reports suggested that aging early T-lymphocyte progenitors (ETPs) derived from bone marrow (BM) hematopoietic stem cells (HSCs) have an intrinsic defect and insufficiency in aged thymus, which triggers age-related thymic involution, but our studies suggest otherwise. We grafted fetal thymus into a kidney capsule of the aged mice, in which aging HSCs could fully generate all thymocyte subpopulations and restore normal thymopoiesis under intact physiological conditions in aged animals. We found that aging ETPs were not deficient initially because both BM HSC and early-stage ETPs—DN1a absolute cell numbers were not significantly reduced although late-stage ETPs—DN1b cells significantly decreased. Moreover, proliferation of the aging ETPs remained unchanged although their apoptotic rate increased. Conversely, provision of sufficient young HSCs/ETPs intravenously or intrathymically failed to restore thymopoiesis in aging host mice. Meanwhile, we demonstrated that young progenitors could seed young and aged thymi without significant difference via intravenous injection. The results exclude insufficient and defective HSCs/ETPs as causes for age-related thymic involution. Our findings indicate that an intrinsic defect in aging T-lymphocyte progenitors is unlikely and HSCs are not synchronal defective with age-related thymic involution during murine aging. (This work was supported by US NIH grant R21AI064939 to DMS).