Murphy Roths Large Research Articles

The super-healing MRL strain promotes muscle growth in muscular dystrophy through a regenerative extracellular matrix.

The Murphy Roths Large (MRL) mouse strain has "super-healing" properties that enhance recovery from injury. In mice, the DBA/2J strain intensifies many aspects of muscular dystrophy, so we evaluated the ability of the MRL strain to suppress muscular dystrophy in the Sgcg-null mouse model of limb girdle muscular dystrophy. A comparative analysis of Sgcg-null mice in the DBA/2J versus MRL strains showed greater myofiber regeneration, with reduced structural degradation of muscle in the MRL strain. Transcriptomic profiling of dystrophic muscle indicated strain-dependent expression of extracellular matrix (ECM) and TGF-β signaling genes. To investigate the MRL ECM, cellular components were removed from dystrophic muscle sections to generate decellularized myoscaffolds. Decellularized myoscaffolds from dystrophic mice in the protective MRL strain had significantly less deposition of collagen and matrix-bound TGF-β1 and TGF-β3 throughout the matrix. Dystrophic myoscaffolds from the MRL background, but not the DBA/2J background, were enriched in myokines like IGF-1 and IL-6. C2C12 myoblasts seeded onto decellularized matrices from Sgcg-/- MRL and Sgcg-/- DBA/2J muscles showed the MRL background induced greater myoblast differentiation compared with dystrophic DBA/2J myoscaffolds. Thus, the MRL background imparts its effect through a highly regenerative ECM, which is active even in muscular dystrophy.

OA susceptibility in mice is partially mediated by the gut microbiome, is transferrable via microbiome transplantation and is associated with immunophenotype changes

ObjectivesThe Murphy Roths Large (MRL)/MpJ ‘superhealer’ mouse strain is protected from post-traumatic osteoarthritis (OA), although no studies have evaluated the microbiome in the context of this protection. This study characterised...

Allele-specific expression reveals genetic drivers of tissue regeneration in mice.

In adult mammals, skin wounds typically heal by scarring rather than through regeneration. In contrast, "super-healer" Murphy Roths Large (MRL) mice have the unusual ability to regenerate ear punch wounds; however, the molecular basis for this regeneration remains elusive. Here, in hybrid crosses between MRL and non-regenerating mice, we used allele-specific gene expression to identify cis-regulatory variation associated with ear regeneration. Analyzing three major cell populations (immune, fibroblast, and endothelial), we found that genes with cis-regulatory differences specifically in fibroblasts were associated with wound-healing pathways and also co-localized with quantitative trait loci for ear wound-healing. Ectopic treatment with one of these proteins, complement factor H (CFH), accelerated wound repair and induced regeneration in typically fibrotic wounds. Through single-cell RNA sequencing (RNA-seq), we observed that CFH treatment dramatically reduced immune cell recruitment to wounds, suggesting a potential mechanism for CFH's effect. Overall, our results provide insights into the molecular drivers of regeneration with potential clinical implications.

Altered TGFB1 regulated pathways promote accelerated tendon healing in the superhealer MRL/MpJ mouse

To better understand the molecular mechanisms of tendon healing, we investigated the Murphy Roth’s Large (MRL) mouse, which is considered a model of mammalian tissue regeneration. We show that compared to C57Bl/6J (C57) mice, injured MRL tendons have reduced fibrotic adhesions and cellular proliferation, with accelerated improvements in biomechanical properties. RNA-seq analysis revealed that differentially expressed genes in the C57 healing tendon at 7 days post injury were functionally linked to fibrosis, immune system signaling and extracellular matrix (ECM) organization, while the differentially expressed genes in the MRL injured tendon were dominated by cell cycle pathways. These gene expression changes were associated with increased α-SMA+ myofibroblast and F4/80+ macrophage activation and abundant BCL-2 expression in the C57 injured tendons. Transcriptional analysis of upstream regulators using Ingenuity Pathway Analysis showed positive enrichment of TGFB1 in both C57 and MRL healing tendons, but with different downstream transcriptional effects. MRL tendons exhibited of cell cycle regulatory genes, with negative enrichment of the cell senescence-related regulators, compared to the positively-enriched inflammatory and fibrotic (ECM organization) pathways in the C57 tendons. Serum cytokine analysis revealed decreased levels of circulating senescence-associated circulatory proteins in response to injury in the MRL mice compared to the C57 mice. These data collectively demonstrate altered TGFB1 regulated inflammatory, fibrosis, and cell cycle pathways in flexor tendon repair in MRL mice, and could give cues to improved tendon healing.

