title: MSCs: The Sentinel and Safe-Guards of Injury.
abstract: Mesenchymal stem cells (MSCs) were originally named because they could differentiate in a variety of mesenchymal phenotypes in culture. Evidence indicates that MSCs arise from perivascular cells, pericytes, when the blood vessels are broken or inflamed. These pericyte/MSCs are situated on every blood vessel in the body. The MSCs sense the micro-environment of the injury site and secrete site-specific factors that serve several important reparative functions: first, a curtain of molecules from the front of the MSCs provide a barrier from the interrogation of the over-aggressive immune system. Second, from the back of the MSCs, a different set of bioactive agents inhibit scar formation and establish a regenerative micro-environment. Third, if bacteria are sensed by the MSCs, they produce powerful protein antibiotics that kill the bacteria on contact. Last, the MSCs surround and encyst intruding solid objects like a piece of wood (a "splinter") or other foreign objects. The MSCs act as a combination paramedic and emergency room (ER) staff to survey the damage, isolate foreign components, stabilize the injured tissues, provide antibiotics and encysting protection before a slower, medicinal sequence can be initiated to regenerate the damaged tissue. The MSCs, thus, act as sentinels to safeguard the individual from intrusion and chronic injury. A societal treatment system has evolved, paramedics and ER procedures, which mirror in a macro-sense what MSCs orchestrate in a micro-sense. Key to this new understanding is that MSCs are not "stem cells," but rather as Medicinal Signaling Cells as the therapeutic agents.
authors.affiliation: Department of Biology, Skeletal Research Center, Case Western Reserve University, Cleveland, Ohio.
authors.forename: Arnold I
authors.initials: AI
authors.lastname: Caplan
mesh_terms: D001808:Blood Vessels / Q000254:growth & development* / Q000293:injuries / Q000473:pathology; D002454:Cell Differentiation / Q000235:genetics*; D060833:Cellular Microenvironment / Q000235:genetics; D002921:Cicatrix / Q000473:pathology; D006801:Humans; D045164:Mesenchymal Stem Cell Transplantation; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000378:metabolism; D020286:Pericytes / Q000166:cytology*; D044968:Regenerative Medicine