CD8+ T cell memory is sustained in mice by hepatic stellate cells

BACKGROUND AND AIMS

Long-lasting immunological memory is the ultimate goal of vaccination. Homeostatic maintenance of memory CD8⁺ cytotoxic T cells (MemCD8TCs) is thought to be mediated by IL-15/IL-15R heterodimer (15HD)-expressing myeloid cells. Nonmyeloid hepatic stellate cells (HSCs) also express 15HD, but their role in maintaining MemCD8TC homeostasis is unknown.

APPROACH AND RESULTS

We engineered a genetically engineered mouse in which IL-15R complementary DNA (cDNA) had been inserted in-frame with lecithin-retinol acyltransferase gene and bred onto an IL-15R-KO (15R-KO) genetic background (L15R) that expressed IL-15R in HSCs at normal levels, but not in other liver cells. Outside of the liver of L15R mice, IL-15R expression was found in a number of organs, but not in dendritic cells and macrophages. The low IL-15R expression in the bone marrow (BM) of L15R mice was eliminated by the reconstitution of lethally-irradiated L15R mice with 15R-KO BM to generate L15RC mice. Because MemCD8TC maintenance is mediated by 15HD, not empty IL-15R, 15HD content in L15R mice was determined and found for liver, lung, kidney, and heart. L15R and L15RC mice developed and maintained long-lasting, systemic antigen-specific MemCD8TCs that were efficacious against tumor growth and Listeria monocytogenes infection in an antigen-specific manner. Among the four organs with 15HD content, liver-associated MemCD8TCs were different from those found in the lung, kidney, and heart in two ways: (1) they were quantitatively the most numerous, and (2) they appeared uniquely in the form of clusters in a specialized structure, sinusoidal niches of the liver.

CONCLUSIONS

The liver, the largest organ of the body, is endowed with the capability of effectuating long-lasting functional cytotoxic T cell memory.

HMG20A Inhibit Adipogenesis by Transcriptional and Epigenetic Regulation of MEF2C Expression

Obesity and its associated metabolic disease do serious harm to human health. The transcriptional cascade network with transcription factors as the core is the focus of current research on adipogenesis and its mechanism. Previous studies have found that HMG domain protein 20A (HMG20A) is highly expressed in the early stage of adipogenic differentiation of porcine intramuscular fat (IMF), which may be involved in regulating adipogenesis. In this study, HMG20A was found to play a key negative regulatory role in adipogenesis. Gain- and loss-of-function studies revealed that HMG20A inhibited the differentiation of SVF cells and C3H10T1/2 cells into mature adipocytes. RNA-seq was used to screen differentially expressed genes after HMG20A knockdown. qRT-PCR and ChIP-PCR confirmed that MEF2C was the real target of HMG20A, and HMG20A played a negative regulatory role through MEF2C. HMG20A binding protein LSD1 was found to alleviate the inhibitory effect of HMG20A on adipogenesis. Further studies showed that HMG20A could cooperate with LSD1 to increase the H3K4me2 of the MEF2C promoter and then increase the expression of MEF2C. Collectively, these findings highlight a role for HMG20A-dependent transcriptional and epigenetic regulation in adipogenesis.

Rapid Death of Follicular B Cells and Burkitt Lymphoma Cells Effectuated by Xbp1s

BCR-mediated tonic signaling is an indispensable requirement for the survival of follicular B (FOB) cells and Burkitt lymphoma (BL) cells. FOB cells of the I-A^12% mutant mouse express unfolded protein response and are extremely short lived. Among the myriad molecules activated by unfolded protein response in I-A^12% B cells, Xbp1s singularly "hijacked" p110 from p85:p110 heterodimeric PI3K, thereby abating BCR tonic signaling, resulting in their extremely short lifespan. Long-lived normal FOB cells became short lived upon ectopic Xbp1s expression. The proapoptotic Xbp1s role in FOB cells starkly contrasts with its antithetical prosurvival function in plasma cells. Also, tonic signaling and clonal expansion, two important functions mediated by the same BCR, operate in independent and distinct manners. Furthermore, concerning the development of new therapeutic treatment of drug-refractory BL patients, our finding of Xbp1s-mediated rapid death of BL cells brings forth a conceptual advancement based on blocking PI3K heterodimer formation rather than inhibition of PI3K enzyme activity.