1、Historical Perspectives and Advances in Mesenchymal Stem CellResearch for the Treatment of Liver DiseasesChien-Wei Lee,1,2Yu-Fan Chen,2,3Hao-Hsiang Wu,2,4and Oscar K.Lee2,3,5,61Program in Molecular Medicine,National Yang-Ming University and Academia Sinica,Taipei,Taiwan;2Stem Cell ResearchCenter,Nat
2、ional Yang-Ming University,Taipei,Taiwan;3Institute of Clinical Medicine,National Yang-Ming University,Taipei,Taiwan;4Institute of Biophotonics,National Yang-Ming University,Taipei,Taiwan;5Department of Medical Research,TaipeiVeterans General Hospital,Taipei,Taiwan;and6Taipei City Hospital,Taipei,Ta
3、iwanLiver transplantation is the only effective therapy forpatients with decompensated cirrhosis and fulminant liverfailure.However,due to a shortage of donor livers andcomplications associated with immune suppression,thereis an urgent need for new therapeutic strategies forpatients with end-stage l
4、iver diseases.Given their uniquefunction in self-renewal and differentiation potential,stemcells might be used to regenerate damaged liver tissue.Recent studies have shown that stem cellLbased therapiescan improve liver function in a mouse model of hepaticfailure.Moreover,acellular liver scaffolds s
5、eeded withhepatocytes produced functional bioengineered livers fororgan transplantation in preclinical studies.The thera-peutic potential of stem cells or their differentiated prog-enies will depend on their capacity to differentiate intomature and functional cell types after transplantation.Itwill
6、also be important to devise methods to overcome theirgenomic instability,immune reactivity,and tumorigenicpotential.We review directions and advances in the use ofmesenchymal stem cells and their derived hepatocytesfor liver regeneration.We also discuss the potentialapplications of hepatocytes deriv
7、ed from human pluripo-tent stem cells and challenges to using these cells intreating end-stage liver disease.Keywords:StemCellTherapy;PluripotentStemCells;Hepatocytes;Regenerative Medicine.Despitethesuccessoftransplantationofhematopoietic stem cells,few other cell-basedtherapies have been successful
8、ly translated into clinicalapplication.The dearth of cell-based therapies is unfortu-nate,as the potential and demand for such therapiesare apparent.One field with exciting developments incell-based therapies is the field of liver diseases.Acuteliverfailure,end-stageliverdiseases,andinherited metabo
9、lic disorders usually lead to morbidity andmortality,and are associated with a variety of etiologies(eg,toxic injury,viral infections,and autoimmune andgenetic disorders).In the United States,approximately30,000 deaths each year are caused by chronic liver disease;the incidence of such deaths increa
10、ses by 3%each year.1The only curative treatment for end-stage liver disease isliver transplantation.However,there are 15,000 patientson the wait list for a liver in the United Statesapproximately 50%of them will not receive a transplant.Liver disease is the leading cause of premature death in theUni
11、ted Kingdom,resulting in the loss of a greater number oflife-years than many other causes.2Liver transplantation,the best treatment option,is limited by high cost andshortage of donor organs.In addition,long-term survivalis hampered by graft-vs-host disease and side effects oflife-long immunosuppres
12、sion.3Transplantation of hepatocytes has been consideredas an alternative to transplantation of organs,but facesmultiple problems,including the shortage of high-quantitycell sources,challenges to expansion in vitro,concerns ofallogeneic rejection and xenozoonosis,and the fact thathepatocytes spontan
13、eously and quickly lose hepatic charac-teristics in vitro.46Stem cells,including induced pluripotentstemcells(iPSCs),mesenchymalstemcells(MSCs),fetal liverstem cells,fetal biliary tree stem cells,chemically inducedliver progenitors,and bone marrow CD45cells,could pro-vide alternatives to organ and h
