干细胞因子联合粒细胞集落刺激因子动员骨髓干细胞促进单侧输尿管梗阻大鼠肾脏损伤的修复

目的 研究干细胞因子（SCF）联合粒细胞集落刺激因子（G-CSF）动员单侧输尿管梗阻（UUO）大鼠骨髓干细胞对肾间质中微血管、纤维化程度和肾功能的影响,并探讨其对微血管影响的可能机制。 方法 128只大鼠按数字随机法分为假手术组（Sham组）、SCF联合G-CSF动员组（SCF-G组）、UUO组、UUO+SCF-G组。于实验第 5、14、21、28天每组各随机抽取8只处死,检测Scr、肾间质CD34阳性表达细胞数目和Ⅷ因子阳性表达细胞数目、肾间质纤维化和间质病理损害积分、肾皮质血管内皮生长因子（VEGF）mRNA和血小板反应蛋白1（TSP-1）mRNA的表达。 结果 (1)UUO组2周时可见到肾间质纤维化伴肾小管周微血管的丢失。（2）UUO+SCF-G组肾间质干细胞归巢数目明显高于UUO组和Sham组（P < 0.05）。（3）UUO+SCF-G组肾小管周微血管指数减少出现的时间晚于UUO组（P < 0.05）。（4）第14、21、28天UUO+SCF-G组间质化纤维程度和肾小管损伤程度均轻于UUO组（P < 0.05）。（5）UUO+SCF-G组术后VEGF mRNA表达下调出现的时间晚于UUO组,且表达均高于同期UUO组 （P < 0.05)。（6）UUO+SCF-G组术后TSP-1 mRNA表达增高出现的时间晚于UUO组,且表达均低于同期UUO组（P < 0.05）。（7）在UUO组和UUO+SCF-G组中,肾小管周微血管指数与Scr、间质纤维化积分和肾小管间质病理积分均呈负相关;肾皮质VEGF mRNA表达与肾小管周微血管指数呈正相关;肾皮质TSP-1 mRNA表达与肾小管周微血管指数呈负相关。 结论 （1）UUO大鼠存在肾小管周微血管丢失,并与肾间质纤维化及间质病理损伤相关。（2）联合应用SCF和G-CSF动员骨髓干细胞可以归巢至受损的肾脏,有助于减少肾小管周微血管丢失,并进而减轻肾间质纤维化和间质损害,保护肾功能。（3）联合应用SCF和G-CSF可以上调肾皮质VEGF mRNA水平和下调TSP-1 mRNA水平,这可能是其促进内皮细胞修复及保护肾间质微血管损伤的机制之一。     

动员自体骨髓干细胞对大鼠急性肾小管坏死的治疗

目的：观察粒细胞集落刺激因子联合干细胞因子动员骨髓干细胞的作用、骨髓干细胞是否具有向损伤肾组织归巢的能力及其在肾脏组织中的分布,初步探讨粒细胞集落刺激因子联合干细胞因子是否具有促进急性肾小管坏死修复的作用。方法：160只8～10周龄雄性SD大鼠随机分为4组：对照组,模型组、G-CSF＋SCF治疗组、G-CSF＋SCF对照组,检测：（1）外周血白细胞总数及单个核细胞中CD34＋细胞百分比的变化;（2）尿NAG酶检测;（3）肾脏组织病理学改变;（4）肾组织CD34＋细胞表达变化。结果：（1）G-CSF＋SCF治疗组和G-CSF＋SCF对照组外周血中白细胞数、CD34＋细胞百分比于第5天达高峰,与对照组、模型组相比,差异有统计学意义（P〈0.05）,以后逐渐下降;相应地,G-CSF＋SCF治疗组肾组织内CD34＋细胞较对照组、模型组也明显增多（P〈0.05）。（2）手术后第5、10、17天,G-CSF＋SCF治疗组尿NAG酶、肾脏病理学改变均明显好于模型组（P〈0.05）。第24天G-CSF＋SCF治疗组尿NAG酶、肾脏病理学改变基本恢复正常,而模型组仍异常。第31天各组间尿NAG酶、肾脏病理学改变其差异无统计学意义。结论：（1）粒细胞集落刺激因子和干细胞因子联合应用对缺血再灌注损伤诱发急性肾小管坏死大鼠的骨髓干细胞有显著的动员作用。（2）骨髓干细胞能在损伤的肾小管归巢和定居,并可能参与损伤肾组织的修复。（3）粒细胞集落刺激因子和干细胞因子联合应用能在一定程度上加速急性肾小管坏死后肾功能的修复。     

