Ischemic brain injury represents a major cause of death worldwide with limited treatment options with a narrow therapeutic window. Accordingly, novel treatments that extend the treatment from the early neuroprotective stage to the late regenerative phase may accommodate a much larger number of stroke patients. To this end, stem cell-based regenerative therapies may address this unmet clinical need. Several stem cell therapies have been tested as potentially exhibiting the capacity to regenerate the stroke brain. Based on the long track record and safety profile of transplantable stem cells for hematologic diseases, bone marrow-derived mesenchymal stromal cells or mesenchymal stromal cells have been widely tested in stroke animal models and have reached clinical trials. However, despite the translational promise of MSCs, probing cell function remains to be fully elucidated. Recognizing the multi-pronged cell death and survival processes that accompany stroke, here we review the literature on MSC definition, characterization, and mechanism of action in an effort to gain a better understanding towards optimizing its applications and functional outcomes in stroke. / National Institutes of Health / Revisión por pares

The current gold standard of therapy for treatment of tibial fracture nonunion is iliac crest bone graft. However, this intervention is associated with significant morbidity to the donor site. Research into alternative interventions highlights the role of mesenchymal stem cells (MSCs). MSCs are capable of differentiating into mature, organized osseous tissue as well as recruiting local vascular cells. However, there are few prospective studies demonstrating the therapeutic potential of MSCs in fracture nonunion. The proposed study is a multicenter single-blinded controlled study of MSC application compared to iliac crest bone graft in the setting of fracture nonunion of the tibia. The study subjects will be evaluated at each return to care with mRUST radiographic scoring as well as Short-Form 12 evaluation of general health. These results will be correlated with MSC concentrations as assessed by FACS analysis. The data from this study will help to characterize MSCs as a possible therapeutic intervention in fracture nonunion.

Stroke is the leading cause of long-term disability costing the United States (US) health care system 34 billion dollars. However, stem cell based therapies have been shown to improve recovery after cortical injury by enhancing neural recovery and modulating immune responses (Lambertsen, Finsen, & Clausen, 2018; Orczykowski et al., 2018; Stonesifer et al., 2017). Specifically, reorganization of the motor circuit at the level of the spinal cord has been shown to improve functional recovery after injury (Christoph Wiessner; Weidner et al., 2001; Lee et al., 2004; Zai et al., 2009). In our study we used a non-human primate (NHP) model to study the neural recovery after cortical injury similar to damage from an ischemic stroke in the motor cortex with or without a systemic treatment of mesenchymal stem cell derived (MSCd) exosomes. We find a robust recovery in motor function within the first few weeks after injury including improved grasp patterns and faster retrieval times during behavioral tasks. Additionally, assessment of the cervical spinal cord (CSC) reveals decreased levels of sprouting axons from ipsilesional corticospinal tract (CST) and MAP2+ synapses in the contralesional ventral horn at 14 weeks post-injury, which correlates with improved retrieval latencies. We hypothesize that MSCd exosomes may encourage an earlier switch to anti-inflammatory and repair processes that reduces secondary damage in the cortex resulting in earlier pruning of axon collaterals and reducing the need for compensatory mechanisms of the spinal cord at 14 weeks post injury.