Pyrroline-5-Carboxylate Reductase 1 Directs the Cartilage Protective and Regenerative Potential of Murphy Roths Large Mouse Mesenchymal Stem Cells.

Murphy Roths Large (MRL) mice possess outstanding capacity to regenerate several tissues. In the present study, we investigated whether this regenerative potential could be associated with the intrinsic particularities possessed by their mesenchymal stem cells (MSCs). We demonstrated that MSCs derived from MRL mice (MRL MSCs) display a superior chondrogenic potential than do C57BL/6 MSC (BL6 MSCs). This higher chondrogenic potential of MRL MSCs was associated with a higher expression level of pyrroline-5-carboxylate reductase 1 (PYCR1), an enzyme that catalyzes the biosynthesis of proline, in MRL MSCs compared with BL6 MSCs. The knockdown of PYCR1 in MRL MSCs, using a specific small interfering RNA (siRNA), abolishes their chondrogenic potential. Moreover, we showed that PYCR1 silencing in MRL MSCs induced a metabolic switch from glycolysis to oxidative phosphorylation. In two in vitro chondrocyte models that reproduce the main features of osteoarthritis (OA) chondrocytes including a downregulation of chondrocyte markers, a significant decrease of PYCR1 was observed. A downregulation of chondrocyte markers was also observed by silencing PYCR1 in freshly isolated healthy chondrocytes. Regarding MSC chondroprotective properties on chondrocytes with OA features, we showed that MSCs silenced for PYCR1 failed to protect chondrocytes from a reduced expression of anabolic markers, while MSCs overexpressing PYCR1 exhibited an increased chondroprotective potential. Finally, using the ear punch model, we demonstrated that MRL MSCs induced a regenerative response in non-regenerating BL6 mice, while BL6 and MRL MSCs deficient for PYCR1 did not. In conclusion, our results provide evidence that MRL mouse regenerative potential is, in part, attributed to its MSCs that exhibit higher PYCR1-dependent glycolytic potential, differentiation capacities, chondroprotective abilities, and regenerative potential than BL6 MSCs.

MANF Produced by MRL Mouse-Derived Mesenchymal Stem Cells Is Pro-regenerative and Protects From Osteoarthritis.

The super healer Murphy Roths Large (MRL) mouse represents the “holy grail” of mammalian regenerative model to decipher the key mechanisms that underlies regeneration in mammals. At a time when mesenchymal stem cell (MSC)-based therapy represents the most promising approach to treat degenerative diseases such as osteoarthritis (OA), identification of key factors responsible for the regenerative potential of MSC derived from MRL mouse would be a major step forward for regenerative medicine. In the present study, we assessed and compared MSC derived from MRL (MRL MSC) and C57BL/6 (BL6 MSC) mice. First, we compare the phenotype and the differentiation potential of MRL and BL6 MSC and did not observe any difference. Then, we evaluated the proliferation and migration potential of the cells and found that while MRL MSC proliferate at a slower rate than BL6 MSC, they migrate at a significantly higher rate. This higher migration potential is mediated, in part, by MRL MSC-secreted products since MRL MSC conditioned medium that contains a complex of released factors significantly increased the migration potential of BL6 MSC. A comparative analysis of the secretome by quantitative shotgun proteomics and Western blotting revealed that MRL MSC produce and release higher levels of mesencephalic astrocyte-derived neurotrophic factor (MANF) as compared to MSC derived from BL6, BALB/c, and DBA1 mice. MANF knockdown in MRL MSC using a specific small interfering RNA (siRNA) reduced both MRL MSC migration potential in scratch wound assay and their regenerative potential in the ear punch model in BL6 mice. Finally, injection of MRL MSC silenced for MANF did not protect mice from OA development. In conclusion, our results evidence that the enhanced regenerative potential and protection from OA of MRL mice might be, in part, attributed to their MSC, an effective reservoir of MANF.

The MRL/MpJ Mouse Strain Is Not Protected From Muscle Atrophy and Weakness After Rotator Cuff Tear.

