Bone marrow (BM) perivascular stromal cells and vascular endothelial cells (ECs) are essential for hematopoietic stem cell (HSC) maintenance, but the roles of distinct niche compartments during HSC regeneration are less understood. Here we show that Leptin receptor-expressing (LepR+) BM stromal cells and ECs dichotomously regulate HSC maintenance and regeneration via secretion of pleiotrophin (PTN). BM stromal cells are the key source of PTN during steady-state hematopoiesis because its deletion from stromal cells, but not hematopoietic cells, osteoblasts, or ECs, depletes the HSC pool. Following myelosuppressive irradiation, PTN expression is increased in bone marrow endothelial cells (BMECs), and PTN ECs are more frequent in the niche. Moreover, deleting Ptn from ECs impairs HSC regeneration whereas Ptn deletion from BM stromal cells does not. These findings reveal dichotomous and complementary regulation of HSC maintenance and regeneration by BM stromal cells and ECs.

The role of osteolineage cells in regulating hematopoietic stem cell (HSC) regeneration following myelosuppression is not well understood. Here we show that deletion of the pro-apoptotic genes Bak and Bax in osterix (Osx, also known as Sp7 transcription factor 7)-expressing cells in mice promotes HSC regeneration and hematopoietic radioprotection following total body irradiation. These mice showed increased bone marrow (BM) levels of the protein dickkopf-1 (Dkk1), which was produced in Osx-expressing BM cells. Treatment of irradiated HSCs with Dkk1 in vitro increased the recovery of both long-term repopulating HSCs and progenitor cells, and systemic administration of Dkk1 to irradiated mice increased hematopoietic recovery and improved survival. Conversely, inducible deletion of one allele of Dkk1 in Osx-expressing cells in adult mice inhibited the recovery of BM stem and progenitor cells and of complete blood counts following irradiation. Dkk1 promoted hematopoietic regeneration via both direct effects on HSCs, in which treatment with Dkk1 decreased the levels of mitochondrial reactive oxygen species and suppressed senescence, and indirect effects on BM endothelial cells, in which treatment with Dkk1 induced epidermal growth factor (EGF) secretion. Accordingly, blockade of the EGF receptor partially abrogated Dkk1-mediated hematopoietic recovery. These data identify Dkk1 as a regulator of hematopoietic regeneration and demonstrate paracrine cross-talk between BM osteolineage cells and endothelial cells in regulating hematopoietic reconstitution following injury.

Sirt1 is a member of the sirtuin family of proteins and has important roles in numerous biological processes. Sirt1 −/− mice display an increased frequency of abnormal spermatozoa, but the mechanism of Sirt1 in spermiogenesis remains largely unknown. Here, we report that Sirt1 might be directly involved in spermiogenesis in germ cells but not in steroidogenic cells. Germ cell-specific Sirt1 knockout mice were almost completely infertile; the early mitotic and meiotic progression of germ cells in spermatogenesis were not obviously affected after Sirt1 depletion, but subsequent spermiogenesis was disrupted by a defect in acrosome biogenesis, which resulted in a phenotype similar to that observed in human globozoospermia. In addition, LC3 and Atg7 deacetylation was disrupted in spermatids after knocking out Sirt1, which affected the redistribution of LC3 from the nucleus to the cytoplasm and the activation of autophagy. Furthermore, Sirt1 depletion resulted in the failure of LC3 to be recruited to Golgi apparatus-derived vesicles and in the failure of GOPC and PICK1 to be recruited to nucleus-associated acrosomal vesicles. Taken together, these findings reveal that Sirt1 has a novel physiological function in acrosome biogenesis.

Background and Aims Aristolochic acid (AA) exposure has been statistically associated with human liver cancers. However, direct evidence of AA exposure–induced liver cancer is absent. This study aims to establish a direct causal relationship between AA exposure and liver cancers based on a mouse model and then explores the AA‐mediated genomic alterations that could be implicated in human cancers with AA‐associated mutational signature. Approach and Results We subjected mice, including phosphatase and tensin homolog (Pten)‐deficient ones, to aristolochic acid I (AAI) alone or a combination of AAI and CCl4. Significantly, AAI exposure induced mouse liver cancers, including hepatocellular carcinoma (HCC) and combined HCC and intrahepatic cholangiocarcinoma, in a dose‐dependent manner. Moreover, AAI exposure also enhanced tumorigenesis in these CCl4‐treated or Pten‐deficient mice. AAI led to DNA damage and AAI‐DNA adduct that could initiate liver cancers through characteristic adenine‐to‐thymine transversions, as indicated by comprehensive genomic analysis, which revealed recurrent mutations in Harvey rat sarcoma virus oncogene. Interestingly, an AA‐associated mutational signature was mainly implicated in human liver cancers, especially from China. Moreover, we detected the AAI‐DNA adduct in 25.8% (16/62) of paratumor liver tissues from randomly selected Chinese patients with HCC. Furthermore, based on phylogenetic analysis, the characteristic mutations were found in the initiating malignant clones in the AA‐implicated mouse and human liver cancers where the mutations of tumor protein p53 and Janus kinase 1 were prone to be significantly enriched in the AA‐affected human tumors. Conclusions This study provides evidence for AA‐induced liver cancer with the featured mutational processes during malignant clonal evolution, laying a solid foundation for the prevention and diagnosis of AA‐associated human cancers, especially liver cancers.

Genetic heterogeneity of tumor is closely related to its clonal evolution, phenotypic diversity and treatment resistance, and such heterogeneity has only been characterized at single-cell sub-chromosomal scale in liver cancer. Here we reconstructed the single-variant resolution clonal evolution in human liver cancer based on single-cell mutational profiles. The results indicated that key genetic events occurred early during tumorigenesis, and an early metastasis followed by independent evolution was observed in primary liver tumor and intrahepatic metastatic portal vein tumor thrombus. By parallel single-cell RNA-Seq, the transcriptomic phenotype of HCC was found to be related with genetic heterogeneity. For the first time we reconstructed the single-cell and single-variant clonal evolution in human liver cancer, and dissection of both genetic and phenotypic heterogeneity will facilitate better understanding of their relationship.

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Prostate cancer is the most commonly diagnosed type of cancer and the second leading cause of cancer‑associated mortality in males. The efficacy of prostate cancer chemotherapy is frequently impaired by drug resistance; however, the underlying mechanisms of this resistance remain elusive. Sex determining region Y-box 2 (Sox2) is of vital importance in the regulation of stem cell proliferation and carcinogenesis. In the present study, using MTT, clone formation, cell cycle and apoptosis assays, over-expression of Sox2 was demonstrated to enhance the paclitaxel (Pac) resistance of the PC-3 prostate cancer cell line, promoting cell proliferation and exhibiting an anti‑apoptotic effect. Western blot analysis revealed that the phosphoinositide 3-kinase/Akt signaling pathway was activated in cells overexpressing Sox2, and by targeting cyclin E and survivin, Sox2 promoted G1/S phase transition and prevented apoptosis under Pac treatment. The present study provided an understanding of Pac resistance in prostate cancer and may indicate novel therapeutic methods for chemoresistant prostate cancer.