骨髓来源细胞移植对实验性肾小球肾炎小鼠的作用

目的：利用骨髓移植的方法观察骨髓来源细胞在小鼠实验性肾小球肾炎中的作用。方法：以绿色荧光蛋白（GFP）标记的C57BL／6转基因小鼠为供体,同种无标记小鼠为受体鼠,受体鼠在接受供体骨髓细胞前经亚致死剂量^60Co照射。并于移植5周后以尾静脉注射的方式接受竹叶青蛇毒注射;蛇毒注射后7、14、28、56d利用免疫组织化学和免疫荧光双重染色方法观察受体鼠肾脏内的GFP阳性细胞及受体鼠肾脏病理变化,其中一组受体鼠在蛇毒注射后接受连续1周的粒巨系一集落刺激因子（GM-CSF）腹腔注射,观察GM-CSF对骨髓来源细胞及受体鼠的影响。结果：无论有无蛇毒损伤,荧光显微镜下受体鼠肾脏内均未见明亮的绿色荧光。GFP免疫组织化学可见所有受体鼠的肾小管上皮内均有少量细胞质棕褐色、细胞核大且紫蓝的GFP阳性细胞,包括那些骨髓移植后无蛇毒损伤的受体鼠;肾小球内也可见上述细胞,但在无蛇毒损伤的受体鼠内肾小球内未见上述细胞;激光共聚焦显微镜未见到明显双染色阳性的细胞,从形态上证实肾小球内的这些GFP阳性细胞大多为血细胞。那些接受GM-CSF注射的受体鼠肾脏内,GFP阳性细胞没有明显增加,而且肾脏损伤恶化,表现为蛇毒注射后1周出现了明显的局灶性节段性肾小球硬化。结论：骨髓来源细胞在蛇毒诱导的系膜增生型肾小球肾炎小鼠肾脏内向肾小管和肾小球细胞均可少量转化,但由于转化率低及肾小球结构的复杂性,向肾小球细胞的转化更加不易被识别;GM-CSF注射未能增加外源性骨髓细胞向肾脏实质细胞的转化而使受体鼠肾脏损伤恶化,于病程早期出现了局灶性节段性肾小球硬化。     

绿色荧光蛋白转基因小鼠脂肪干细胞治疗后肢缺血的实验研究

目的观察绿色荧光蛋白(GFP)转基因小鼠来源的脂肪干细胞(ADSCs)治疗小鼠后肢缺血的效果及其自身所带荧光标记的有效性。方法取4周龄GFP转基因小鼠的脂肪组织,消化获取GFP来源的脂肪干细胞(GFP-ADSCs),并用流式鉴定其表面的干细胞抗原。建立C57BL/6小鼠左后肢缺血模型并随机分成两组(每组16只):一组后肢缺血的肌肉组织内注射P3代的GFPADSCs 1×106个/100μl,对照组于同样部位注射100μl PBS。1个月后利用苏木素-伊红(HE)、免疫组织化学(IHC)及免疫荧光(IF)染色行CD31染色观察缺血肌肉组织内血管新生情况。结果1从GFP转基因小鼠的脂肪组织中可以获得大量GFP-ADSCs并表达干细胞表面抗原CD90及CD105;2 GFP-ADSCs被成功地诱导成脂成骨;3 GFP-ADSCs组总残肢恢复率显著高于PBS组(P0.05);4 1个月后GFP-ADSCs治疗组缺血的肌肉组织内IHC染色CD31可见较多的新生血管,其微血管密度数显著高于PBS组(P0.05);IF染色显示GFP-ADSCs治疗组的新生血管表达内皮细胞的特异性标记CD31和GFP,而PBS组则未见GFP绿色荧光表达。结论从GFP转基因小鼠的脂肪组织中可以获取大量的ADSCs,其能够促进小鼠后肢缺血肌肉组织内的血管新生,自带的GFP可以示踪ADSCs在受体内的存活、迁移及分化。     

