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Biomedical subjects

Jeffrey M Davidson

Publications and source records attributed to Jeffrey M Davidson.

At least 19 recordsLinked to original sources
PubMed2007

Development of improved nanoparticulate polyelectrolyte complex physicochemistry by nonstoichiometric mixing of polyions with similar molecular weights.

Water-based, biodegradable polyelectrolyte complex dispersions (PECs) prepared by mixing oppositely charged polyions are advantageous drug delivery systems due to constituent biocompatibility and nanoparticulate architectures. Reaction phase environmental parameters dictate PEC physicochemical properties, and specifically, complexation between polyelectrolytes having significantly different molecular weights leads to formation of water-insoluble aggregates. Starting with this fact, four-component similar and dissimilar molecular weight PEC chemistries were applied and compared with and without frequency-induced dispergation. The goal was to define nanoparticulate PEC systems with desirable characteristics for use in biological systems. Results show PEC formulations from precursors with similar low molecular weights yielded dispersions with suitable physicochemical characteristics, as verified by photon correlation spectroscopy and TEM, presumably due to efficient ion pairing. Similar low molecular weight PECs fabricated with dispergation exhibited pH-independent stability, as validated by charge and size measurements. These physicochemical advantages lead to an ideal delivery platform.

Biocompatible Materials↗
PubMed2007

Accelerated wound closure in mice deficient for interleukin-10.

The impact of the local inflammatory response on the process of wound healing has been debated for decades. In particular, the question whether infiltrating macrophages and granulocytes promote or impede tissue repair has received much attention. In the present study, we show that wound healing is accelerated in mice deficient for the anti-inflammatory cytokine interleukin (IL)-10. IL-10-/- mice closed excisional wounds significantly earlier compared with IL-10-competent control littermates. This effect was attributable to accelerated epithelialization as well as enhanced contraction of the wound tissue in the mutant animals. Increased alpha-smooth muscle actin expression in IL-10-deficient mice suggests that augmented myofibroblast differentiation is responsible for the enhanced contraction of wounds in mutant mice. The number of macrophages infiltrating the wound tissue was significantly increased in IL-10-/- mice compared with control littermates suggesting that this cell type mediates the accelerated tissue repair. These results show for the first time that IL-10 can impede wound repair.

Actins↗
PubMed2006

Wound healing in the alpha2beta1 integrin-deficient mouse: altered keratinocyte biology and dysregulated matrix metalloproteinase expression.

The alpha2beta1 integrin, a collagen/laminin receptor, is expressed at high level in the basal cell layer of the epidermis. To define the role of the alpha2beta1 integrin in wound healing, wound repair was extensively evaluated in wild-type and alpha2-null mice in vivo. In addition, the impact of alpha2beta1 integrin-deficiency on the function of primary murine keratinocytes in vitro was analyzed. Our in vivo findings demonstrate that genetic deletion of the alpha2beta1 integrin does not significantly alter the rate of re-epithelialization, collagen deposition, or tensile strength during wound closure in mice. In marked contrast to the observed similarities in wound healing, deletion of the alpha2beta1 integrin resulted in a dramatic increase in neoangiogenesis in the wound microenvironment. In contrast to in vivo studies, primary keratinocytes from alpha2-null mice adhered poorly and displayed impaired migration on type I collagen in vitro. We demonstrate that alpha2beta1 integrin-ligation negatively regulates expression of genes including matrix metalloproteinases both in vivo and in vitro. Furthermore, the changes in gene expression could potentially account for relatively normal wound healing in the alpha2-deficient mouse and our recent observation that suggests an antiangiogenic role for the alpha2beta1 integrin in vivo.

Animals↗
PubMed2006

Integrin alpha2beta1 is required for regulation of murine wound angiogenesis but is dispensable for reepithelialization.