14、epatocyte transplantation,andmayoffersolutionstotheproblemsmentioned.7,8Amongthem,MSCs have been investigated in detail and hold greatpromiseforclinicalapplication,asapersonalizedcelltherapy.This is because they can be conveniently isolated andexpanded in culture,are immune modulatory,and allogeneic
15、cells to not pose a xenozoonosis risk.MSCs also providetrophic support,have the potential to differentiate intohepatocyte-like cells(HLCs),and there are no ethical issuesare associated with their use.911We review the role of MSCsin HLC generation and liver regenerative medicine,and pointto new techn
16、ologies for clinical application.In Treatment of Liver DiseaseMSCs were first isolated from the bone marrow in 1968,by Friedenstein et al.12These cells can be also isolated fromother adult somatic tissues,such as the adipose tissue andumbilical cord blood.Given the self-renewal abilities of MSC,and
17、their therapeutic potential in tissue engineering andAbbreviations used in this paper:BAL,bioartificial liver system;CCl4,carbon tetrachloride;3D,3-dimensional;ECM,extracellular matrix;HESC,human embryonic stem cell;HGF,hepatocyte growth factor;HLC,hepatocyte-like cell;HPSC,human pluripotent stem ce
18、ll;HSC,hepaticstellate cell;IL,interleukin;iPSCs,induced pluripotent stem cells;MSC,mesenchymal stem cell;PSC,pluripotent stem cell.Most current article 2018 by the AGA Institute0016-5085/$36.00https:/doi.org/10.1053/j.gastro.2017.09.049Gastroenterology 2018;154:4656REVIEWS ANDPERSPECTIVESregenerati
19、ve medicine,MSCs are considered as an ideal cellsource for transplantation.The safety and feasibility ofMSC-based therapies have been demonstrated in clinicaltrials for many diseases,including graft-vs-host disease,heart diseases,osteoarthritis,bone and cartilage injuries,diabetes and its complicati
20、ons,cancer,spinal cord injury,multiple sclerosis,liver cirrhosis,respiratory disorders,Crohns disease,autoimmune diseases,and others.13MSCs can localize to damaged liver and eliminate liverfibrosis.Migration of MSCs is facilitated by release of severalmolecules from the damaged liver that interact w
21、ithdifferent receptors expressed by the MSCs.1416MSCs mightbe used to treat different types of liver disease because theytrans-differentiate in vitro and MSC-derived HLCs cansubstitute for injured hepatocytes to restore liver function,have immunosuppressive and anti-inflammatory effects,promotesurvi
22、valofresidenthepatocytes,anddirectdifferentiation in vivo(Figure 1).Hepatocyte DifferentiationTransplantedMSC-derivedHLCsincreasehepaticfunction at the engraftment site in models of acute andchronic liver failure.In 2004,Shu et al17demonstrated thedifferentiation of rat bone marrow MSCs into albumin
23、-andcytokeratin 18?expressing HLCs.In the same year,wereported a 2-step protocol for the induction of HLCs fromhuman bone marrow MSCsthese cells have hepatocyte-specific gene expression patterns and hepatocyte-specificfunctions,including urea and glycogen production.18Basedon these findings,successf
24、ul differentiation of MSCs fromother tissue origin into HLCs was also reported.HLCshavebeenderivedfromumbilicalcordbloodandbone marrow?derived MSCs.19,20Furthermore,adiposetissue?derived MSCs were also successfully induced todifferentiate into HLCs.21In the last decade,different groups established s
25、everalhepatic differentiation protocols for MSCs(summarized inTable 1).MSCs are more efficiently induced into HLCsin mice via a 2-step hepatic differentiation protocol18,21thanby the hepatic differentiation protocol described by Shuet al.17Transplantation of MSC-derived hepatocytes canrestore liver