骨髓干细胞参与小鼠急性肾小管坏死修复的实验研究

【摘要】 目的 观察在生理和病理情况下,骨髓来源的干细胞(BMSC)能否分化成肾小管上皮细胞。 方法 绿色荧光蛋白(GFP)标记的C57BL/6转基因小鼠提供骨髓细胞。同种无荧光标记的C57BL/6小鼠100只分为正常对照组、全身照射组、缺血再灌注组、骨髓移植组、骨髓移植+缺血再灌注组。受体鼠的骨髓重建经血液常规检查和流式细胞仪检测确认,并采用荧光组织化学、免疫组织化学等方法观察绿色荧光标记的BMSC在受体鼠肾脏的分布及数量。 结果 全身致死剂量γ射线照射未造成小鼠肾脏组织结构和生理功能的明显改变。骨髓移植后第56、84天的受体鼠肾小管中有少量GFP阳性细胞的存在[(78.75±5.99)%、(79.58±4.60)%],激光共聚焦显微镜进一步证实这些细胞位于肾小管,并表达肾小管上皮细胞特异性的功能蛋白megalin。 结论 在生理和病理情况下,骨髓干细胞均可以向肾小管上皮细胞转分化,参与肾小管上皮细胞的更新,并且在急性肾小管坏死的病理条件下,骨髓干细胞的肾向转化率与肾脏受损程度有关。     

粒细胞集落刺激因子和干细胞因子对骨髓单个核细胞的动员效率及其机制

目的 联合应用粒细胞集落刺激因子(G-CSF)和干细胞因子(SCF)动员骨髓单个核细胞,评价其动员效果,探讨CXCL12/CXCR4信号通路在骨髓单个核细胞动员中的作用及机制.方法 将昆明小鼠随机分为两组,治疗组皮下注射重组鼠G-CSF 100μg/(kg·d)和重组鼠SCF25μg/(kg·d),连续使用5d;对照组皮下注射等剂量的生理盐水.每组于不同时间点取小鼠骨髓,分离培养骨髓单个核细胞,计数成纤维样细胞集落形成单位(CFU-F)的个数;应用流式细胞仪分选CD34+ CXCR4+单个核细胞(MNCs);应用酶联免疫吸附试验(ELISA)法测定骨髓细胞外液CXCL12a的水平;采用逆转录-聚合酶链反应(RT-PCR)检测骨髓CXCL12 mRNA表达变化.结果 应用G-CSF/SCF后,骨髓及外周血中单个核细胞计数较对照组明显增加(P<0.01),CFU-F形成能力显著增强(P<0.05);流式分选表明CD34+ CXCR4+细胞占骨髓CD34+单个核细胞总数的(44.6±8.7)%;RT-PCR和EUSA检测示骨髓CXCL12 mRNA表达下降,骨髓细胞外液CXCL12蛋白也显著下降,两者变化一致.结论 G-CSF/SCF可有效地诱导骨髓单个核细胞动员,其机制可能是通过破坏骨髓CXCL12/CXCR4信号通路平衡,下调CXCL12/CXCR4间相互作用,以促进骨髓单个核细胞动员.     