Chronic rotator cuff tears are a common source of shoulder pain and disability. Patients with rotator cuff tears often have substantial weakness, fibrosis, and fat accumulation, which limit successful surgical repair and postoperative rehabilitation. The Murphy Roths Large (MRL) strain of mice have demonstrated superior healing and protection against pathological changes in several disease and injury conditions. We tested the hypothesis that, compared with the commonly used C57Bl/6 (B6) strain, MRL mice would have less muscle fiber atrophy and fat accumulation, and be protected against the loss in force production that occurs after cuff tear. Adult male B6 and MRL mice were subjected to a rotator cuff tear, and changes in muscle fiber contractility and histology were measured. RNA sequencing and shotgun metabolomics and lipidomics were also performed. The muscles were harvested one month after tear. B6 and MRL mice had a 40% reduction in relative muscle force production after rotator cuff tear. RNA sequencing identified an increase in fibrosis-associated genes and a reduction in mitochondrial metabolism genes. The markers of glycolytic metabolism increased in B6 mice, while MRL mice appeared to increase amino acid metabolism after tear. There was an accumulation of lipid after injury, although there was a divergent response between B6 and MRL mice in the types of lipid species that accrued. There were strain-specific differences between the transcriptome, metabolome, and lipidome of B6 and MRL mice, but these differences did not protect MRL mice from weakness and pathological changes after rotator cuff tear. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:811-822, 2020.

Comparative regenerative properties of mesenchymal stem cells isolated from MRL (Murphy Roths Large) versus C57Bl6 mice

Adult Mammals are unable to regenerate their injuried myocardium by contrast to Zebrafish or MRL mice. While myocardial repair has been shown after cryoinjury in MRL mice, it failed after coronary ligation leading to ischemic injury. This underlies the impact of the inflammatory environment on the intrinsic regenerative potential of MRL stem cells. Mesenchymal stem cells (MSC) administered as cardiac therapy have emerged as breakthrough immunomodulative and cytoprotective treatments for myocardial infarction. to compare the intrinsic regenerative properties of MSC derived from C57BL/6 (MSC-BL6) and MRL (MSC-MRL) mice in an ex vivo myocardial ischemia-reperfusion (IR) injury model and decipher the underlying mechanisms. FACS analysis allowed characteristic phenotyping of MSC isolated from C57BL/6 (MSC-B6) or MRL (MSC-MRL) murine bone marrow. Their differentiation potential into chondrocytes, osteoblasts and adipocytes upon inductive conditions was studied. Their migration capacities were evaluated using the in vitro scratch wound healing assay. Infarct size was measured in mouse hearts subjected to ex vivo 30 min-ischemia and 1 hour-reperfusion and treated by MSCs. In vitro, MSC-MRL showed a significantly higher migration potential than MSC-B6 in accordance with reduced expression levels of E-cadherin and cadherin 11 adhesion molecules. Using MRL-MSC conditioned medium, we demonstrated an increased migration capacity of MSC-B6 suggesting that the MRL-MSC release a soluble factor responsible for their potent homing potential to the wound site. Injected during reperfusion, MSC-MRL were able to protect the injured myocardium more efficiently than MSC-B6 in the ex vivo IR model (MSC-MRL: 47.18 ± 0.66%, n = 3 vs MSC-B6: 56.36 ± 3.17%, n = 3). MSC-MRL have superior cardioprotective effects for the treatment of IR injury compared to MSC-B6 probably due to higher migration capacities and specific regenerative secretome.

Assessing Autophagy in Mouse Models and Patients with Systemic Autoimmune Diseases.

Autophagy is a tightly regulated mechanism that allows cells to renew themselves through the lysosomal degradation of proteins, which are misfolded or produced in excess, and of damaged organelles. In the context of immunity, recent research has specially attempted to clarify its roles in infection, inflammation and autoimmunity. Autophagy has emerged as a spotlight in several molecular pathways and trafficking events that participate to innate and adaptive immunity. Deregulation of autophagy has been associated to several autoimmune diseases, in particular to systemic lupus erythematosus. Nowadays, however, experimental data on the implication of autophagy in animal models of autoimmunity or patients remain limited. In our investigations, we use Murphy Roths Large (MRL)/lymphoproliferation (lpr) lupus-prone mice as a mouse model for lupus and secondary Sjögren’s syndrome, and, herein, we describe methods applied routinely to analyze different autophagic pathways in different lymphoid organs and tissues (spleen, lymph nodes, salivary glands). We also depict some techniques used to analyze autophagy in lupus patient’s blood samples. These methods can be adapted to the analysis of autophagy in other mouse models of autoinflammatory diseases. The understanding of autophagy implication in autoimmune diseases could prove to be very useful for developing novel immunomodulatory strategies. Our attention should be focused on the fact that autophagy processes are interconnected and that distinct pathways can be independently hyper-activated or downregulated in distinct organs and tissues of the same individual.

