Zerina Lokmic

Comparative Analysis of Paracrine Factor Expression in Human Adult Mesenchymal Stem Cells Derived from Bone Marrow, Adipose, and Dermal Tissue

Human adult mesenchymal stem cells (MSCs) support the engineering of functional tissue constructs by secreting angiogenic and cytoprotective factors, which act in a paracrine fashion to influence cell survival and vascularization. MSCs have been isolated from many different tissue sources, but little is known about how paracrine factor secretion varies between different MSC populations. We evaluated paracrine factor expression patterns in MSCs isolated from adipose tissue (ASCs), bone marrow (BMSCs), and dermal tissues [dermal sheath cells (DSCs) and dermal papilla cells (DPCs)]. Specifically, mRNA expression analysis identified insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor-D (VEGF-D), and interleukin-8 (IL-8) to be expressed at higher levels in ASCs compared with other MSC populations whereas VEGF-A, angiogenin, basic fibroblast growth factor (bFGF), and nerve growth factor (NGF) were expressed at comparable levels among the MSC populations examined. Analysis of conditioned media (CM) protein confirmed the comparable level of angiogenin and VEGF-A secretion in all MSC populations and showed that DSCs and DPCs produced significantly higher concentrations of leptin. Functional assays examining in vitro angiogenic paracrine activity showed that incubation of endothelial cells in ASC(CM) resulted in increased tubulogenic efficiency compared with that observed in DPC(CM). Using neutralizing antibodies we concluded that VEGF-A and VEGF-D were 2 of the major growth factors secreted by ASCs that supported endothelial tubulogenesis. The variation in paracrine factors of different MSC populations contributes to different levels of angiogenic activity and ASCs maybe preferred over other MSC populations for augmenting therapeutic approaches dependent upon angiogenesis.

Bisphosphonate-associated jawbone osteonecrosis: a correlation between imaging techniques and histopathology

OBJECTIVESnRecently, jawbone osteonecrosis has been reported as a potential adverse effect of bisphosphonates administration. This paper considers and highlights histopathologic and radiologic features of this condition.nnnSTUDY DESIGNnEleven patients, owing to unresponsiveness to conservative treatment and uncontrollable pain, underwent surgical resection of diseased jawbone after extensive hyperbaric oxygen therapy. A thorough clinical, laboratory, and imaging study was performed. Surgical specimens underwent histopathologic and immunohistochemical evaluation.nnnRESULTSnComputerized tomography (CT) scans showed increased bone density, periosteal reaction, and bone sequestration in advanced stages. With magnetic resonance imaging (MRI), exposed areas showed a low signal in T1- and T2-weighted and inversion recovery images, which suggests low water content and is histopathologically correlated with paucity in cells and vessels (osteonecrotic pattern). Unexposed diseased bone was characterized by T1 hypointensity and T2 and IR hyperintensity, which suggests high water content and inflammation, associated with hypercellularity, osteogenesis, and hypervascularity (osteomyelitic pattern).nnnCONCLUSIONSnDiseased bone extends beyond the limits of the bone exposed in the oral cavity. Histopathologic examination correlated well with CT and MRI, which are the choice for the evaluation of bisphosphonate-associated jawbone osteonecrosis.

An arteriovenous loop in a protected space generates a permanent, highly vascular, tissue-engineered construct.

A major obstacle to 3‐dimensional tissue engineering is incorporation of a functional vascular supply to support the expanding new tissue. This is overcome in an in vivo intrinsic vascularization model where an arteriovenous loop (AVL) is placed in a noncollapsible space protected by a polycarbonate chamber. Vascular development and hypoxia were examined from 3 days to 112 days by vascular casting, morphometric, and morphological techniques to understand the models vascular growth and remodeling parameters for tissue engineering purposes. At 3 days a fibrin exudate surrounded the AVL, providing a scaffold to migrating inflammatory, endothelial, and mesenchymal cells. Capillaries formed between 3 and 7 days. Hypoxia and cell proliferation were maximal at 7 days, followed by a peak in percent vascular volume at 10 days (23.2±03.14% compared with 3.5±92.68% at 3 days, P<0.001). Maximal apoptosis was observed at 112 days. The protected space and spontaneous microcirculatory development in this model suggest it would be applicable for in vivo tissue engineering. A temporal window in a period of intense angiogenesis at 7 to 10 days is optimal for exogenous cell seeding and survival in the chamber, potentially enabling specific tissue outcomes to be achieved.—Lokmic, Z., Stillaert, F., Morrison, W. A., Thompson, E. W., Mitchell, G. M. An arteriovenous loop in a protected space generates a permanent, highly vascular, tissue‐engineered construct. FASEB J. 21, 511–522 (2007)