骨髓来源细胞移植对糖尿病小鼠胰岛功能的影响

目的 观察骨髓来源细胞(BMDCs)移植对糖尿病小鼠胰岛功能的影响.方法 建立糖尿病小鼠模型并分成两组:实验组小鼠(n=8)通过尾静脉移植BMDCs;对照组小鼠(n=8)通过尾静脉注射磷酸盐缓冲液(PBS).观察两组小鼠血糖的变化、胰岛数量、胰腺组织形态学特征及相关标记物的表达.结果 与对照组比较,实验组小鼠移植后第4周血糖出现明显下降(20.7±5.2)比(27.1±1.4)mmol/L,P＜0.05,并持续下降至第6周(16.9±6.0)比(27.7±0.3)mmol/L,P＜0.01,胰岛数目显著增加(22.9±4.8)比(11.6±5.2)个,P＜0.01;实验组小鼠胰岛周围和胰岛内发现绿色荧光蛋白(GFP)阳性细胞,部分GFP阳性细胞同时表达CD34,但未发现同时表达GFP和insulin的细胞.结论 BMDCs移植能促进糖尿病小鼠胰岛的修复和再生,但BMDCs在糖尿病小鼠体内不能转分化为胰岛β细胞,CD34阳性细胞在损伤胰岛修复和再生的过程中起重要作用.     

粒细胞集落刺激因子减轻小鼠混合骨髓移植后移植物抗宿主病的实验研究

目的探讨同基因骨髓混合一定比例粒细胞集落刺激因子(G-CSF)动员的异基因骨髓移植能否减轻急性移植物抗宿主病(aGVHD).方法将BALB/c与BCF1(BALB/c×C57BL/6)小鼠或与G-CSF动员BCF1小鼠脾细胞按一定比例混合,腹腔注入BALB/c幼鼠,制备新生小鼠GVHD模型,结果以脾指数表示.成年雌性BALB/c小鼠接受60Co全身照射8.5Gy后进行移植,移植物为BALB/c与雄性BCF1或与G-CSF动员BCF.小鼠骨髓细胞按一定比例的混合,移植细胞总数60×105个/只.观察移植小鼠aGVHD典型症状、病理表现及存活率.ELISA法测定细胞因子含量,流式细胞术分析T细胞亚群变化.结果(1)注射BALB/c与BCF1小鼠脾细胞混合比例为21、11及异基因BCF1小鼠脾细胞的新生小鼠均发生GVHD;但G-CSF动员与否,GVHD发生程度差异有统计学意义.(2)21及11混合骨髓移植(MBMT)组小鼠有中到重度GVHD表现;经G-CSF动员的MBMT组小鼠8周存活率较未动员组明显提高(P＜0.05).(3)G-CSF动员供鼠后L3T4+细胞下降显著,L3T4+/Lyt2+比值明显低于未动员组(P＜0.01).(4)G-CSF动员供鼠后混合淋巴细胞反应(MLR)细胞培养上清中,IL-2、IFN-γ水平降低,IL-4水平升高.结论同基因骨髓混合一定量H-2半相合异基因骨髓移植可减轻GVHD的发生;G-CSF动员供鼠可进一步减轻MBMT后GVHD的发生.其机理可能与IL-2、IFN-γ下降、IL-4升高有关.     