In vivo anti-inflammatory activities of novel cytokine IL-38 in Murphy Roths Large (MRL)/lpr mice

The newly named interleukin (IL)-36 subfamily member IL-38 has been shown to exert anti-inflammatory activity. However, the in vivo immunomodulatory activity of IL-38 was poorly investigated in systemic lupus erythematosus (SLE). We have investigated the expression of CD4+IL-17+ Th17, CD4+IFN-γ+ Th1 and CD3+CD4−CD8− double negative (DN) T cells and the related immunopathological mechanisms in female MRL/lpr mice model of spontaneous lupus-like disease, with or without IL-38 treatment. Intravenous administration of murine recombinant IL-38 into MRL/lpr mice can ameliorate the lupus-like clinical symptoms including proteinuria, leukocyteuria and skin lesions. A remission of histopathology characteristics of skin and nephritis was also observed upon IL-38 treatment. Accordingly, IL-38 receptor was expressed on the cell surface of both CD4+ Th and CD19+ B lymphocytes. The splenic Th17 and DN T lymphocytes, the average mRNA level of epigenetically regulated gene expression of Th17 cells, and serum concentrations of IL-17 and IL-22 were significantly decreased upon the treatment of IL-38 (all p<0.05). The in vivo results suggest that IL-38 can ameliorate skin inflammation and nephritis in SLE mice probably via suppressing the formation of inflammatory cytokines such as IL-17 and IL-22, and pathogenic DN T cells. These findings may provide a biochemical basis for further investigation of the therapeutic mechanisms of IL-38 for the treatment of autoimmune-mediated inflammation.

Successful metabolic adaptations leading to the prevention of high fat diet-induced murine cardiac remodeling.

BackgroundCardiomyopathy is a devastating complication of obesity and type 2 diabetes mellitus (T2DM). It arises even in patients with normoglycemia (glycosylated hemoglobin, A1C ≤7 %). As obesity and T2DM are approaching epidemic levels worldwide, the cardiomyopathy associated with these diseases must be therapeutically addressed. We have recently analyzed the systemic effects of a 12-week high fat diet (HFD) on wild type mice from the C57Bl/6 (B6) strain and the wild type super-healing Murphy Roths Large (MRL) mouse strain. The MRL HFD mice gained significantly more weight than their control diet counterparts, but did not present any of the other usual systemic T2DM phenotypes.MethodsCardiac pathology and adaptation to HFD-induced obesity in the MRL mouse strain compared to the HFD C57Bl/6 mice were thoroughly analyzed with echocardiography, histology, qPCR, electron microscopy and immunoblots.ResultsThe obese HFD C57Bl/6 mice develop cardiac hypertrophy, cardiomyocyte lipid droplets, and initiate an ineffective metabolic adaptation of an overall increase in electron transport chain complexes. In contrast, the obese HFD MRL hearts do not display hypertrophy nor lipid droplets and their metabolism adapts quite robustly by decreasing pAMPK levels, decreasing proteins in the carbohydrate metabolism pathway and increasing proteins utilized in the β-oxidation pathway. The result of these metabolic shifts is the reduction of toxic lipid deposits and reactive oxygen species in the hearts of the obese HFD fed MRL hearts.ConclusionsWe have identified changes in metabolic signaling in obese HFD fed MRL mice that confer resistance to diabetic cardiomyopathy. The changes include a reduction of cardiac pAMPK, Glut4 and hexokinase2 in the MRL HFD hearts. Overall the MRL hearts down regulate glucose metabolism and favor lipid metabolism. These adaptations are essential to pursue for the identification of novel therapeutic targets to combat obesity related cardiomyopathy.

Remission of systemic lupus erythematosus disease activity with regulatory cytokine interleukin (IL)-35 in Murphy Roths Large (MRL)/lpr mice.