Engineering the Microcirculation

The ultimate survival of tissue-engineered constructs in vivo depends on the provision of an adequate blood supply to the engineered tissue and the capacity of the engineered microcirculation to connect with the existing recipient circulation. Techniques for the vascularization of tissue-engineered constructs can be broadly grouped into in vitro and in vivo approaches that rely on the presence of a pro-angiogenic microenvironment. Significant advances have been made in resolving the problem of microcirculatory network formation for large 3-dimensional constructs; however, issues concerning construct-host vessel connection, expansion of vascular volume accompanying growing tissue, and prevention of premature or excessive vascular regression remain to be resolved. This review provides an overview of current approaches to creating microcirculatory networks with respect to the cells involved, growth factors, growth factor delivery systems, and scaffold properties required to engineer a permanent microcirculatory network for tissue-engineered constructs. In addition, the review examines concerns related to vascular remodeling and regression reported in some tissue-engineering models.

Hypoxia and hypoxia signaling in tissue repair and fibrosis.

Following injury, vascular damage results in the loss of perfusion and consequent low oxygen tension (hypoxia) which may be exacerbated by a rapid influx of inflammatory and mesenchymal cells with high metabolic demands for oxygen. Changes in systemic and cellular oxygen concentrations induce tightly regulated response pathways that attempt to restore oxygen supply to cells and modulate cell function in hypoxic conditions. Most of these responses occur through the induction of the transcription factor hypoxia-inducible factor-1 (HIF-1) which regulates many processes needed for tissue repair during ischemia in the damaged tissue. HIF-1 transcriptionally upregulates expression of metabolic proteins (GLUT-1), adhesion proteins (integrins), soluble growth factors (TGF-β and VEGF), and extracellular matrix components (type I collagen and fibronectin), which enhance the repair process. For these reasons, HIF-1 is viewed as a positive regulator of wound healing and a potential regulator of organ repair and tissue fibrosis. Understanding the complex role of hypoxia in the loss of function in scarring tissues and biology of chronic wound, and organ repair will aid in the development of pharmaceutical agents that can redress the detrimental outcomes often seen in repair and scarring.

The extracellular matrix of the spleen as a potential organizer of immune cell compartments.

Until recently little information was available on the molecular details of the extracellular matrix (ECM) of secondary lymphoid tissues. There is now growing evidence that these ECMs are unique structures, combining characteristics of basement membranes and interstitial or fibrillar matrices, resulting in scaffolds that are strong and highly flexible and, in certain secondary lymphoid compartments, also forming conduit networks for rapid fluid transport. This review will address the structural characteristics of the ECM of the murine spleen and its potential role as an organizer of immune cell compartments, with reference to the lymph node where relevant.

Time course analysis of hypoxia, granulation tissue and blood vessel growth, and remodeling in healing rat cutaneous incisional primary intention wounds.

Hypoxia and the development and remodeling of blood vessels and connective tissue in granulation tissue that forms in a wound gap following full‐thickness skin incision in the rat were examined as a function of time. A 1.5u2003cm‐long incisional wound was created in rat groin skin and the opposed edges sutured together. Wounds were harvested between 3 days and 16 weeks and hypoxia, percent vascular volume, cell proliferation and apoptosis, α‐smooth muscle actin, vascular endothelial growth factor‐A, vascular endothelial growth factor receptor‐2, and transforming growth factor‐β1 expression in granulation tissue were then assessed. Hypoxia was evident between 3 and 7 days while maximal cell proliferation at 3 days (123.6±22.2u2003cells/mm2, p<0.001 when compared with normal skin) preceded the peak percent vascular volume that occurred at 7 days (15.83±1.10%, p<0.001 when compared with normal skin). The peak in cell apoptosis occurred at 3 weeks (12.1±1.3u2003cells/mm2, p<0.001 when compared with normal skin). Intense α‐smooth muscle actin labeling in myofibroblasts was evident at 7 and 10 days. Vascular endothelial growth factor receptor‐2 and vascular endothelial growth factor‐A were detectable until 2 and 3 weeks, respectively, while transforming growth factor‐β1 protein was detectable in endothelial cells and myofibroblasts until 3–4 weeks and in the extracellular matrix for 16 weeks. Incisional wound granulation tissue largely developed within 3–7 days in the presence of hypoxia. Remodeling, marked by a decline in the percent vascular volume and increased cellular apoptosis, occurred largely in the absence of detectable hypoxia. The expression of vascular endothelial growth factor‐A, vascular endothelial growth factor receptor‐2, and transforming growth factor‐β1 is evident prior, during, and after the peak of vascular volume reflecting multiple roles for these factors during wound healing.