咪达唑仑和异丙酚对急性心肌梗死大鼠血清VEGF浓度及G-CSF药物动员骨髓干细胞效果的影响

目的 评价咪达唑仑和异丙酚对急性心肌梗死大鼠血清血管内皮生长因子(VEGF)浓度及粒细胞集落刺激因子(G-CSF)药物动员骨髓干细胞效果的影响.方法 雄性Wistar大鼠36只,体重250 ～ 280 g,采用结扎左冠状动脉前降支的方法制备急性心肌梗死模型,采用腹腔连续注射G-CSF 5d进行药物动员,于药物动员后第7天,按照随机数字表法,将大鼠随机分为G-CSF组(G组)、咪达唑仑组(M组)及异丙酚组(P组),每组12只.G组以0.5 ml/h的速率股静脉输注生理盐水6h;M组股静脉输注咪达唑仑0.05 mg·kg-·h-1 6 h;P组股静脉输注异丙酚5mg·kg-1 ·h-16 h.于给药完毕后经股静脉取血,采用流式细胞仅测定CD34+单核细胞( CD34+ MNC)和内皮祖细胞(EPCs)数目,采用ELISA法测定血清VEGF浓度.于心肌梗死后4周每组随机取6只大鼠测定左心室舒张末压(LVEDP)、最大收缩速率(+dp/dtmax)和最大舒张速率(- dp/max).结果 与G组比较,M组CD34+MNC及EPCs细胞数目增加,血清VEGF浓度升高,LVEDP下降,-dp/dtmax的绝对值升高(P＜0.05),P组LVEDP下降,- dp/dtmax的绝对值升高(P＜0.05);与P组比较,M组CD34+MNC及EPCs细胞数目增加,血清VEGF浓度升高,LVEDP下降,- dp/dtmax的绝对值升高(P＜0.05).结论 咪达唑仑可促进VEGF的释放,加强G-CSF动员骨髓干细胞的作用,改善急性心肌梗死后大鼠的心脏功能;异丙酚不能促进VEGF的释放及无骨髓干细胞动员的作用.     

VLA-4单克隆抗体那他珠单抗(Natalizumab)动员人CD34+造血干细胞的临床研究

VLA-4是表达于造血细胞表面的β-1整合素家族的α-4亚单位,是与CD34+细胞动员和迁移有关的黏附分子.骨髓来源的CD34+细胞VLA-4表达量显著高于外周血CD34+细胞,提示VLA-4的表达与造血干细胞动员到外周血有密切的关系.VLA-4单克隆抗体那他珠单抗(Natalizumab)被用于治疗自身免疫性疾病,如多发性硬化、Crohn病等,本研究旨在探讨Natalizumab在动员CD34+造血干细胞中的作用.     

Enhanced mobilization of bone marrow cells does not ameliorate renal fibrosis.

BACKGROUND: The plasticity of bone marrow-derived stem cells, also comprising haematopoietic stem cells, has been shown to extend to renal epithelial lineages. Yet, the low rate of their contribution to the injured kidney has led to questions regarding their significance in tissue repair after acute injury. We describe here the effect of stem cell mobilization therapy on the progression of renal fibrosis in a mouse model of chronic obstructive nephropathy. METHODS: Mice were subjected to unilateral ureter obstruction (UUO) and treated with stem cell factor (SCF) and granulocyte-colony stimulating factor (G-CSF) or saline. Circulating cells were analysed by flow cytometry; labelled bone marrow c-KIT(HIGH) cells were injected into animals subjected to UUO. Granulocytes, macrophages, cellular proliferation or apoptosis and myofibroblasts were detected by immunostaining. Collagen deposition was determined by measuring renal hydroxyproline contents. Cytokine levels were measured by ELISA. RESULTS: SCF/G-CSF treatment of mice induced significant haematopoietic stem and progenitor cell mobilization from the bone marrow. Although these cells are able to migrate to the obstructed kidney, they did not influence renal damage, fibrosis and inflammatory cell influx. CONCLUSIONS: Although SCF/G-CSF treatment significantly enhanced the availability of haematopoietic stem cells to the obstructed kidney, the progression of renal fibrosis could not be delayed or halted. Our results indicate that effective stem cell mobilization does not alter renal fibrosis.     