The immunological mechanisms mediated by regulatory cytokine interleukin (IL)-35 are unclear in systemic lupus erythematosus (SLE). We investigated the frequency of CD4(+) CD25(+) forkhead box protein 3 (FoxP3)(+) regulatory T (Treg ) and IL-10(+) regulatory B (Breg ) cells and related immunoregulatory mechanisms in a female Murphy Roths Large (MRL)/lpr mouse model of spontaneous lupus-like disease, with or without IL-35 treatment. A remission of histopathology characteristics of lupus flare and nephritis was observed in the MRL/lpr mice upon IL-35 treatment. Accordingly, IL-35 and IL-35 receptor subunits (gp130 and IL-12Rβ2) and cytokines of MRL/lpr and BALB/c mice (normal controls) were measured. The increased anti-inflammatory cytokines and decreased proinflammatory cytokines were possibly associated with the restoration of Treg and Breg frequency in MRL/lpr mice with IL-35 treatment, compared to phosphate-buffered saline (PBS) treatment. mRNA expressions of Treg -related FoxP3, IL-35 subunit (p35 and EBI3) and soluble IL-35 receptor subunit (gp130 and IL12Rβ2) in splenic cells were up-regulated significantly in IL-35-treated mice. Compared with the PBS treatment group, IL-35-treated MRL/lpr mice showed an up-regulation of Treg -related genes and the activation of IL-35-related intracellular Janus kinase/signal transducer and activator of transcription signal pathways, thereby indicating the immunoregulatory role of IL-35 in SLE. These in vivo findings may provide a biochemical basis for further investigation of the regulatory mechanisms of IL-35 for the treatment of autoimmune-mediated inflammation.

Characterization of anti-P monoclonal antibodies directed against the ribosomal protein-RNA complex antigen and produced using Murphy Roths large autoimmune-prone mice.

Autoantibodies, including anti-ribosomal P proteins (anti-P), are thought to be produced by an antigen-driven immune response in systemic lupus erythematosus (SLE). To test this hypothesis, we reconstituted the ribosomal antigenic complex in vitro using human P0, phosphorylated P1 and P2 and a 28S rRNA fragment covering the P0 binding site, and immunized Murphy Roths large (MRL)/lrp lupus mice with this complex without any added adjuvant to generate anti-P antibodies. Using hybridoma technology, we subsequently obtained 34 clones, each producing an anti-P monoclonal antibody (mAb) that recognized the conserved C-terminal tail sequence common to all three P proteins. We also obtained two P0-specific monoclonal antibodies, but no antibody specific to P1, P2 or rRNA fragment. Two types of mAbs were found among these anti-P antibodies: one type (e.g. 9D5) reacted more strongly with the phosphorylated P1 and P2 than that with their non-phosphorylated forms, whereas the other type (e.g. 4H11) reacted equally with both phosphorylated and non-phosphorylated forms of P1/P2. Both 9D5 and 4H11 inhibited the ribosome/eukaryotic elongation factor-2 (eEF-2)-coupled guanosine triphosphate (GTP)ase activity. However, preincubation with a synthetic peptide corresponding to the C-terminal sequence common to all three P proteins, but not the peptide that lacked the last three C-terminal amino acids, mostly prevented the mAb-induced inhibition of GTPase activity. Thus, at least two types of anti-P were produced preferentially following the immunization of MRL mice with the reconstituted antigenic complex. Presence of multiple copies of the C-termini, particularly that of the last three C-terminal amino acid residues, in the antigenic complex appears to contribute to the immunogenic stimulus.

The Murphy Roths Large (MRL) mouse strain is naturally resistant to high fat diet-induced hyperglycemia

ObjectiveDue to their previously identified naturally and chronically increased levels of skeletal muscle pAMPK we hypothesized and now investigated whether the MRL/MpJ (MRL) mice would be resistant to high fat diet (HFD)-induced metabolic changes. Materials/methodsThree-week old male MRL and control C57Bl/6 (B6) mice were randomly assigned to 12weeks of high fat diets (HFD) or control diets (CD). Weekly animal masses and fasting blood glucose measurements were acquired. During the last week of diet intervention, fasted animals were subjected to glucose and insulin tolerance tests. At harvest, tissues were dissected for immunoblots and serum was collected for elisa assays. ResultsThe MRL mouse strain is known for its ability to regenerate ear punch wounds, cardiac cryoinjury, and skeletal muscle disease. Despite gaining weight and increasing their fat deposits the MRL mice were resistant to all other indicators of HFD-induced metabolic alterations assayed. Only the HFD-B6 mice displayed fasting hyperglycemia, hyperinsulinemia and hypersensitivity to glucose challenge. HFD-MRL mice were indistinguishable from their CD-MRL counterparts in these metrics. Skeletal muscles from the HFD-MRL contained heightened levels of pAMPK, even above their CD counterparts. ConclusionsThe MRL mouse strain is the first naturally occurring mouse strain that we are aware of that is resistant to HFD-induced metabolic changes. Furthermore, the increased pAMPK suggests a proximal mechanism for these beneficial metabolic differences. We further hypothesize that these metabolic differences and plasticity provide the basis for the MRL mouse strain's super healing characteristics. This project's ultimate aim is to identify novel therapeutic targets, which specifically increase pAMPK.

