Jeffrey M. Davidson

Altered wound healing in mice lacking a functional osteopontin gene (spp1).

Osteopontin (OPN) is an arginine-glycine-aspartate (RGD)- containing glycoprotein encoded by the gene secreted phosphoprotein 1 (spp1). spp1 is expressed during embryogenesis, wound healing, and tumorigenesis; however, its in vivo functions are not well understood. Therefore, OPN null mutant mice were generated by targeted mutagenesis in embryonic stem cells. In OPN mutant mice, embryogenesis occurred normally, and mice were fertile. Since OPN shares receptors with vitronectin (VN), we tested for compensation by creating mice lacking both OPN and VN. The double mutants were also viable, suggesting that other RGD-containing ligands replace the embryonic loss of both proteins. We tested the healing of OPN mutants after skin incisions, where spp1 was upregulated as early as 6 h after wounding. Although the tensile properties of the wounds were unchanged, ultrastructural analysis showed a significantly decreased level of debridement, greater disorganization of matrix, and an alteration of collagen fibrillogenesis leading to small diameter collagen fibrils in the OPN mutant mice. These data indicate a role for OPN in tissue remodeling in vivo, and suggest physiological functions during matrix reorganization after injury.

Recombinant basic fibroblast growth factor accelerates wound healing

Basic fibroblast growth factor (bFGF) stimulates extracellular matrix metabolism, growth, and movement of mesodermally derived cells. We have previously shown that collagen content in polyvinyl alcohol sponges increased after bFGF treatment. We hypothesized that bFGF-treated incisional wounds would heal more rapidly. After intraperitoneal pentobarbital anesthesia, male, 200- to 250-g, Sprague-Dawley rats (n = 27) each underwent two sets of paired, transverse, dorsal incisions closed with steel sutures. On Day 3 postwounding, 0.4 ml of bFGF (recombinant, 400 ng. Synergen) or normal saline was injected into one of each paired incisions. Animals were killed with ether on postwounding Days 5, 6, and 7 and their dorsal pelts were excised. Fresh or formalin-fixed wound strips were subjected to tensile strength measurements using a tensiometer. Breaking energy was calculated. Wound collagen content (hydroxyproline) was measured in wound-edge samples following hydrolysis using high-performance liquid chromatography. There was an overall significant increase in fresh wound tensile strength (13.7 +/- 1.06 vs 19.1 +/- 1.99 g/mm, P less than 0.01) and wound breaking energy (476 +/- 47 vs 747 +/- 76 mm2, P less than 0.001) in bFGF-treated incisions. There was an increase in wound collagen content which was not statistically significant and there was no difference in fixed incisional tensile strength. Histologic examination showed better organization and maturation in bFGF wounds. Recombinant bFGF accelerates normal rat wound healing. This may be due to earlier accumulation of collagen and fibroblasts and/or to greater collagen crosslinking in bFGF-treated wounds.

Dynamic reciprocity in the wound microenvironment.

Here, we define dynamic reciprocity (DR) as an ongoing, bidirectional interaction among cells and their surrounding microenvironment. In this review, we posit that DR is especially meaningful during wound healing as the DR‐driven biochemical, biophysical, and cellular responses to injury play pivotal roles in regulating tissue regenerative responses. Such cell–extracellular matrix interactions not only guide and regulate cellular morphology, but also cellular differentiation, migration, proliferation, and survival during tissue development, including, e.g., embryogenesis, angiogenesis, as well as during pathologic processes including cancer, diabetes, hypertension, and chronic wound healing. Herein, we examine DR within the wound microenvironment while considering specific examples across acute and chronic wound healing. This review also considers how a number of hypotheses that attempt to explain chronic wound pathophysiology may be understood within the DR framework. The implications of applying the principles of DR to optimize wound care practice and future development of innovative wound healing therapeutics are also briefly considered.

Animal models for wound repair.