Evaluation of the ability of bone marrow derived cells to engraft the kidney and promote renal tubular regeneration in mice following exposure to cisplatin

It has been suggested that bone marrow derived stem cells have the ability to engraft the kidney and improve the outcome of severe acute kidney injury (AKI) in mice exposed to high doses of cisplatin, providing hope for cancer patients in whom irreversible renal damage occasionally occurs following the use of this highly effective anti-tumor drug. We tested the therapeutic potential of bone marrow derived cells injected during the acute phase (day 3 after cisplatin administration) of experimentally-induced AKI in C57Bl6/J mice, characterized by massive tubular necrosis, apoptosis, and a low proliferation capacity. We failed to show any benefit of bone marrow derived cells versus a regular homogenate of intact renal cells, or normal saline. Using cell tracers and flow cytometry, we demonstrated that bone marrow derived cells did indeed home to the bone marrow of the recipients but failed to settle in the kidney. Conversely, renal cells homed to injured kidneys. However, neither cell therapy protected the animals against cisplatin-induced death. We therefore question the short-term efficacy of bone marrow derived cells used to repair established injuries of the tubular epithelium.     

Granulocyte colony-stimulating factor and an RARalpha specific agonist, VTP195183, synergize to enhance the mobilization of hematopoietic progenitor cells

BACKGROUND: Failure to mobilize adequate numbers of hematopoietic stem and progenitor cells (HSPC) is an important clinical problem. Since bone marrow (BM) neutrophils play a central role in HSPC mobilization, we hypothesized that granulocyte colony-stimulating factor (G-CSF)-mediated mobilization would be enhanced by further expanding the size of the BM granulocyte pool. METHODS: We tested the potential of the retinoic acid receptor alpha (RARalpha) specific agonist VTP195183, and the pan-RAR agonist all-trans retinoic acid (ATRA), to enhance G-CSF-mediated mobilization of HSPC, in two mouse strains. RESULTS: Pretreatment of mice with VTP195183 significantly increased the number of leukocytes, colony-forming cells, and early engrafting hematopoietic stem cells (HSC) mobilized in the blood in response to G-CSF. In contrast, ATRA had only a marginal effect on G-CSF-induced mobilization. HSPC mobilization synergy between VTP195183 and G-CSF occurred only when mice were preconditioned with VTP195183 prior to G-CSF. This preconditioning was shown to increase the numbers of granulocyte/macrophage progenitors in the BM. Treatment with VTP195183 and G-CSF was accompanied by enhanced levels of active neutrophil proteases in the BM extracellular fluid compared to G-CSF treatment alone. CONCLUSIONS: VTP195183 treatment increases the numbers of immature granulocyte progenitors in BM and subsequently synergizes to enhance G-CSF-mediated mobilization of HSPC. These data demonstrate a novel approach to improve G-CSF-induced mobilization by accelerating granulocyte maturation in the BM. These findings are currently being tested in a clinical trial of VTP195183 plus G-CSF for mobilization of HSPC in human patients.     

Mesenchymal, but not hematopoietic, stem cells can be mobilized and differentiate into cardiomyocytes after myocardial infarction in mice

Bone marrow (BM) cells are reported to contribute to the process of regeneration following myocardial infarction. The present study examined two independent clonal studies to determine the origin of bone marrow (BM)-derived cardiomyocytes. First, we transplanted single CD34(-)c-kit(+)Sca-1(+)lineage(-) side population cells (hematopoietic stem cells) from enhanced green fluorescent protein (EGFP)-transgenic mice into lethally irradiated mice, induced myocardial infarction, and treated them with G-CSF to mobilize stem cells. At 8 weeks, we could not find any EGFP(+) cardiomyocytes. In contrast, more than 5000 EGFP(+) cardiomyocytes were observed in whole BM cell-transplanted mice, suggesting that they were derived from non-hematopoietic cells. Next, clonally purified mesenchymal stem cells (MSC) that expressed EGFP in the cardiomyocyte-specific manner were transplanted directly into BM of lethally irradiated mice, and similar experiment was performed. EGFP(+) actinin(+) cells were observed in the ischemic myocardium, indicating that MSC had been mobilized and differentiated into cardiomyocytes. Together, these results suggest that the origin of the BM-derived cardiomyocytes is MSC.     