26、function to mice with carbon tetrachloride(CCl4)-induced liver failure.22Co-culture of MSCs withprimary liver cells induces differentiation of MSCs intoHLCs.23MSC-derived HLCs,formed by co-culture with pri-mary hepatocytes,integrate into injured liver and reducefibrosis.24Incubation of MSCs with inj
27、ured liver tissue wasreported to increase expression of hepatocyte-specific genesin MSCs.25These observations provide evidence for alter-native methods of inducing differentiation of MSCs intoHLCs,via interactions with liver cells,and the possibility oftissue integration after stem cell transplantat
28、ion.Small Inhibitors in HepatocyteDifferentiationDifferentiation of MSCs into hepatocytes involves in themesenchymal to epithelial transition.An inhibitor of RAC1(NSC23766)maintains the epithelial morphology of MSCs,accelerates up-regulation of hepatocyte marker genes,andinduces hepatocyte cell func
29、tions,by altering actin poly-merization during differentiation.26Chromatin-remodelingagents,such as valproic acid,5-aza-20-deoxycytidine,andtrichostatin A,promote differentiation of MSCs into hepa-tocytes,indicating epigenetic regulation of this transition.hepatocytes.2729Manipulating hepatocyte dif
30、ferentiationof MSCs,via intracellular and extracellular factors,mightpromote hepatic maturation,accelerate cell differentiation,or increase proliferation.Mechanical Forces andMicroenvironment ArchitectureMechanicalforcesandthearchitectureofthemicroenvironmentaffectdifferentiationofMSCsintohepatocyte
31、s.Continuous flow of fluid over microfluidicchips increases the ability of MSCs to uptake low-densitylipoprotein as they differentiate into hepatocytes.30Lowshear stress increases differentiation of MSCs into hepa-tocytes.31To mimic the 3-dimensional(3D)microenvi-ronmentandarchitectureoftheliver,som
32、egroupsfabricated artificial 3D scaffolds and investigated whetherthey induce differentiation of MSCs more efficiently than2-dimensional culture.MSCs were reported to increasedifferentiation into hepatocytes on poly-caprolactone/collagen/polyethersulfonenanofiberscaffolds.32Poly-L-lactic acid nanofi
33、ber scaffolds were also reported toincrease the expression of hepatocyte-specific genes bydifferentiating MSCs.33Interestingly,during the differenti-ation of MSCs into hepatocytes on artificial 3D scaffolds,MSCs form hepatic spheroids that express markers ofhepatocytes and undergo glycogen storage,u
34、rea produc-tion,albumin secretion,and cytochrome P450 activity.34Despite reports indicating the potential of MSCs todifferentiate into hepatocytes,MSC-derived HLCs are similarto fetal hepatocytes and do not reach full maturity in vitro.33In addition,different types of stem cell sources for theinduct
35、ion of HLCs have been reported;these were generatedusing a modified differentiation protocol.35Therefore,thematuration process of MSCs during hepatic differentiationrequires improvement.Anti-Inflammatory EffectsThe liver is an immunologically complex organ.Itcontains specialized immune cells,includi
36、ng Kupffer cells;antigen-presenting liver sinusoidal endothelial cells anddendritic cells;and liver-resident lymphocytes.36In addi-tion,the hepatocytes and hepatic stellate cells(HSCs)affectthe immune response in the liver by activating T cells.3739The liver microenvironment and immune response main
37、tainliver homeostasis.Inflammation is one of the most characteristic featuresof different liver diseases and is present at all diseasestages.40MSCs modulate innate and adaptive immuneresponses.41MSC-derived prostaglandin E2 and indole-amine2,3-dioxygenasereducesproliferation,cytolyticJanuary 2018Ste
38、m Cell Therapy for Liver Diseases47REVIEWS ANDPERSPECTIVESFigure 1.Stem cell-based therapies for liver diseases.(1)MSCs modulate immuno-response and ameliorate ectopicinflammation.(2)MSCs repress fibrosis/cirrhosis in hepatic microenvironments.(3)MSCs provide trophic factors to regenerateor repair i
39、njury tissues.(4)Transplanted MSCs engraft and differentiate into hepatocytes in vivo.(5)iPSC-derived andMSC-derived functional hepatocyte-like cells substitute the damage hepatocytes.DC,dendritic cell;EV,extracellular vesicle;IDO,indoleamine 2,3-dioxygenase;MMP,matrix metalloproteinase;NGF,nerve gr
40、owth factor;PGE2,prostaglandin E2;TGF,transforming growth factor;TNF,tumor necrosis factor;Treg,regulatory T cell.48Lee et alGastroenterology Vol.154,No.1REVIEWS ANDPERSPECTIVESactivity,and cytokine secretion of natural killer cells.42MSCsalso repress the activity of Kupffer cells,reducing secretion
41、of the inflammatory cytokine tumor necrosis factor43;theyalsoconvertM1macrophages(inflammatory)toM2macrophages(anti-inflammatory),bysecretingprosta-glandin E2.44MSC-derived human leukocyte antigen Ginactivates dendritic cells45;MSC-derived interleukin(IL)6and hepatocyte growth factor(HGF)inhibit the
42、 maturationof monocytes into dendritic cells,reducing their inflamma-tory potential and changing activated CD4T cells fromT-helper 1 to T-helper 2 phenotypes.46MSCs also inhibitproliferation of CD8T cells and increase the rate of con-version of CD4T cells from T-helper 1 to T-helper 2phenotypes by s
43、ecreting heme oxygenase 1 and indoleamine2,3-dioxygenase.4750Furthermore,MSCs induce the devel-opment of regulatory T cells to modulate CD4T-cellpolarization.51MSCs directly inhibit B-cell proliferation and terminaldifferentiation through soluble factors and cell contacts.52MSCs also act as immunosu
44、ppressors after liver trans-plantation in mice.53Only a few studies reported the use ofimmunosuppression during liver transplantation,but theyindicated that liver transplantation with MSC infusion mightprevent acute rejection by regulating T-cell expansion andincreasing serum levels of IL10.5457MSC-
45、derived indole-amine 2,3-dioxygenase increases survival of patients withrefractory chronic graft-vs-host disease by stimulating CD5regulatory B cells to produce IL10;this is associated withreduced inflammatory cytokine production by T cells.58Collectively,MSCs convert the overall immune response tol
46、ess inflammatory(or more tolerant)response by alteringthe secretome of the immune cells.59Most of the immunomodulatory features of MSCs areattributed to their secretome and proteome.However,thespectrum of secretory factors of MSCs differs from that ofMSCs-derived hepatocyte-like cells and hepatocyte
47、s.27,60Although immunoregulation by MSCs participates in liverrepair and liver transplantation,43,54,61the immunomodu-latory features of MSCs are typically reported in otherorgansratherthanintheliver.Therefore,furtherinvestigations are indispensable to determine whetherimmunomodulation by MSCs is cr
48、ucial in liver regeneration.Anti-Fibrotic EffectsClinical chronic liver inflammation caused by viralinfection,alcoholic liver disease,nonalcoholic steatohepati-tis,and autoimmune diseases results in liver fibrosis andcirrhosis.62Hepatic inflammation activates HSCs to produceextracellular matrix(ECM)
49、;this precedes and promotesprogression of liver fibrosis.MSCs reduce or reverse liverfibrosis via their immunomodulatory and anti-inflammatoryeffects.63,64On the other hand,MSCs directly inactivateHSCs by secreting IL10 and tumor necrosis factor,andinduce HSC apoptosis through HGF,nerve growth facto
50、rsignaling via p75,and Fas?FasL pathway.65MSCs mighttherefore be used in treatment of hepatic fibrosis.65MSCscan degrade ECM directly,by secreting matrix metal-loproteinases,66or indirectly,by stimulating the immuneTable 1.Current Mesenchymal Stem Cell Hepatic Differentiation ProtocolsCell sourceDif