Abstract Progress in wound pharmacology is dependent on the availability of suitable animal wound models. All animal models try to reflect human wound healing problems. In acute models it is easier to achieve approximations to the clinical situation than in models for the chronic wound.

Transforming Growth Factor-β-Dependent and -Independent Pathways of Induction of Tubulointerstitial Fibrosis in β6−/− Mice

Transforming growth factor-β1 (TGF-β1) and the renin-angiotensin-aldosterone system are key mediators in kidney fibrosis. Integrin αvβ6, a heterodimeric matrix receptor expressed in epithelia, binds and activates latent TGF-β1. We used β6 integrin-null mice (β6−/−) to determine the role of local TGF-β1 activation in renal fibrosis in the unilateral ureteral obstruction (UUO) model. Obstructed kidneys from β6−/− 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-β1 mRNA levels and lower collagen content. Infusion with either angiotensin II (Ang II) or aldosterone (Aldo) or combination in β6−/− UUO mice significantly increased collagen contents to levels comparable to those in identically treated WT. Active TGF-β protein expression in β6−/− mice was less in UUO kidneys with or without Ang II infusion compared to matched WT mice. Activated Smad 2 levels in β6−/− obstructed kidneys were lower than in WT UUO mice, and did not increase when fibrosis was induced in β6−/− UUO mice by Ang II infusion. Anti-TGF-β antibody only partially decreased this Ang II-stimulated fibrosis in β6−/− UUO kidneys. In situ hybridization and immunostaining showed low expression of PAI-1 mRNA and protein in tubular epithelium in β6−/− UUO kidneys, with increased PAI-1 expression in response to Ang II, Aldo, or both. Our results indicate that interruption of αvβ6-mediated activation of TGF-β1 can protect against tubulointerstitial fibrosis. Further, the robust induction of tubulointerstitial fibrosis without increase in activated Smad 2 levels in obstructed β6−/− mice by Ang II suggests the existence of a TGF-β1-independent pathway of induction of fibrosis through angiotensin.

Adhesion formation is reduced after laparoscopic surgery

AbstractBackground: Adhesion formation after abdominal operations causes significant morbidity. Methods: Adhesion formation in pigs was compared after placement of prosthetic mesh during celiotomy (group 1), laparoscopy with large incision (group 2), and laparoscopy (group 3). After peritoneum was excised, polypropylene mesh was fixed to the abdominal wall, then to the opposite abdominal wall in the preperitoneal space followed by peritoneal closure. Adhesion area, grade, and vascularity were measured. Results: More adhesions (p < 0.02) covered intraperitoneal mesh (7.57 ± 1.89 cm2) than covered reperitonealized mesh (2.16 ± 1.13 cm2), and adhesion grade was significantly greater (p < 0.02). Adhesion areas were significantly greater in groups 1 and 2 than in group 3 (p= 0.001 and 0.03, respectively). Adhesion grade was significantly greater in groups 1 and 2 than in group 3 (p= 0.02 and p= 0.04, respectively). Groups 1 and 2 had more vascular adhesions than group 3 (p < 0.01 and p= 0.02, respectively) Conclusions: A foreign body within the peritoneum stimulates more numerous and denser adhesions. Tissue trauma distant from the site of adhesions increases their formation. A major advantage of laparoscopic surgery is decreased adhesion formation.

The Wnt modulator sFRP2 enhances mesenchymal stem cell engraftment, granulation tissue formation and myocardial repair.