Les progrès dans la compréhension de la biologie osseuse ont permis d’identifier le rôle du système nerveux sensoriel dans la formation osseuse, le remodelage et la régénération tissulaire. Cependant, le rôle précis du système nerveux sensoriel sur la l’ostéogénèse reste encore méconnu. La première partie de ce travail a été d’analyser le rôle des neurones du ganglion de la racine dorsale (DRG) sur la différenciation ostéoblastique des cellules souches mésenchymateuse (MSCs). Pour répondre à cette question, nous avons utilisé une plate-forme microfluidique, qui tente de mimer l’innervation sensorielle du tissu osseux. Dans la seconde partie de cette étude, nous avons cherché à mieux caractériser la sous-population de neurones DRG impliqués dans la régulation directe de la différenciation des MSCs vers le lignage ostéoblastique. En conclusion, l’ensemble des résultats permettent de montrer que: i) les neurones sensoriels ont un effet positif et direct sur la différenciation ostéoblastique des cellules ostéoprogénitrices, ii) la voie de signalisation Wnt/β-caténine est impliquée dans cette transduction du signal; iii) cet effet est principalement régulé par des neurones sensorimoteur, iv) qui peuvent induire la libération locale de facteurs neuroactifs. / Advances in the understanding of bone biology have identified the sensory nervous system as a critical regulator in the orchestration of bone formation, remodeling, and repair. However, the precise role of the sensory nervous system on bone tissue, particularly on osteoprogenitor cells, remains unknown. Firstly, we were interested in clarifying whether dorsal root ganglion (DRG) neurons would be able to induce the osteoblast differentiation by acting directly on mesenchymal stem cells (MSCs). Afterwards, we attempted to understand whether the canonical Wnt signaling pathway could be implicated in the DRG neurons-induced osteoblastogenesis. In the second part of this study, we aimed at better characterizing the subset of DRG neurons involved in the direct regulation of osteoblast differentiation from MSCs. In this work we provide several novel insights: i) we show that sensory neurons have a positive and direct effect on osteoblast differentiation of osteoprogenitor cells, ii) by activating the Wnt/β-catenin signaling pathway; and iii) we suggest that this effect is mainly regulated by sensorimotor neurons, iv) which possibly mediate the local release of neuroactive factors.

Le couple CXCL12/CXCR4 joue un rôle essentiel dans le maintien de l’homéostasie des cellules souches et progéniteurs hématopoïétiques (CSPHs) et constitue un axe clé par lequel les niches et les CSPHs communiquent au sein de la moelle osseuse (MO). Des mutations hétérozygotes du gène CXCR4, qui tronquent le domaine C-terminal de la protéine et entraînent un défaut de désensibilisation homologue de CXCR4 et une hypersensibilité à CXCL12, ont été identifiées dans le Syndrome WHIM (SW), une immunodéficience rare caractérisée notamment par une lymphopénie. Les mécanismes sous-jacents de cette anomalie restaient inconnus. Grâce à un modèle murin porteur d’une mutation gain de fonction de Cxcr4 identifiée chez certains patients et phénocopiant la lymphopénie du SW, nous avons exploré la possibilité qu’un défaut de domiciliation, de différenciation ou d’expansion des CSPHs dans la MO soit à l’origine de la lymphopénie circulante. Nous avons mis en évidence que la désensibilisation de Cxcr4 régule la balance quiescence/cycle des CSHs à court terme ainsi que leur différenciation en progéniteurs multipotents et progéniteurs engagés vers le lignage lymphoïde. Nos travaux révèlent donc que la désensibilisation de Cxcr4 est requise à la différenciation lymphoïde des CSPHs et suggèrent que l’absence de ce processus soit à l’origine de la lymphopénie observée chez les souris mutantes et, par extrapolation, chez les patients. Ces altérations lymphoïdes impliquaient à la fois des défauts intrinsèques (CSPHs) et extrinsèques (stroma), ce qui nous a conduit à considérer l’impact de la mutation gain de fonction de Cxcr4 sur le stroma médullaire. Dans ce contexte, l’objectif principal de mon projet de thèse a consisté à investiguer à l’aide du modèle murin du SW le rôle de la désensibilisation de Cxcr4 dans le maintien des composantes mésenchymateuses au sein de la MO. Nos données ont permis de mettre en lumière que la désensibilisation de Cxcr4 est intrinsèquement requise à la régulation de l’équilibre quiescence/cycle des cellules souches mésenchymateuses (CSMs), ainsi qu’à la préservation de leur potentiel ostéogénique en contrôlant l'expression et la biodisponibilité de Cxcl12 de manière autocrine. Par conséquent, nos travaux suggèrent que les actions autocrines et paracrines de l’axe de signalisation Cxcl12/Cxcr4 au sein des CSMs régulent leur différenciation en ostéoblastes tout en contribuant au maintien des niches des CSPHs et au processus d’hématopoïèse. / The CXCL12/CXCR4 signaling axis plays an essential role in the