Hypoxic Conditioning Enhances the Angiogenic Paracrine Activity of Human Adipose-Derived Stem Cells

Human adipose-derived stem cells (ASCs) secrete cytokines and growth factors that can be harnessed in a paracrine fashion for promotion of angiogenesis, cell survival, and activation of endogenous stem cells. We recently showed that hypoxia is a powerful stimulus for an angiogenic activity from ASCs in vitro and here we investigate the biological significance of this paracrine activity in an in vivo angiogenesis model. A single in vitro exposure of ASCs to severe hypoxia (<0.1% O2) significantly increased both the transcriptional and translational level of the vascular endothelial growth factor-A (VEGF-A) and angiogenin (ANG). The angiogenicity of the ASC-conditioned medium (ASC(CM)) was assessed by implanting ASC(CM)-treated polyvinyl alcohol sponges subcutaneously for 2 weeks in mice. The morphometric analysis of anti-CD31-immunolabeled sponge sections demonstrated an increased angiogenesis with hypoxic ASC(CM) treatment compared to normoxic control ASC(CM) treatment (percentage vascular volume; 6.0%±0.5% in the hypoxic ASC(CM) vs. 4.1%±0.7% in the normoxic ASC(CM), P<0.05). Reduction of VEGF-A and ANG levels in the ASC(CM) with respective neutralizing antibodies before sponge implantation showed a significantly diminished angiogenic response (3.5%±0.5% in anti-VEGF-A treated, 3.2%±0.7% in anti-ANG treated, and 3.5%±0.6% in anti-VEGF-A/ANG treated). Further, both the normoxic and hypoxic ASC(CM) were able to sustain in vivo lymphangiogenesis in sponges. Collectively, the model demonstrated that the increased paracrine production of the VEGF-A and ANG in hypoxic-conditioned ASCs in vitro translated to an in vivo effect with a favorable biological significance. These results further illustrate the potential for utilization of an in vitro optimized ASC(CM) for in vivo angiogenesis-related applications as an effective cell-free technology.

Extracellular matrix of secondary lymphoid organs impacts on B-cell fate and survival

Significance We describe a unique extracellular matrix (ECM) niche in the spleen, the marginal zone (MZ), that supports a specialized population of MZ B lymphocytes that respond rapidly to blood-borne antigens and are therefore crucial for the first line of immune defense. We show, for the first time, that both the novel 3D structure and the biochemical composition of the ECM impacts on B-cell fate and survival. Similar pericellular ECM networks occur in thymus, bone marrow, and lymph node; hence, our data are likely to have broader ramifications to the fate and survival of other immune cells. We describe a unique extracellular matrix (ECM) niche in the spleen, the marginal zone (MZ), characterized by the basement membrane glycoproteins, laminin α5 and agrin, that promotes formation of a specialized population of MZ B lymphocytes that respond rapidly to blood-borne antigens. Mice with reduced laminin α5 expression show reduced MZ B cells and increased numbers of newly formed (NF) transitional B cells that migrate from the bone marrow, without changes in other immune or stromal cell compartments. Transient integrin α6β1-mediated interaction of NF B cells with laminin α5 in the MZ supports the MZ B-cell population, their long-term survival, and antibody response. Data suggest that the unique 3D structure and biochemical composition of the ECM of lymphoid organs impacts on immune cell fate.

Blue Rubber Bleb Nevus (BRBN) Syndrome Is Caused by Somatic TEK (TIE2) Mutations.

Blue rubber bleb nevus syndrome (Bean syndrome) is a rare, severe disorder of unknown cause, characterized by numerous cutaneous and internal venous malformations; gastrointestinal lesions are pathognomonic. We discovered somatic mutations in TEK, the gene encoding TIE2, in 15 of 17 individuals with blue rubber bleb nevus syndrome. Somatic mutations were also identified in five of six individuals with sporadically occurring multifocal venous malformations. In contrast to common unifocal venous malformation, which is most often caused by the somatic L914F TIE2 mutation, multifocal forms are predominantly caused by double (cis) mutations, that is, two somatic mutations on the same allele of the gene. Mutations are identical in all lesions from a given individual. T1105N-T1106P is recurrent in blue rubber bleb nevus, whereas Y897C-R915C is recurrent in sporadically occurring multifocal venous malformation: both cause ligand-independent activation of TIE2, and increase survival, invasion, and colony formation when expressed in human umbilical vein endothelial cells.