Fate plasticity in the intestine: The devil is in the detail

The intestinal epithelium possesses a remarkable ability for both proliferation and regeneration.The last two decades have generated major advances in our understanding of the stem cell populations responsible for its maintenance during homeostasis and more recently the events that occur during injury induced regeneration.These fundamental discoveries have capitalised on the use of transgenic mouse models and in vivo lineage tracing to make their conclusions.It is evident that maintenance is driven by rapidly proliferating crypt base stem cells,but complexities associated with the technicality of mouse modelling have led to several overlapping populations being held responsible for the same behaviour.Similarly,it has been shown that essentially any population in the intestinal crypt can revert to a stem cell state given the correct stimulus during epithelial regeneration.Whilst these observations are profound it is uncertain how relevant they are to human intestinal homeostasis and pathology.Here,these recent studies are presented,in context with technical considerations of the models used,to argue that their conclusions may indeed not be applicable in understanding“homeostatic regeneration”and experimental suggestions presented for validating their results in human tissue.     

Heterogeneity in secretory responses of rat liver macrophages of different size

Abstract: Four subpopulations of hepatic macrophages, differing in size, were isolated from rat liver. The secretion of nitric oxide (NO), tumor necrosis factor-α (TNF-α), prostaglandin E (PGE) and interleukin-1 (IL-1) by freshly isolated as well as cultured cells was studied after in vitro stimulation with the immunomodulator muramyl dipeptide (MDP) in free or liposome-encapsulated form. Freshly isolated liver macrophages could be induced to secrete significant levels of NO, TNF-α, PGE and IL-1. The extent of secretion, however, varied substantially between macrophages of different size. The highest levels of secretion of TNF-α, PGE and IL-1 were observed in the fraction containing the large-size macrophages, while progressively lower levels of secretion were observed with decreasing size. In constrast, the highest levels of NO secretion were observed by small macrophages and steadily decreased with increasing size. Hepatic macrophages of different size displayed differences in secretory potential during in vitro culture. The ability of small liver macrophages to secrete NO, TNF-α, or PGE, following activation with MDP, gradually increased with time in culture. In contrast, large liver macrophages gradually lost their secretory ability after 1–2 days and the intermedicate-size cells after 2–3 days in culture. This functional heterogeneity in secretory properties among rat liver macrophages of different size is discussed with reference to their potential role and significance in host defense against metastatic tumor growth in the liver.     

Stem cells in gastric cancer

Gastric cancer(GC) is one of the leading causes of cancerrelated mortality worldwide.Cancer stem cells(CSCs),which were first identified in acute myeloid leukemia and subsequently in a large array of solid tumors,play important roles in cancer initiation,dissemination and recurrence.CSCs are often transformed tissue-specific stem cells or de-differentiated transit amplifying progenitor cells.Several populations of multipotent gastric stem cells(GSCs) that reside in the stomach have been determined to regulate physiological tissue renewal and injury repair.These populations include the Villin+ and Lgr5+ GSCs in the antrum,the Troy+ chief cells in the corpus,and the Sox2+ GSCs that are found in both the antrum and the corpus.The disruption of tumor suppressors in Villin+ or Lgr5+ GSCs leads to GC in mouse models.In addition to residing GSCs,bone marrow-derived cells can initiate GC in a mouse model of chronic Helicobacter infection.Furthermore,expression of the cell surface markers CD133 or CD44 defines gastric CSCs in mouse models and in human primary GC tissues and cell lines.Targeted elimination of CSCs effectively reduces tumor size and grade in mouse models.In summary,the recent identification of normal GSCs and gastric CSCs has greatly improved our understanding of the molecular and cellular etiology of GC and will aid in the development of effective therapies to treat patients.     

Crypt region localization of intestinal stem cells in adults

The intestinal epithelial lining plays a central role in the digestion and absorption of nutrients,but exists in a harsh luminal environment that necessitates continual renewal.This renewal process involves epithelial cell proliferation in the crypt base and later cell migration from the crypt base to the luminal surface.This process is dependent on multi-potent progenitor cells,or stem cells,located in each crypt.There are about 4 to 6 stem cells per crypt,and these stem cells are believed to generate distinct end-differentiated epithelial cell types,including absorptive cells,goblet cells,enteroendocrine cells and Paneth cells,while also maintaining their own progenitor cell state.Earlier studies suggested that intestinal stem cells were located either in the crypt base interspersed between the Paneth cells [i.e.crypt base columnar（CBC） cell model] or at an average position of 4 cells from the crypt base [i.e.label-retaining cells（LRC ＋4） model].Recent studies have employed biomarkers in the in vivo mammalian state to more precisely evaluate the location of these progenitor cells in the intestinal crypt.Most notable of these novel markers are Lgr5,a gene that encodes a G-protein-coupled receptor with expression restricted to CBC cells,and Bmi 1,which encodes a chromatin remodeling protein expressed by LRC.These studies raise the possibility that there may be separate stem cell lines or different states of stem cell activation involved in the renewal of normal mammalian intestinal tract.     