maintenance of hematopoietic stem and progenitor cell (HSPC) homeostasis and constitutes a key pathway through which the niches and HSPCs communicate in the bone marrow (BM). Heterozygous gain-of-function mutations of CXCR4, which engender a truncated receptor and affect its homologous desensitization in response to CXCL12, have been reported in the WHIM Syndrome (WS); a rare immunodeficiency notably characterized by lymphopenia. The mechanisms underpinning this remain obscure. Using a mouse model harboring a naturally occurring WS-linked Cxcr4 gain-of-function mutation, we explored the possibility that the lymphopenia in WS arise from defects at the HSPC level in the BM. We showed that Cxcr4 desensitization is required for proper quiescence/cycling balance of short-term HSCs as well as their differentiation into multipotent progenitors and downstream lymphoid-biased progenitors. Thus, our results suggest that efficient Cxcr4 desensitization is critical for lymphoid differentiation of HSPCs, and its impairment is a key mechanism underpinning the lymphopenia observed in WS mice. The role of Cxcr4 desensitization in regulating such lympho-hematopoiesis process implicated both intrinsic and extrinsic properties, thus raising the question of the impact of a gain-of-Cxcr4-function mutation on BM stroma. Therefore, the main part of my PhD project was dedicated to evaluate using this relevant knock-in model the impact of Cxcr4 desensitization on maintenance of BM mesenchymal elements. We have found unexpectedly that such regulatory mechanism is intrinsically required for regulating quiescence/cycling balance of mesenchymal stem cells (MSCs) and preserving their osteogenic potential through the control of Cxcl12 expression and availability in an autocrine manner. Therefore, these findings support autocrine and paracrine actions of the Cxcl12/Cxcr4 signaling axis within MSCs to regulate osteoblast differentiation while contributing to HSPC niches and hematopoiesis.

Indiana University-Purdue University Indianapolis (IUPUI) / Mesenchymal stem cells (MSCs) are responsive to mechanical stimuli that play an essential role in directing their differentiation to the chondrogenic lineage. A better understanding of the mechanisms that allow MSCs to respond to mechanical stimuli is important to improving cartilage tissue engineering and regenerative medicine. Hydrostatic pressure (HP) in particular is known to be a primary mechanical force in joints. However, little is known about the underlying mechanisms that facilitate HP mechanotransduction. Understanding the signaling pathways in MSCs in transducing HP to a beneficial biologic response and their interrelationship were the focus of this thesis. Studies used porcine marrow-derived MSCs seeded in agarose gel. Calcium ion Ca++ signaling, focal adhesion kinase (FAK) involvement, and sirtuin1 activity were investigated in conjunction with HP application. Intracellular Ca++ concentration was previously shown to be changed with HP application. In our study a bioreactor was used to apply a single application of HP to the MSC-seeded gel structures and observe Ca++ signaling via live imaging of a fluorescent calcium indicator in cells. However, no fluctuations in Ca++ concentrations were observed with 10 minutes loading of HP. Additionally a problem with the biore actor design was discovered. First the gel was floating around in the bioreactor even without loading. After stabilizing the gel and stopping it from floating, there were still about 16 µm of movement and deformation in the system. The movement and deformation was analyzed for the gel structure and different parts of the bioreactor. Furthermore, we investigated the role of FAK in early and late chondrogenesis and also its involvement in HP mechanotransduction. A FAK inhibitor was used on MSCs from day 1 to 21 and showed a dose-dependent suppression of chondrogenesis. However, when low doses of FAK inhibitor added to the MSC culture from day 21 to 42, chondrogenesis was not inhibited. With 4 hour cyclic HP, FAK phosphorylation increased. The beneficial effect of HP was suppressed with overnight addition of the FAK inhibitor to MSC medium, suggesting FAK involvement in HP mechanotransd ucation by MSCs. Moreover, sirtuin1 participation in MSC chondrogenesis and mechanotransduc tion was also explored. The results indicated that overnight sirtuin1 inhibition in creased chondrogenic gene expression (Agc, Col2, and Sox9) in MSCs. Additionally, the activity of sirtuin1 was decreased with both 4 hour cyclic hydrostatic pressure and inhibitor application. These two together demonstrated that sirtuin1 inhibition enhances chondrogenesis. In this research we have investigated the role of Ca++ signaling, FAK involvement, and sirtuin1 activity in the mechanotransduction of HP in MSCs. These understand ings about the mechanisms regulating the chondrogenesis with respect to HP could have important implications for cartilage tissue engineering and regenerative studies.

