Induced-Pluripotent-Stem-Cell-Derived Primitive Macrophages Provide a Platform for Modeling Tissue-Resident Macrophage Differentiation and Function.

Tissue macrophages arise during embryogenesis from yolk-sac (YS) progenitors that give rise to primitive YS macrophages. Until recently, it has been impossible to isolate or derive sufficient numbers of YS-derived macrophages for further study, but data now suggest that induced pluripotent stem cells (iPSCs) can be driven to undergo a process reminiscent of YS-hematopoiesis in vitro. We asked whether iPSC-derived primitive macrophages (iMacs) can terminally differentiate into specialized macrophages with the help of growth factors and organ-specific cues. Co-culturing human or murine iMacs with iPSC-derived neurons promoted differentiation into microglia-like cells in vitro. Furthermore, murine iMacs differentiated in vivo into microglia after injection into the brain and into functional alveolar macrophages after engraftment in the lung. Finally, iPSCs from a patient with familial Mediterranean fever differentiated into iMacs with pro-inflammatory characteristics, mimicking the disease phenotype. Altogether, iMacs constitute a source of tissue-resident macrophage precursors that can be used for biological, pathophysiological, and therapeutic studies.

Residual embryonic cells as precursors of a Barrett's-like metaplasia.

Barrett's esophagus is an intestine-like metaplasia and precursor of esophageal adenocarcinoma. Triggered by gastroesophageal reflux disease, the origin of this metaplasia remains unknown. p63-deficient mice, which lack squamous epithelia, may model acid-reflux damage. We show here that p63 null embryos rapidly develop intestine-like metaplasia with gene expression profiles similar to Barrett's metaplasia. We track its source to a unique embryonic epithelium that is normally undermined and replaced by p63-expressing cells. Significantly, we show that a discrete population of these embryonic cells persists in adult mice and humans at the squamocolumnar junction, the source of Barrett's metaplasia. We show that upon programmed damage to the squamous epithelium, these embryonic cells migrate toward adjacent, specialized squamous cells in a process that may recapitulate early Barrett's. Our findings suggest that certain precancerous lesions, such as Barrett's, initiate not from genetic alterations but from competitive interactions between cell lineages driven by opportunity.

Distal airway stem cells yield alveoli in vitro and during lung regeneration following H1N1 influenza infection.

The extent of lung regeneration following catastrophic damage and the potential role of adult stem cells in such a process remains obscure. Sublethal infection of mice with an H1N1 influenza virus related to that of the 1918 pandemic triggers massive airway damage followed by apparent regeneration. We show here that p63-expressing stem cells in the bronchiolar epithelium undergo rapid proliferation after infection and radiate to interbronchiolar regions of alveolar ablation. Once there, these cells assemble into discrete, Krt5+ pods and initiate expression of markers typical of alveoli. Gene expression profiles of these pods suggest that they are intermediates in the reconstitution of the alveolar-capillary network eradicated by viral infection. The dynamics of this p63-expressing stem cell in lung regeneration mirrors our parallel finding that defined pedigrees of human distal airway stem cells assemble alveoli-like structures in vitro and suggests new therapeutic avenues to acute and chronic airway disease.

In vitro and in vivo correlates of physiological and neoplastic human Fallopian tube stem cells.

High-grade serous cancer (HGSC) progresses to advanced stages without symptoms and the 5-year survival rate is a dismal 30%. Recent studies of ovaries and Fallopian tubes in patients with BRCA1 or BRCA2 mutations have documented a pre-metastatic intramucosal neoplasm that is found almost exclusively in the Fallopian tube, termed 'serous tubal intraepithelial carcinoma' or STIC. Moreover, other proliferations, termed p53 signatures, secretory cell outgrowths (SCOUTs), and lower-grade serous tubal intraepithelial neoplasms (STINs) fall short of STIC but share similar alterations in expression, in keeping with an underpinning of genomic disturbances involved in, or occurring in parallel with, serous carcinogenesis. To gain insight into the cellular origins of this unique tubal pathway to high-grade serous cancer, we cloned and both immortalized and transformed Fallopian tube stem cells (FTSCs). We demonstrated that pedigrees of FTSCs were capable of multipotent differentiation and that the tumours derived from transformed FTSCs shared the histological and molecular features of HGSC. We also demonstrated that altered expression of some biomarkers seen in transformed FTSCs and HGSCs (stathmin, EZH2, CXCR4, CXCL12, and FOXM1) could be seen as well in immortalized cells and their in vivo counterparts SCOUTs and STINs. Thus, a whole-genome transcriptome analysis comparing FTSCs, immortalized FTSCs, and transformed FTSCs showed a clear molecular progression sequence that is recapitulated by the spectrum of accumulated perturbations characterizing the range of proliferations seen in vivo. Biomarkers unique to STIC relative to normal tubal epithelium provide a basis for novel detection approaches to early HGSC, but must be viewed critically given their potential expression in lesser proliferations. Perturbations shared by both immortalized and transformed FTSCs may provide unique early targets for prevention strategies. Central to these efforts has been the ability to clone and perpetuate multipotent FTSCs.

PAX2-null secretory cell outgrowths in the oviduct and their relationship to pelvic serous cancer.

With the exception of germ-line mutations in ovarian cancer susceptibility genes, genetic predictors for women destined for ovarian serous cancer cannot be identified in advance of malignancy. We recently showed that benign secretory cell outgrowths (SCOUTs) in the oviduct are increased in frequency with concurrent serous cancer and typically lack PAX2 expression (PAX2-null). The present study examined the relationship of PAX2-null SCOUTs to high-grade serous cancers by comparing oviducts from women with benign gynecologic conditions and high-grade serous cancers. PAX2-null SCOUTs were identified by immunostaining and computed as a function of location, frequency (F) per number of cross-sections examined, and age. Six hundred thirty-nine cross-sections from 35 serous cancers (364) and 35 controls (275) were examined. PAX2-null SCOUTs consisted of discrete linear stretches of altered epithelium ranging from cuboidal/columnar, to pseudostratified, the latter including ciliated differentiation. They were evenly distributed among proximal and fimbrial tubal sections. One hundred fourteen (F=0.31) and 45 (F=0.16) PAX2-null SCOUTs were identified in cases and controls, respectively. Mean individual case-specific frequencies for cases and controls were 0.39 and 0.14, respectively. SCOUT frequency increased significantly with age in both groups (P=0.01). However, when adjusted for age and the number of sections examined, the differences in frequency between cases and controls remained significant at P=0.006. This study supports a relationship between discrete PAX2 gene dysregulation in the oviduct and both increasing age and, more significantly, the presence of co-existing serous cancer. We propose a unique co-variable in benign oviductal epithelium-the PAX2-null SCOUT-that reflects underlying dysregulation in genes linked to serous neoplasia.