The alpha2beta1 integrin functions as the major receptor for collagen type I on a large number of different cell types, including keratinocytes, fibroblasts, endothelial cells, and a variety of inflammatory cells. Recently, we demonstrated that adhesion of keratinocytes to collagen critically depends on alpha2beta1, whereas fibroblasts can partly compensate for loss of alpha2beta1 in simple adhesion to collagen. However, in three-dimensional collagen matrices, alpha2beta1-null fibroblasts are hampered in generating mechanical forces. These data suggested a pivotal role for alpha2beta1 during wound healing in vivo. Unexpectedly, reepithelialization of excisional wounds of alpha2beta1-null mice was not impaired, indicating that keratinocytes do not require adhesion to or migration on collagen for wound closure. Whereas wound contraction and myofibroblast differentiation were similar, wound tensile strain was reduced in alpha2beta1-null mice, suggesting subtle changes in organization of the extracellular matrix. In addition, we observed reduced influx of mast cells into the granulation tissue, whereas infiltration of other inflammatory cells was not impaired. Interestingly, ablation of alpha2beta1 resulted in strong enhancement of neovascularization of granulation tissue and sponge implants. Both ultrastructurally and functionally, these new blood vessels appeared intact. In conclusion, our data show unique and overlapping functions of alpha2beta1 integrin during murine cutaneous wound healing.

Animals↗
PubMed2006

Murine model of the Ehlers-Danlos syndrome. col5a1 haploinsufficiency disrupts collagen fibril assembly at multiple stages.

The most commonly identified mutations causing Ehlers-Danlos syndrome (EDS) classic type result in haploinsufficiency of proalpha1(V) chains of type V collagen, a quantitatively minor collagen that co-assembles with type I collagen as heterotypic fibrils. To determine the role(s) of type I/V collagen interactions in fibrillogenesis and elucidate the mechanism whereby half-reduction of type V collagen causes abnormal connective tissue biogenesis observed in EDS, we analyzed mice heterozygous for a targeted inactivating mutation in col5a1 that caused 50% reduction in col5a1 mRNA and collagen V. Comparable with EDS patients, they had decreased aortic stiffness and tensile strength and hyperextensible skin with decreased tensile strength of both normal and wounded skin. In dermis, 50% fewer fibrils were assembled with two subpopulations: relatively normal fibrils with periodic immunoreactivity for collagen V where type I/V interactions regulate nucleation of fibril assembly and abnormal fibrils, lacking collagen V, generated by unregulated sequestration of type I collagen. The presence of the aberrant fibril subpopulation disrupts the normal linear and lateral growth mediated by fibril fusion. Therefore, abnormal fibril nucleation and dysfunctional fibril growth with potential disruption of cell-directed fibril organization leads to the connective tissue dysfunction associated with EDS.

Alleles↗
PubMed2006

Healing slack skin.

A non-lethal, murine knockout of fibulin-5 with features of autosomal recessive cutis laxa and marked defects in elastic fiber formation amplifies previous observations on the minimal role of the elastic component in acute, cutaneous wound healing. More demanding wound models or long-term studies may yet reveal how fibulin-5 and elastin impact the quality of repair.

Animals↗
PubMed2006

Novel approaches for understanding the mechanisms of wound repair.

Mechanisms that drive wound repair are complex and have challenged wound-healing investigators for many years. In this review, we present four examples of new tools that are being utilized to discover events that drive wound repair and regeneration. Laser capture microdissection facilitates the focused collection of tissue for purposes of genomic or proteomic analysis from specific cell populations within the wound bed. Tissue profiling and protein imaging by matrix-assisted laser desorption ionization mass spectrometry are two proteomic-based tools that permit rapid analysis with spatial orientation and relative abundance of hundreds to thousands of molecules from intact tissues. Another approach uses an in vivo porcine model to harness a strategy of adenoviral-driven receptor overexpression. This biological model closely mimics the human setting and permits transient stimulation along a specific cytokine pathway to tip the balance in favor of accelerated repair. The advent of new approaches that collect cell samples from within their in vivo circumstance while preserving discrete cellular localizations is likely to move the field of wound repair forward.

Adenoviridae↗
PubMed2006

CARP: fishing for novel mechanisms of neovascularization.