Indiana University-Purdue University Indianapolis (IUPUI) / Dynamic changes to the extracellular matrix (ECM) impact many cell fate pro- cesses. The ECM can experience changes in sti ness as well as changes in composi- tion in response to injury, development, and diseases. To better understand the role that these dynamic processes have on the cells residing within the environment, re- searchers have turned towards 4-dimensional (4D) hydrogel designs. These 4D hydro- gels re-capitulate not only 3-dimensional (3D) matrix architectures, but also temporal changes in the physicochemical properties. The goal of this thesis was to design a unify chemistry (i.e., Sortase A (SrtA)-mediated transpeptidation) for dynamic tun- ing hydrogel sti ness and the presence of bioactive ligands. The rst objective was to establish a tunable and cytocompatible enzymatic scheme for softening cell-laden hydrogels. Brie y, the e ects of SrtA-mediated matrix cleavage were investigated us- ing poly(ethylene glycol) (PEG)-peptide hydrogels crosslinked by SrtA-sensitive and insensitive peptides. Initially, the e ects of various parameters with respect to cat- alytic reactions of SrtA were characterized rheologically, including enzyme and sub- strate concentrations, macromer content, peptide composition, and treatment time. Gel moduli pre- and post-enzyme treatment were measured to verify SrtA-mediated hydrogel softening. The cytocompatibility of SrtA-mediated gel softening system was investigated using human mesenchymal stem cell (hMSC). Upon treatment with SrtA and an oligoglycine substrate, encapsulated hMSCs exhibited extensive spreading in comparison to those within statically sti matrices. The second objective was to es- tablish a reversible ligand exchange system utilizing SrtA-mediated transpeptidation. SrtA-sensitive pendant ligands were immobilized within PEG hydrogels, which were treated with SrtA and an oligoglycine substrate to a ord tunable removal of the pen- dant ligand. Through measurement of the liberated pendant peptide concentration, it was found that higher concentrations of SrtA or extending treatment times led to higher ligand removal e ciency. Finally, the e ect of peptide ligand removal on cell behaviors were evaluated using NIH 3T3 broblasts. Fibroblasts were culture both on and within hydrogels containing SrtA-cleavable cell adhesion peptide. After treatment, both conditions led to a decrease in broblast spreading in comparison to non-treated gels. Overall, the utility of SrtA as versatile agent for controlling the mechanical properties and the presence of biologically active components within a hydrogel system was demonstrated. These systems could be further explored with natural-based materials to better mimic the physiological environment experienced by cells.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第17976号 / 医博第3840号 / 新制||医||1001(附属図書館) / 80820 / 京都大学大学院医学研究科医学専攻 / (主査)教授 戸口田 淳也, 教授 宮地 良樹, 教授 長澤 丘司 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第12831号 / 論医博第2080号 / 新制||医||1005(附属図書館) / 31369 / (主査)教授 川口 義弥, 教授 柳田 素子, 教授 小川 修 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第12944号 / 論医博第2096号 / 新制||医||1010(附属図書館) / 32203 / 京都大学大学院医学研究科医科学専攻 / (主査)教授 川口 義弥, 教授 横出 正之, 教授 稲垣 暢也 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM