Vascularized and functional human liver from an iPSC-derived organ bud transplant.

A critical shortage of donor organs for treating end-stage organ failure highlights the urgent need for generating organs from human induced pluripotent stem cells (iPSCs). Despite many reports describing functional cell differentiation, no studies have succeeded in generating a three-dimensional vascularized organ such as liver. Here we show the generation of vascularized and functional human liver from human iPSCs by transplantation of liver buds created in vitro (iPSC-LBs). Specified hepatic cells (immature endodermal cells destined to track the hepatic cell fate) self-organized into three-dimensional iPSC-LBs by recapitulating organogenetic interactions between endothelial and mesenchymal cells. Immunostaining and gene-expression analyses revealed a resemblance between in vitro grown iPSC-LBs and in vivo liver buds. Human vasculatures in iPSC-LB transplants became functional by connecting to the host vessels within 48 hours. The formation of functional vasculatures stimulated the maturation of iPSC-LBs into tissue resembling the adult liver. Highly metabolic iPSC-derived tissue performed liver-specific functions such as protein production and human-specific drug metabolism without recipient liver replacement. Furthermore, mesenteric transplantation of iPSC-LBs rescued the drug-induced lethal liver failure model. To our knowledge, this is the first report demonstrating the generation of a functional human organ from pluripotent stem cells. Although efforts must ensue to translate these techniques to treatments for patients, this proof-of-concept demonstration of organ-bud transplantation provides a promising new approach to study regenerative medicine.

Aorta-derived mesoangioblasts can be differentiated into functional uterine epithelium, but not prostatic epithelium or epidermis, by instructive mesenchymes.

Mesoangiobasts are blood vessel-derived stem cells that differentiate into smooth, skeletal, and cardiac muscle cells. We have reported that postnatal aorta-derived mesoangioblasts (ADM) regenerate skeletal muscle and prevent onset of dilated cardiomyopathy in animal models of Duchenne muscular dystrophy. ADM also differentiate into myelinating glial cells, suggesting they are multipotent and capable of generating mesodermal or ectodermal derivatives. Mesenchyme of some fetal organs is a potent instructive inducer. Here we examined whether ADM can differentiate into prostatic, uterine, and skin epithelium by recombining ADM with fetal or neonatal mesenchyme from these organs and grafting them under the renal capsule of syngeneic hosts. In tissue recombinants of uterine mesenchyme (UtM) and ADM, ADM formed histologically normal simple columnar uterine epithelium that expressed estrogen receptor 1 and in response to estrogen showed increased mitogenesis and downregulation of progesterone receptor. In contrast, ADM did not differentiate into prostatic epithelium or epidermis when recombined with urogenital sinus mesenchyme or fetal dermis, respectively. These results indicate that ADM can respond to cues from neonatal UtM and differentiate into morphologically and functionally normal uterine epithelial cells, and support previous reports that ADM can differentiate into a variety of tissues of the mesodermal lineage. However, these data indicate that ADM are restricted in their capacity to differentiate into endodermal and ectodermal derivatives such as prostatic and skin epithelial cells, respectively.

Brief report: a bioassay to identify primary human prostate cancer repopulating cells.

Cancer cells are heterogeneous in both their phenotypes and ability to promote tumor growth and spread. Xenografting is used to identify the most highly capable cells of regenerating tumors, referred to as cancer repopulating cells. Because prostate cancers (PCa's) rarely grow as xenografts, indentifying PCa repopulating cells has not been possible. Here, we report improved methods to xenograft localized primary PCa tissues using chimeric grafts with neonatal mouse mesenchyme. Xenograft survival of tumor tissue was significantly increased by neonatal mesenchyme (six of six patients, 66% of grafts, versus four of six patients, 41% of grafts) and doubled the proliferation index of xenografted cancer cells. When applied to isolated PCa cells, neonatal mesenchyme effectively reconstituted PCa's and increased xenograft survival (four of nine patients; 32% of grafts with mesenchyme and 0% without), and supported active cancer cell proliferation. Using this assay, we showed that unfractionated α2ß1integrin(hi) and α2ß1integrin(lo) cells from primary localized PCa's demonstrated tumor formation at comparable rates, similar to previous reports using metastatic specimens. Thus, this new protocol efficiently established tumors and enabled proliferative expansion of both intact tumor tissue and fractionated cancer cells, providing a bioassay to identify and therapeutically target PCa repopulating cells.

Distinct contributions from the hindbrain and mesenchyme to inner ear morphogenesis.

A mature inner ear is a complex structure consisting of vestibular and auditory components. Microsurgical ablations, rotations, and translocations were performed in ovo to identify the tissues that control inner ear morphogenesis. We show that mesenchyme/ectoderm adjacent to the developing ear specifically governs the shape of vestibular components - the semicircular canals and ampullae - by conferring anteroposterior axial information to these structures. In contrast, removal of individual hindbrain rhombomeres adjacent to the developing ear preferentially affects the growth and morphogenesis of the auditory subdivision, the cochlear duct, or basilar papilla. Removal of rhombomere 5 affects cochlear duct growth, while rhombomere 6 removal affects cochlear growth and morphogenesis. Rotating rhombomeres 5 and 6 along the anteroposterior axis also impacts cochlear duct morphogenesis but has little effect on the vestibular components. Our studies indicate that discrete tissues, acting at a distance, control the morphogenesis of distinct elements of the inner ear. These results provide a basis for identifying factors that are essential to vestibular and auditory development in vertebrates.

Valproic acid stimulates myogenesis in pluripotent stem cell-derived mesodermal progenitors in a NOTCH-dependent manner.

Muscular dystrophies are debilitating neuromuscular disorders for which no cure exists. As this disorder affects both cardiac and skeletal muscle, patients would benefit from a cellular therapy that can simultaneously regenerate both tissues. The current protocol to derive bipotent mesodermal progenitors which can differentiate into cardiac and skeletal muscle relies on the spontaneous formation of embryoid bodies, thereby hampering further clinical translation. Additionally, as skeletal muscle is the largest organ in the human body, a high myogenic potential is necessary for successful regeneration. Here, we have optimized a protocol to generate chemically defined human induced pluripotent stem cell-derived mesodermal progenitors (cdMiPs). We demonstrate that these cells contribute to myotube formation and differentiate into cardiomyocytes, both in vitro and in vivo. Furthermore, the addition of valproic acid, a clinically approved small molecule, increases the potential of the cdMiPs to contribute to myotube formation that can be prevented by NOTCH signaling inhibitors. Moreover, valproic acid pre-treated cdMiPs injected in dystrophic muscles increase physical strength and ameliorate the functional performances of transplanted mice. Taken together, these results constitute a novel approach to generate mesodermal progenitors with enhanced myogenic potential using clinically approved reagents.

Developmental origins of species-specific muscle pattern.

Vertebrate jaw muscle anatomy is conspicuously diverse but developmental processes that generate such variation remain relatively obscure. To identify mechanisms that produce species-specific jaw muscle pattern we conducted transplant experiments using Japanese quail and White Pekin duck, which exhibit considerably different jaw morphologies in association with their particular modes of feeding. Previous work indicates that cranial muscle formation requires interactions with adjacent skeletal and muscular connective tissues, which arise from neural crest mesenchyme. We transplanted neural crest mesenchyme from quail to duck embryos, to test if quail donor-derived skeletal and muscular connective tissues could confer species-specific identity to duck host jaw muscles. Our results show that duck host jaw muscles acquire quail-like shape and attachment sites due to the presence of quail donor neural crest-derived skeletal and muscular connective tissues. Further, we find that these species-specific transformations are preceded by spatiotemporal changes in expression of genes within skeletal and muscular connective tissues including Sox9, Runx2, Scx, and Tcf4, but not by alterations to histogenic or molecular programs underlying muscle differentiation or specification. Thus, neural crest mesenchyme plays an essential role in generating species-specific jaw muscle pattern and in promoting structural and functional integration of the musculoskeletal system during evolution.

Insulin expressed from endogenously active glucose-responsive EGR1 promoter in bone marrow mesenchymal stromal cells as diabetes therapy.

Advances in islet transplantation have encouraged efforts to create alternative insulin-secreting cells that overcome limitations associated with current therapies. We have recently demonstrated durable correction of murine and porcine diabetes by syngeneic and autologous implantation, respectively, of primary hepatocytes non-virally modified with a glucose-responsive promoter-regulated insulin transgene. As surgical procurement of hepatocytes may be clinically unappealing, we here describe primary bone marrow-derived mesenchymal stromal cells (BMMSC) as alternative insulin-secreting bioimplants. BMMSC are abundant and less invasively procured for clinical autologous transplantation. Electroporation achieved high transgene transfection efficiencies in human BMMSC (HBMMSC) and porcine BMMSC (PBMMSC). We transcriptomically identified an HBMMSC glucose-responsive promoter, EGR1. This endogenously active promoter drove rapid glucose-induced transgene secretions in BMMSC with near-physiological characteristics during static and kinetic induction assays simulating normal human islets. Preparatory to preclinical transplantation, PBMMSC transfected with the circular insulin transgene vector or stably integrated with the linearized vector were evaluated by intrahepatic or intraperitoneal xenotransplantation in streptozotocin-diabetic and non-diabetic NOD-SCID mice. Hyperglycemia, glucose tolerance and body weight were corrected in a dose-responsive manner. Hypoglycemia was not observed even in identically implanted non-diabetic mice. These results establish human EGR1 promoter-insulin construct-modified BMMSC as safe and efficient insulin-secreting bioimplants for diabetes treatment.

Cells of extraembryonic mesodermal origin confer human dystrophin in the mdx model of Duchenne muscular dystrophy.

Duchenne muscular dystrophy is an X-linked recessive genetic disease characterized by severe skeletal muscular degeneration. The placenta is considered to be a promising candidate cell source for cellular therapeutics because it contains a large number of cells and heterogenous cell populations with myogenic potentials. We analyzed the myogenic potential of cells obtained from six parts of the placenta, that is, umbilical cord, amniotic epithelium, amniotic mesoderm, chorionic plate, villous chorion, and decidua basalis. In vitro cells derived from amniotic mesoderm, chorionic plate, and villous chorion efficiently transdifferentiate into myotubes. In addition, in vivo implantation of placenta-derived cells into dystrophic muscles of immunodeficient mdx mice restored sarcolemmal expression of human dystrophin. Differential contribution to myogenesis in this study may be attributed to placental portion-dependent default cell state. Molecular taxonomic characterization of placenta-derived maternal and fetal cells in vitro will help determine the feasibility of cell-based therapy.

Tracing of cells of the avian thymus through embryonic life in interspecific chimeras.

Differences in the structure of the interphase nucleus between two species of birds, the Japanese quail (Coturnix coturnix japonica) and the chick (Gallus gallus) has been used to distinguish cells from different origins in interspecies combinations. This biological cell marking technique was applied to thymus histogenesis. Using various combinations between components of quail and chick thymic rudiments, the respective contribution of endodermal epithelium, mesenchyme, and blood-borne extrinsic elements to the histogenesis of thymus was analyzed. It was demonstrated that the whole lymphoid population of the thymus is derived from immigrant blood-borne stem cells which are chemically attracted by the endoderm of the 3rd and 4th pharyngeal pouch. The latter is determined to differentiate into thymic epithelial reticulum as soon as the 15-somite stage, and is able to attract blood stem cells even when transplanted in an heterotopic position such as the ventral body wall of the embryo. It was shown that the thymic mesenchyme originates from the neural crest mesectoderm which colonizes early the 3rd and 4th branchial arches. It participates in the formation of perivascular mesenchyme, but does not give rise to lymphocytes. From heterospecific transplantations of quail thymuses into chick embryo (and inversely) at various stages of development is appeared that the thymic rudiment becomes attractive for lymphoid stem cells at a precise stage of its evolution for each species. The attractivity period lasts about 24 h for the quail and 36 h for the chick. Then, the inflow of stem cells becomes very low until the end of the incubation period. At this time, a second wave of lymphocytoblasts invades the thymus and the primitive embryonic lymphoid population is completely renewed around the hatching time. Competent thymic stem cells are present in the blood before and after the period of physiological thymic attractivity. The identity of basophilic cells appearing in the thymus during its histogenesis and lymphoid stem cells has been demonstrated from the analysis of quail-chick chimeric thymuses.

Endodermal origin of bladder trigone inferred from mesenchymal-epithelial interaction.

PURPOSE: In the classic view of bladder development the trigone originates from the mesoderm derived wolffian ducts while the remainder of the bladder originates from the endoderm derived urogenital sinus. Recent molecular developmental studies have questioned the veracity of this received wisdom, suggesting an endodermal origin for the trigone. To shed further light on this issue we observed mesenchymal-epithelial interactions between trigone epithelium and fetal urogenital sinus mesenchyma to infer the trigonal germ layer of origin. MATERIALS AND METHODS: Mouse trigone epithelium was recombined with fetal rat urogenital sinus mesenchyma in tissue recombinant grafts that were placed beneath the renal capsule of athymic mouse hosts. Grafts were harvested at 4 weeks. Control grafts with bladder dome and ureteral epithelium were also examined. Tissues were evaluated with hematoxylin and eosin, and Hoechst dye 33258 to confirm cell species origin. Immunohistochemistry was done with androgen receptor, broad spectrum uroplakin, dorsolateral prostate secretions and seminal vesicle secretions to differentiate prostatic and seminal vesicle differentiation. RESULTS: Grafts of mouse trigone epithelium with fetal rat urogenital sinus mesenchyma yielded epithelial tissue that stained for dorsolateral prostate secretions but not for seminal vesicle secretions. Control grafts of bladder dome epithelium yielded the expected endodermal prostate differentiation. Control grafts of ureteral epithelium yielded the expected mesodermal seminal vesicle differentiation. CONCLUSIONS: The consistent finding of prostatic epithelium in tissue recombinants of trigone epithelium and fetal urogenital sinus mesenchyma reinforces the hypothesis that the trigone is derived from the endoderm and not from the mesoderm, as commonly accepted.

Further proof of the plasticity of adult stem cells and their role in tissue repair.

In this issue, De Bari et al. (2003) present elegant data to counter the recent claims that adult stem cells have a limited plasticity. Further, they provide evidence that adult stem cells can seek out damaged tissues and repair them.

Skeletal muscle repair by adult human mesenchymal stem cells from synovial membrane.

We have demonstrated previously that adult human synovial membrane-derived mesenchymal stem cells (hSM-MSCs) have myogenic potential in vitro (De Bari, C., F. Dell'Accio, P. Tylzanowski, and F.P. Luyten. 2001. Arthritis Rheum. 44:1928-1942). In the present study, we have characterized their myogenic differentiation in a nude mouse model of skeletal muscle regeneration and provide proof of principle of their potential use for muscle repair in the mdx mouse model of Duchenne muscular dystrophy. When implanted into regenerating nude mouse muscle, hSM-MSCs contributed to myofibers and to long term persisting functional satellite cells. No nuclear fusion hybrids were observed between donor human cells and host mouse muscle cells. Myogenic differentiation proceeded through a molecular cascade resembling embryonic muscle development. Differentiation was sensitive to environmental cues, since hSM-MSCs injected into the bloodstream engrafted in several tissues, but acquired the muscle phenotype only within skeletal muscle. When administered into dystrophic muscles of immunosuppressed mdx mice, hSM-MSCs restored sarcolemmal expression of dystrophin, reduced central nucleation, and rescued the expression of mouse mechano growth factor.