Gene expression profiling of mouse skin wounds has led to the discovery of numerous target genes that may have therapeutic or diagnostic value. Among these, cardiac ankyrin repeat protein (CARP, ankrd1) expression was markedly and persistently elevated in several cutaneous compartments. This review summarizes the current state of knowledge of CARP and its regulation in biological systems. In addition to its role as a nuclear transcription cofactor in many cell types including vascular endothelium, CARP is also a structural component of the sarcomere. CARP transcripts are prominent in cardiogenesis and muscle injury, and they are under complex regulation by cytokines, hypoxia, doxorubicin, and other forms of stress. CARP overexpression in wounds by adenoviral gene transfer leads to a high vascular density, and CARP exerts effects on endothelial behavior. The unusual cellular distribution and actions of CARP make it a novel candidate gene in tissue repair.

Animals↗
PubMed2006

Plasmin modulates vascular endothelial growth factor-A-mediated angiogenesis during wound repair.

Plasmin-catalyzed cleavage of the vascular endothelial growth factor (VEGF)-A isoform VEGF165 results in loss of its carboxyl-terminal heparin-binding domain and significant loss in its bioactivity. Little is known about the in vivo significance of this process. To investigate the biological relevance of the protease sensitivity of VEGF165 in wound healing we assessed the activity of a VEGF165 mutant resistant to plasmin proteolysis (VEGF165(A111P)) in a genetic mouse model of impaired wound healing (db/db mouse). In the present study we demonstrate that in this mouse model plasmin activity is increased at the wound site. The stability of the mutant VEGF165 was substantially increased in wound tissue lysates in comparison to wild-type VEGF165, thus indicating a prolonged activity of the plasmin-resistant VEGF165 mutant. The db/db delayed healing phenotype could be reversed by topical application of wild-type VEGF165 or VEGF165(A111P). However, resistance of VEGF165 to plasmin cleavage resulted in the increased stability of vascular structures during the late phase of healing due to increased recruitment of perivascular cells and delayed and reduced endothelial cell apoptosis. Our data provide the first indication that plasmin-catalyzed cleavage regulates VEGF165-mediated angiogenesis in vivo. Inactivation of the plasmin cleavage site Arg110/Ala111 may preserve the biological function of VEGF165 in therapeutic angiogenesis under conditions in which proteases are highly active, such as wound repair and inflammation.

Animals↗
PubMed2005

Fibroblast differentiation of bone marrow-derived cells during wound repair.

To examine the ontogeny of the wound fibroblast, bone marrow transplantation was performed to wild-type recipients from transgenic donors that express both the luciferase and beta-galactosidase reporter genes under transcriptional control of the promoter/enhancer for the alpha2 chain of type I collagen. Polyvinyl alcohol sponges were implanted to elicit a naïve granulation tissue response, removed at defined time points, and processed for nucleic acids and histochemistry. Quantitative PCR for the luciferase transgene demonstrated that donor-derived cells were present during inflammation, declined, and rebounded during later stages of tissue remodeling. Furthermore, quantitative RT-PCR revealed that bone marrow-derived collagen transcripts contributed significantly to the total collagen I alpha2 promoter activation during later stages of repair. beta-galactosidase staining revealed that indeed those cells which expressed the transgene exhibited a fibroblastic phenotype, co-localized with sites of active collagen deposition, and expressed fibroblast specific protein-1. These data strongly support the concept that the adult bone marrow compartment houses progenitors with the potential to migrate to sites of tissue damage, and participate in repair beyond inflammation as fibroblasts. Moreover, that bone marrow-derived fibroblasts make a substantial contribution to the formation of new connective tissue, including type I collagen, during wound repair.

Animals↗
PubMed2005

CARP, a cardiac ankyrin repeat protein, is up-regulated during wound healing and induces angiogenesis in experimental granulation tissue.

Cardiac ankyrin repeat protein (CARP) was identified by subtractive hybridization as one of a group of genes that are rapidly modulated by acute wounding of mouse skin. Quantitative RT-PCR showed that CARP was strongly induced during the first day after wounding (157.1-fold), and the high level persisted for up to 14 days. Immunohistochemistry and in situ hybridization revealed that CARP was expressed in skeletal muscle, vessel wall, hair follicle, inflammatory cells, and epidermis in the wound area. To examine the effects of CARP on wound healing, we developed an adenoviral CARP vector to treat subcutaneously implanted sponges in either rats or Flk-1(LacZ) knock-in mice. Four days after infection, CARP-infected sponges in rats showed a remarkable increase in the vascular component in granulation tissue as compared to Ad-LacZ controls. This result was confirmed by CD34 immunostaining. By 7 days post-infection of sponge implants in Flk-1(LacZ) knock-in mice, granulation tissue showed many more LacZ-positive cells in Ad-CARP-infected sponges than in virus controls. Ad-CARP treatment also induced neovascularization and increased blood perfusion in rabbit excisional wounds in and ischemic rat wounds. These findings indicate that CARP could play a unique role in therapeutic angiogenesis during wound healing.

Angiogenic Proteins↗
PubMed2004

Gene transfer in tissue repair: status, challenges and future directions.

Wound repair involves a complex interaction of various cell types, extracellular matrix molecules and soluble mediators. Details on signals controlling wound cell activities are beginning to emerge. In recent years this knowledge has been applied to a number of therapeutic strategies in soft tissue repair. Key challenges include re-adjusting the adult repair process in order to augment diseased healing processes, and providing the basis for a regenerative rather than a reparative wound environment. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trials indicates that an important aspect of the growth factor wound-healing paradigm is the effective delivery of these polypeptides to the wound site. A molecular genetic approach in which genetically modified cells synthesise and deliver the desired growth factor in a time-regulated manner is a powerful means to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. This article summarises repair mechanisms and their failure, and gives an overview of techniques and studies applied to gene transfer in tissue repair. It also provides perspectives on potential targets for gene transfer technology.

Adenoviridae↗
PubMed2003

Transforming growth factor-beta-dependent and -independent pathways of induction of tubulointerstitial fibrosis in beta6(-/-) mice.

Transforming growth factor-beta1 (TGF-beta1) and the renin-angiotensin-aldosterone system are key mediators in kidney fibrosis. Integrin alphavbeta6, a heterodimeric matrix receptor expressed in epithelia, binds and activates latent TGF-beta1. We used beta6 integrin-null mice (beta6(-/-)) to determine the role of local TGF-beta1 activation in renal fibrosis in the unilateral ureteral obstruction (UUO) model. Obstructed kidneys from beta6(-/-) mice showed less injury than obstructed kidneys from wild-type (WT) mice, associated with lower collagen I, collagen III, plasminogen activator inhibitor (PAI-1), and TGF-beta1 mRNA levels and lower collagen content. Infusion with either angiotensin II (Ang II) or aldosterone (Aldo) or combination in beta6(-/-) UUO mice significantly increased collagen contents to levels comparable to those in identically treated WT. Active TGF-beta protein expression in beta6(-/-) mice was less in UUO kidneys with or without Ang II infusion compared to matched WT mice. Activated Smad 2 levels in beta6(-/-) obstructed kidneys were lower than in WT UUO mice, and did not increase when fibrosis was induced in beta6(-/-) UUO mice by Ang II infusion. Anti-TGF-beta antibody only partially decreased this Ang II-stimulated fibrosis in beta6(-/-) UUO kidneys. In situ hybridization and immunostaining showed low expression of PAI-1 mRNA and protein in tubular epithelium in beta6(-/-) UUO kidneys, with increased PAI-1 expression in response to Ang II, Aldo, or both. Our results indicate that interruption of alphavbeta6-mediated activation of TGF-beta1 can protect against tubulointerstitial fibrosis. Further, the robust induction of tubulointerstitial fibrosis without increase in activated Smad 2 levels in obstructed beta6(-/-) mice by Ang II suggests the existence of a TGF-beta1-independent pathway of induction of fibrosis through angiotensin.

Aldosterone↗
PubMed2003

The biomechanical response to doses of TGF-beta 2 in the healing rabbit medial collateral ligament.