Cell-based therapies, using multipotent mesenchymal stem cells (MSCs) for organ regeneration, are being pursued for cardiac disease, orthopedic injuries and biomaterial fabrication. The molecular pathways that regulate MSC-mediated regeneration or enhance their therapeutic efficacy are, however, poorly understood. We compared MSCs isolated from MRL/MpJ mice, known to demonstrate enhanced regenerative capacity, to those from C57BL/6 (WT) mice. Compared with WT-MSCs, MRL-MSCs demonstrated increased proliferation, in vivo engraftment, experimental granulation tissue reconstitution, and tissue vascularity in a murine model of repair stimulation. The MRL-MSCs also reduced infarct size and improved function in a murine myocardial infarct model compared with WT-MSCs. Genomic and functional analysis indicated a downregulation of the canonical Wnt pathway in MRL-MSCs characterized by significant up-regulation of specific secreted frizzled-related proteins (sFRPs). Specific knockdown of sFRP2 by shRNA in MRL-MSCs decreased their proliferation and their engraftment in and the vascular density of MRL-MSC-generated experimental granulation tissue. These results led us to generate WT-MSCs overexpressing sFRP2 (sFRP2-MSCs) by retroviral transduction. sFRP2-MSCs maintained their ability for multilineage differentiation in vitro and, when implanted in vivo, recapitulated the MRL phenotype. Peri-infarct intramyocardial injection of sFRP2-MSCs resulted in enhanced engraftment, vascular density, reduced infarct size, and increased cardiac function after myocardial injury in mice. These findings implicate sFRP2 as a key molecule for the biogenesis of a superior regenerative phenotype in MSCs.

CUTIS LAXA ARISING FROM FRAMESHIFT MUTATIONS IN EXON 30 OF THE ELASTIN GENE (ELN)

Congenital cutis laxa, a rare syndrome with marked skin laxity and pulmonary and cardiovascular compromise, is due to defective elastic fiber formation. In several cases, skin fibroblast tropoelastin production is markedly reduced yet reversed in vitro by transforming growth factor-β treatment. We previously showed that this reversal was due to elastin mRNA stabilization in one cell strain, and here this behavior was confirmed in skin fibroblasts from two generations of a second family. cDNA sequencing and heteroduplex analysis of elastin gene transcripts from three fibroblast strains in two kindreds now identify two frameshift mutations (2012ΔG and 2039ΔC) in elastin gene exon 30, thus leading to missense C termini. No other mutations were present in theELN cDNA sequences of all three affected individuals. Transcripts from both alleles in each kindred were unstable and responsive to transforming growth factor-β. Exons 22, 23, 26A, and 32 were always absent. Since exon 30 underwent alternative splicing in fibroblasts, we speculate that a differential splicing pattern could conceivably lead to phenotypic rescue. These two dominant-acting, apparently de novo mutations in the elastin gene appear to be responsible for qualitative and quantitative defects in elastin, resulting in the cutis laxa phenotype.

Absence of angiotensin II type 1 receptor in bone marrow–derived cells is detrimental in the evolution of renal fibrosis

We examined the in vivo function of the angiotensin II type 1 receptor (Agtr1) on macrophages in renal fibrosis. Fourteen days after the induction of unilateral ureteral obstruction (UUO), wild-type mice reconstituted with marrow lacking the Agtr1 gene (Agtr1(-/-)) developed more severe interstitial fibrosis with fewer interstitial macrophages than those in mice reconstituted with Agtr1(+/+) marrow. These differences were not observed at day 5 of UUO. The expression of profibrotic genes - including TGF-beta1, alpha1(I) collagen, and alpha1(III) collagen - was substantially higher in the obstructed kidneys of mice with Agtr1(-/-) marrow than in those with Agtr1(+/+) marrow at day 14 but not at day 5 of UUO. Mice with Agtr1(-/-) marrow were characterized by reduced numbers of peripheral-blood monocytes and macrophage progenitors in bone marrow. In vivo assays revealed a significantly impaired phagocytic capability in Agtr1(-/-) macrophages. In vivo treatment of Agtr1(+/+) mice with losartan reduced phagocytic capability of Agtr1(+/+) macrophages to a level comparable to that of Agtr1(-/-) macrophages. Thus, during urinary tract obstruction, the Agtr1 on bone marrow-derived macrophages functions to preserve the renal parenchymal architecture, and this function depends in part on its modulatory effect on phagocytosis.

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 proα1(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.