Compensation mechanism in tumor cell migration: mesenchymal-amoeboid transition after blocking of pericellular proteolysis.

Invasive tumor dissemination in vitro and in vivo involves the proteolytic degradation of ECM barriers. This process, however, is only incompletely attenuated by protease inhibitor-based treatment, suggesting the existence of migratory compensation strategies. In three-dimensional collagen matrices, spindle-shaped proteolytically potent HT-1080 fibrosarcoma and MDA-MB-231 carcinoma cells exhibited a constitutive mesenchymal-type movement including the coclustering of beta 1 integrins and MT1-matrix metalloproteinase (MMP) at fiber bindings sites and the generation of tube-like proteolytic degradation tracks. Near-total inhibition of MMPs, serine proteases, cathepsins, and other proteases, however, induced a conversion toward spherical morphology at near undiminished migration rates. Sustained protease-independent migration resulted from a flexible amoeba-like shape change, i.e., propulsive squeezing through preexisting matrix gaps and formation of constriction rings in the absence of matrix degradation, concomitant loss of clustered beta 1 integrins and MT1-MMP from fiber binding sites, and a diffuse cortical distribution of the actin cytoskeleton. Acquisition of protease-independent amoeboid dissemination was confirmed for HT-1080 cells injected into the mouse dermis monitored by intravital multiphoton microscopy. In conclusion, the transition from proteolytic mesenchymal toward nonproteolytic amoeboid movement highlights a supramolecular plasticity mechanism in cell migration and further represents a putative escape mechanism in tumor cell dissemination after abrogation of pericellular proteolysis.

Specification of the zebrafish nervous system by nonaxial signals.

The organizer of the amphibian gastrula provides the neurectoderm with both neuralizing and posteriorizing (transforming) signals. In zebrafish, transplantations show that a spatially distinct transformer signal emanates from tissues other than the organizer. Cells of the germring (nonaxial mesendoderm) posteriorized forebrain progenitors when grafted nearby, resulting in an ectopic hindbrain-like structure; in contrast, cells of the organizer (axial mesendoderm) caused no posterior transformation. Local application of basic fibroblast growth factor, a candidate transformer in Xenopus, caused malformation but not hindbrain transformation in the forebrain. Thus, the zebrafish gastrula may integrate spatially distinct signals from the organizer and the germring to pattern the neural axis.

Transformation of tooth type induced by inhibition of BMP signaling.

Mammalian dentitions are highly patterned, with different types of teeth positioned in different regions of the jaws. BMP4 is an early oral epithelial protein signal that directs odontogenic gene expression in mesenchyme cells of the developing mandibular arch. BMP4 was shown to inhibit expression of the homeobox gene Barx-1 and to restrict expression to the proximal, presumptive molar mesenchyme of mouse embryos at embryonic day 10. The inhibition of BMP signaling early in mandible development by the action of exogenous Noggin protein resulted in ectopic Barx-1 expression in the distal, presumptive incisor mesenchyme and a transformation of tooth identity from incisor to molar.

The location and characteristics of two populations of dental pulp cells affect tooth development.