Ligament injuries result in significant disability in over 100,000 patients each year. Despite current methods of treatment, 13% of patients with medial collateral ligament (MCL) injury develop early signs of arthritis, suggesting an incomplete return of knee stability. The principal hypothesis of this work was that the addition of TGF-beta 2 to the healing MCL would accelerate the development of scar strength and stiffness. Forty-four rabbits were divided evenly into four groups, with each group receiving either 0.1, 1 or 5 microg of TGF-beta 2 and the fourth group receiving 1 microg TGF-beta 2 and 1 microg of PDGF. Each rabbit underwent bilateral transection of the MCL, with one side having treatment with one of four doses of growth factor and the other side left untreated. All animals were sacrificed at 6 weeks and the structural properties of maximum load at failure, stiffness, and energy absorbed at failure measured. All treatment groups demonstrated an increase in scar mass, but no group had a significant increase in scar load at failure at 6 weeks. The addition of 0.1 microg TGF-beta 2 led to a significant increase in scar stiffness. The addition of PDGF had no significant effect on any of the parameters studied. This study suggests the mechanical stiffness, but not the load at failure, of ligament scar can be significantly altered by the administration of TGF-beta 2.

Animals↗
PubMed2003

SPARC-null mice display abnormalities in the dermis characterized by decreased collagen fibril diameter and reduced tensile strength.

Although collagen and elastic fibers are among the major structural constituents responsible for the mechanical properties of skin, proteins that associate with these components are also important for directing formation and maintaining the stability of these fibers. We present evidence that SPARC (secreted protein acidic and rich in cysteine) contributes to collagen fibril formation in the dermis. The skin of SPARC-null adult mice had approximately half the tensile strength as that of wild-type skin. Moreover, the collagen content of SPARC-null skin, as measured by hydroxyproline analysis, was substantially reduced in adult mice. At 2 weeks of age, no differences in collagen content were observed; within 2 months, however, the dermis of SPARC-null mice displayed a reduced collagen content that persisted through adulthood until approximately 20 months, when collagen levels of SPARC-null skin approximated those of wild-type controls. The collagen fibrils present in SPARC-null skin were smaller and more uniform in diameter, in comparison with those of wild-type skin. At 5 months of age, the average fibril diameter in SPARC-null versus wild-type skin was 60.2 nm versus 87.9 nm, respectively. Extraction of soluble dermal collagen revealed a relative increase in collagen VI, accompanied by a decrease in collagen I, in SPARC-null mice. A reduction in the relative amounts of higher-molecular weight collagen complexes was also observed in extracts of dermis from SPARC-null animals. Thus the absence of SPARC compromises the mechanical properties of the dermis, an effect that we attribute, at least in part, to the changes in the structure and composition of its collagenous extracellular matrix.

Acetic Acid↗
PubMed2003

Comparison of mouse matrix metalloproteinase 13 expression in free-electron laser and scalpel incisions during wound healing.

Collagenase-3 (matrix metalloproteinase 13, MMP-13) was employed as a surrogate marker to compare the characteristics of incisional wound repair after surgery with the free-electron laser at 6.1 microm and the scalpel. Using a transgenic mouse strain with the MMP-13 or the COL1A2 promoter driving luciferase expression, we observed MMP-13 and COL1A2 expression, tensile strength, macrophage infiltration, and wound histology for up to 62 d. The scalpel incisions showed higher tensile strength than free-electron laser wounds from days 10 to 22 postwounding, despite minimal collateral thermal damage. After 45 d healing was similar. Trichrome staining confirmed that the scalpel incisions had more dense collagen deposition than free-electron laser incisions up to 36 d postinjury, but at day 45 they became similar. MMP-13 expression was biphasic, with peak activities at days 15 and 37 after injury, whereas free-electron laser wounds showed greater luciferase activity than scalpel wounds. Peak COL1A2 activity preceded the MMP-13 maximum. MMP-13 expression localized predominantly to dermal fibroblasts near the epidermis at day 15, and in the region of the deep dermis, muscle, and fascia at day 37 postwounding. Migrating muscle cells, but not all skeletal muscle cells, also expressed MMP-13. Free-electron laser incisions contained more macrophages than scalpel wounds at days 2 and 7 postinjury, suggesting that free-electron laser irradiation exacerbated the inflammatory response and thereby stimulated MMP-13 expression. These results revealed that MMP-13 was involved in a series of coordinated events during wound healing, not only the long-term remodeling of wound connective tissue, but also skeletal muscle repair. MMP-13 activity in vivo may correlate with the extent of tissue damage.

Animals↗