The regenerative potential of stem cells in acute renal failure

Adult stem cells have been characterized in several tissues as a subpopulation of cells able to maintain. generate, and replace terminally differentiated cells in response to physiological cell turnover or tissue injury. Little is known regarding the presence of stem cells in the adult kidney but it is documented that under certain conditions, such as the recovery from acute injury, the kidney can regenerate itself by increasing the proliferation of some resident cells. The origin of these cells is largely undefined; they are often considered to derive from resident renal stem or progenitor cells. Whether these immature cells are a subpopulation preserved from the early stage of nephrogenesis is still a matter of investigation and represents an attractive possibility. Moreover, the contribution of bone marrow-derived stem cells to renal cell turnover and regeneration has been suggested. In mice and humans, there is evidence that extrarenal cells of bone marrow origin take part in tubular epithelium regeneration. Injury to a target organ can be sensed by bone marrow stem cells that migrate to the site of damage, undergo differentiation, and promote structural and functional repair. Recent studies have demonstrated that hematopoietic stem cells were mobilized following ischemia/reperfusion and engrafted the kidney to differentiate into tubular epithelium in the areas of damage. The evidence that mesenchymal stem cells, by virtue of their renoprotective property, restore renal tubular structure and also ameliorate renal function during experimental acute renal failure provides opportunities for therapeutic intervention.     

Proliferation of bone marrow-derived cells contributes to regeneration after folic acid-induced acute tubular injury

Studies of tissue from recipients of bone marrow transplantation or organ allograft suggest that bone marrow-derived cells (BMDC) may differentiate into a variety of nonhematologic tissues, including renal tubular epithelium. The aims of this study were to examine whether BMDC contribute to recovery after acute renal injury and to assess the effects of cytokine mobilization on regeneration. Female mice (6 wk old) were lethally irradiated and transplanted with male bone marrow (BM) cells and later assigned into control, folic acid-treatment, and folic acid-treatment with granulocyte-colony stimulating factor (G-CSF), and control with G-CSF. Tritiated thymidine was given 1 h before death. Kidney sections were stained for a tubular epithelial marker, Y chromosome (in situ hybridization), periodic acid-Schiff staining, and subjected to autoradiography. Renal tubular epithelial cells in S-phase were scored as female (indigenous) or male (BM-derived). This is the first report to show that BMDC can respond by engrafting the renal tubules and undergo DNA synthesis after acute renal injury. BMDC contributed to the renal tubular epithelial cell population, although most (90%) renal tubular regeneration came from female indigenous cells. Some evidence was found for cell fusion between indigenous renal tubular cells and BMDC, but this was infrequent and the significance and consequences of cell fusion in the kidney are unresolved. G-CSF treatment nearly doubled the frequency of thymidine-labeled BM-derived tubular cells and might facilitate the recovery of renal tubular epithelium.     

Stem cells and progenitor cells in renal disease

Stem cells and progenitor cells are necessary for repair and regeneration of injured renal tissue. Infiltrating or resident stem cells can contribute to the replacement of lost or damaged tissue. However, the regulation of circulating progenitor cells is not well understood. We have analyzed the effects of erythropoietin on circulating progenitor cells and found that low levels of erythropoietin induce mobilization and differentiation of endothelial progenitor cells. In an animal model of 5/6 nephrectomy we could demonstrate that erythropoietin ameliorates tissue injury. Full regeneration of renal tissue demands the existence of stem cells and an adequate local "milieu," a so-called stem cell niche. We have previously described a stem cell niche in the kidneys of the dogfish, Squalus acanthus. Further analysis revealed that in the regenerating zone of the shark kidney, stem cells exist that can be induced by loss of renal tissue to form new glomeruli. Such animal models improve our understanding of stem cell behavior in the kidney and may eventually contribute to novel therapies.