This study investigated the characteristics of two dental pulp cell populations during the early stages of crown formation in porcine teeth. A transplantation method was developed to reproduce epithelial cell-mesenchymal cell interactions during odontogenesis (tooth development). The technique allowed two types of cells/tissue to be combined in vivo. Populations of cells localized in the cervical loop epithelium region, dental pulp horn, and dental pulp core chambers were isolated and dissociated into single cells. Each population was examined for its gene-expression pattern using both semiquantitative and quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses, and for its tissue-formation capability by combining the cervical loop epithelial cells with either pulp horn cells or pulp core cells on biodegradable collagen scaffolds that were subsequently examined using histology and immunohistology. Gene-expression patterns showed that pulp horn cells were more mature than pulp core cells. Cervical loop epithelial cells combined with pulp horn cells mainly reconstituted dentin-cementum structures. By contrast, cervical loop epithelial cells combined with pulp core cells reconstituted enamel-dentin structures. These results suggest that mesenchymal cells residing in a specific location of the pulp possess a specific tissue-formation potential when combined with epithelial cells.

Differential response of immortalized human amnion mesenchymal and epithelial cells against oxidative stress.

Cells are equipped with various antioxidant defense factors to antagonize insults from reactive oxygen species (ROS), thus the antioxidant capacity has been characterized by a variety of cellular responses during the pathophysiological processes. Amniotic cells have been extensively applied in clinical practice for burn treatment, corneal repair, and tissue regeneration. However, the antioxidative properties of amniotic cells have not yet been fully understood. Therefore, the current study was aimed to observe the response of amniotic cells against ROS stimuli, and to investigate the underlying molecular mechanisms. The immortalized human amniotic mesenchymal cells (iHAMs) and immortalized human amniotic epithelial cells (iHAEs) were used. The human skin fibroblast (HSF) was used as a control cell line. Changes in intracellular ROS generation, cell viability, and cellular morphology were investigated to reveal the response of amniotic cells against oxidative stresses induced by x-rays and hydrogen peroxide. In addition, expression of apoptosis-related proteins and response to antioxidative stress was also examined. The intracellular ROS level and cell apoptosis in iHAMs was remarkably increased. iHAEs showed relatively high resistance to ROS stimulation, which can be attributed to the high SOD2 expression and up-regulation of Nrf2, HO-1 after x-rays exposure. In contrast, iHAMs were found sensitive to oxidative damage. Expression of caspase-3, caspase-8 and BAX was increased, whereas down-regulation of Bcl-xL, Nrf2, HO-1, and TrxR-1. Taken together, findings have highlighted the characterization of response of amniotic derived epithelial and mesenchymal cells to oxidative stress. In physiological processes, iHAMs may play an important role to maintain the homeostasis of the pregnancy environment. However, under oxidative stimulations, iHAEs provides protection against oxidative damage in amnion tissue.

Mesenchymal cell fusion in the sea urchin embryo.

Mesenchymal cells of the sea urchin embryo provide a valuable experimental model for the analysis of cell-cell fusion in vivo. The unsurpassed optical transparency of the sea urchin embryo facilitates analysis of cell fusion in vivo using fluorescent markers and time-lapse three-dimensional imaging. Two populations of mesodermal cells engage in homotypic cell-cell fusion during gastrulation: primary mesenchyme cells and blastocoelar cells. In this chapter, we describe methods for studying the dynamics of cell fusion in living embryos. These methods have been used to analyze the fusion of primary mesenchyme cells and are also applicable to blastocoelar cell fusion. Although the molecular basis of cell fusion in the sea urchin has not been investigated, tools have recently become available that highlight the potential of this experimental model for integrating dynamic morphogenetic behaviors with underlying molecular mechanisms.

Effect of whole bone marrow cell infusion in the progression of experimental chronic renal failure.