hPepT1 transports muramyl dipeptide, activating NF-kappaB and stimulating IL-8 secretion in human colonic Caco2/bbe cells

BACKGROUND AND AIMS: Bacterial proteoglycan-derived muramyl dipeptide (MDP) activates the intracellular NOD2/CARD15 gene product. How intestinal epithelial cells take up MDP is poorly understood. We hypothesized that the intestinal apical di-/tripeptide transporter, hPepT1, transports MDP, thereby activating downstream pathways similar to nuclear factor kappa B (NF-kappaB). METHODS: Time- and concentration-dependent (3)H-MDP uptakes were studied in Caco2/bbe (C2) cell monolayers where hPepT1 expression was either over- or underexpressed, using an inducible adenovirus system or silencing RNA (siRNA), respectively. NF-kappaB activation and interleukin (IL)-8 and monocyte chemoattractant protein-1 (MCP-1) release were determined by enzyme-linked immunosorbent assay. NOD2/CARD15 expression was inhibited by siRNA. MDP in human duodenal, cecal, and stool samples was measured. RESULTS: MDP, but not its isoforms, inhibited uptake of glycosylsarcosine in C2 cells, indicating stereoselective and competitive inhibition. Approximately 90% of the MDP was cytosolic, showing uptake rather than binding. The K m for MDP uptake was 4.3 mmol/L. Cells overexpressing hPepT1 showed increased Gly-Sar and MDP uptake, whereas decreased uptake was observed after hPepT1 siRNA-inhibition. MDP treatment activated NF-kappaB, resulting in IL-8 release, an effect blocked by siRNA-inhibited expression of NOD2/CARD15. MDP content in cecal and stool samples (in normal subjects) was 20-87 micromol/L, but undetectable in duodenal fluid. CONCLUSIONS: In colonic epithelial cells, MDP is taken up by hPepT1 and activates NF-kappaB and chemokine production. Because hPepT1 expression in chronic colonic inflammation is increased, this may play an important role in promoting colonocyte participation in host defense and pathogen clearance through increased uptake of MDP.     

Glioma stem cells: turpis omen in nomen? (the evil in the name?)

High‐grade gliomas remain incurable and lethal. Through the availability of the stem‐like cells responsible for glioblastoma (GB) formation, expansion, resilience and recurrence, the discovery of glioma cancer stem cells (GCSCs) is revolutionizing this field. GCSCs provide an unprecedented opportunity to reproduce and study GB pathophysiology more accurately. This critically emphasizes our ability to unambiguously identify, isolate and investigate cells that do qualify as GCSCs, to use them as a potential model that is truly predictive of GBs and of their regulation and response to therapeutic agents. We review this concept against the background of key findings on somatic, neural and solid tumour stem cells (SCs), also taking into account the emerging phenomenon of phenotypic SC plasticity. We suggest that basic approaches in these areas can be imported into the GCSC field, so that the same functional method used to identify normal somatic SCs becomes the most appropriate to define GCSCs. This, combined with knowledge of the cellular and molecular basis of normal adult neurogenesis, promises to improve the identification of GCSCs and of selective markers, as well as the development of innovative, more specific and efficacious antiglioma strategies.     

干细胞治疗基础与临床——国内外最新动态

近年来,干细胞治疗作为一项治疗人类多种疾病的崭新技术,相关的基础研究与临床试验呈现出快速增长的趋势,该文对胚胎干细胞,成体干细胞及诱导性多能干细胞当前的进展情况进行了综述,干细胞临床治疗拥有广阔的发展前景。     

5-氟尿嘧啶作用人肝癌细胞系SMMC-7721后残存细胞中肿瘤干细胞比例增加

目的主要探讨5-氟尿嘧啶(5-FU)作用肝癌细胞系SMMC-7721后残余细胞中NCAM/CD56、ICAM-1/CD54、EpCAM、CD133及ABCG2阳性细胞表达率的变化。方法检测不同浓度5-FU作用于SMMC-7721细胞系前后细胞增殖能力的变化,流式细胞仪检测残存细胞的细胞周期分布以及5种表面标志物阳性细胞表达率的变化。结果不同浓度5-FU均可抑制SMMC-7721增殖。使用10μg/mL的5-FU浓度作用48 h进一步研究,SMMC-7721细胞周期各期细胞比例均较对照组有影响,且G0/G1、S和G2/M期5-FU作用前后差异有统计学意义(P<0.05),G0/G1期阻滞明显。5-FU处理使SMMC-7721 5种细胞表面标志物阳性细胞比例均明显升高,差异均具有统计学意义(P<0.05),阳性细胞比例均明显升高。结论上述实验提示肝癌干细胞逃避5-FU单药物的杀伤可能是临床上肝癌化疗失败和肿瘤复发的重要原因,同时,此实验方法可以作为肝癌干细胞富集的科研模型。