INTRODUCTION: The therapeutic potential of adult stem cells for the treatment of chronic diseases is becoming increasingly evident over the last few years. In the present study, we sought to assess whether the infusion of bone marrow-derived mononuclear cells (MoSCs) and mesenchymal cells (MSCs) could reduce/stabilize the rate of progression of chronic renal failure (CRF) in rats. METHODS: We used the 5/6 renal mass reduction model to induce chronic renal failure in male Wistar rats. Renal function was assessed by measurements of serum creatinine (sCr), creatinine clearance (Clcr), and 24-hour proteinuria at baseline as well as 60 and 120 days after surgery. MoSCs and MSCs obtained from bone marrow aspirates were separated by the Ficoll-Hypaque method. After a 12- to 14-day culture, 1.5 x 10(6) MSCs and the same number of MoSCs were injected into the renal parenchyma of the remanant kidney of rats with CRF on the day of surgery. RESULTS: Among the control group, at day 120, the results were sCr = 1.31 +/- 0.5 mg/dL, Clcr = 0.64 +/- 0.35 mL/min, and proteinuria = 140.0 +/- 57.7 mg/24 h. Rats treated with MoSCs at day 120 had sCr = 0.81 +/- 0.20 mg/dL, Clcr = 1.05 +/- 0.26 mL/min, and proteinuria = 61 +/- 46.5 mg/24 h, while rats injected with MSCs had sCr = 0.95 +/- 0.1 mg/dL, Clcr = 0.68 +/- 0.24 mL/min, and proteinuria = 119.2 +/- 50.0 mg/24 h. Analysis of the progression to CRF showed that the treatment significantly reduced the rate of decline in Clcr after treatment with MoSc: control: -0.0049 +/- 0.0024 mL/min/d versus MSC: - 0.0013 +/- 0.0017 mL/min/d versus MoSC: +0.0002 +/- 0.0016 mL/min/d (P = .017). Proteinuria tended to be lower among the treated groups. Histological scores of chronic damage were not different, but distinct patterns of chronic lesions were observed among treated rats. CONCLUSION: Our results showed that progression of CRF in rats could be slowed/stabilized by intrarenal parenchymal injection of MoSCs. A trend toward reduction in the progression rate of CRF was also observed with injection of MSCs.

[Protective effects of metanephric mesenchymal cells on acute renal tubular damage: experiment with rats].

OBJECTIVE: To study the protective effects of metanephric mesenchymal cells (MMCs) on acute renal tubular damage and explore its possible mechanism. METHODS: MMCs were isolated and cultured from 13-day-old embryonic rats and labeled with 5-bromodeoxyuridine. Seventy-two male SD rats were randomly divided into 3 equal groups: MMC group, receiving MMC injection instantaneously when ischemia/reperfusion (I/R) renal injury was induced, I/R group, undergoing I/R to establish acute renal tubular damage models, and sham operation group. Six rats from each group were killed at different time points: 24 h, 48 h, 72 h, and 96 h later. Blood sample was collected from the vena cava inferior, to examine the serum creatinine (SCr) and blood urea nitrogen (BUN). Specimens of kidney underwent microscopy. Apoptosis was conformed by TUNEL assay. Immunohistochemistry was used to detect the protein expression of Bcl-2 and Bax. The distribution of MMCs labeled with 5-bromodeoxyuridine in kidney was observed by immunofluorescence technique. RESULTS: The SCr and BUN levels in different time points of the MMC group were both significantly lower than those of the I/R group (both P <0.05), HE staining showed that pathological damage of the MMC group was less than that of the I/R group (P <0.05). TUNEL results investigated that the number of apoptosis renal tubular epithelial cells of the MMC group was (13.4 +/- 3.2/HPF), significantly less than that of the I/R group [(25.4 +/- 5.2/HPF)]. In comparison with the I/R group, there were more Bcl-2 positive cells and fewer Bax positive cells in the MMC group. BrdU-labeled MMCs began to occur in the renal tissue (60 +/- 6/HP) In the 72 h subgroup of MMC group, and number of BrdU-labeled MMCs, the 96 h subgroup was (143 +/- 8/HP), significantly higher than that of the 72 h subgroup (P<0.05). CONCLUSION: MMCs have the ability to protect renal function in acute renal tubular damage in rats, migrate and repopulate in the I/R injured renal tubules, and inhibits renal tubular epithelial cell apoptosis. The mechanism may be involved in regulating the expression of Bcl-2 and Bax.