The Friend leukaemia virus integration 1 (Fli-1) transcription factor affects lupus nephritis development by regulating inflammatory cell infiltration into the kidney

The transcription factor Friend leukaemia virus integration 1 (Fli-1) is implicated in the pathogenesis of systemic lupus erythematosus in both human patients and murine models of lupus. Murphy Roths large (MRL)/lpr mice and New Zealand mixed (NZM)2410 mice, murine models of lupus, with decreased expression of Fli-1 had significantly prolonged survival and reduced nephritis. Lupus nephritis is a major cause of mortality and morbidity in patients, and inflammatory cell infiltration plays a key role in the development of the disease. To study how the expression of Fli-1 affects the infiltration of inflammatory cells into the kidneys, we generated congenic enhanced green fluorescent protein (GFP) transgenic MRL/lpr mice. A significantly increased number of GFP-expressing inflammatory cells infiltrated the kidneys of wild-type MRL/lpr mice compared to Fli-1 heterozygous (Fli-1(+/-)) MRL/lpr mice after injection of GFP(+) cells. Expression of inflammatory chemokine mRNA, including chemokine (C-C motif) ligand (CCL)2, CCL3, CCL4 and CCL5, was significantly lower in the kidneys from Fli-1(+/-) MRL/lpr mice compared to wild-type littermates. Numbers of infiltrated cells into the kidneys correlate with expression levels of CCL2, CCL4 and CCL5, but not the titres of anti-dsDNA autoantibodies in these mice. Significantly increased inflammatory cells from wild-type MRL/lpr mice infiltrated into kidneys compared to the cells from Fli-1(+/-) MRL/lpr mice. The chemotaxis of inflammatory cells from Fli-1(+/-) MRL/lpr mice towards each chemokine was decreased significantly compared to inflammatory cells from wild-type MRL/lpr mice in the transwell migration assay in vitro. Our results indicate that Fli-1 affects lupus nephritis development by regulating the expression of chemokines in the kidney and the migration of inflammatory cells.

Murine lupus strains differentially model unique facets of human lupus serology

Systemic lupus erythematosus (SLE) is a polygenic autoimmune disease characterized by the production of anti-nuclear autoantibodies that lead to subsequent end organ damage. Previous array-based studies in patients with SLE have shown that high immunoglobulin (Ig)G anti-nuclear autoantibody reactivity was associated with severe renal lupus, whereas IgM polyreactivity was associated with less severe disease. To ascertain how different murine lupus strains recapitulate these different autoantibody profiles seen in patients, serum from New Zealand black (NZB)/NZ white (W) F(1), Murphy Roths large (MRL)/lpr, NZ mixed (M)2410 and BXSB strains were compared using a comprehensive array-based screen. The array results were verified using enzyme-linked immunosorbent assays (ELISAs). Serum from MRL/lpr mice exhibited high levels of IgG anti-nuclear antibodies as well as anti-glomerular antibodies and variable levels of antibodies to myosin, Matrigel and thyroglobulin. Elevated anti-nuclear IgG antibodies were associated with severe nephritis in this strain. In contrast, NZM2410 mice exhibited lower IgG autoantibody levels with less severe nephritis but a significantly higher polyreactive IgM autoantibody profile. ELISA analysis confirmed these results. The NZB/NZW F(1) and BXSB strains exhibited an intermediate serological profile. Hence, just as in patients with SLE, whereas strong IgG reactivity to nuclear antigens is associated with severe renal disease, a polyreactive IgM seroprofile is also less ominous in murine lupus.

Early postmyocardial infarction survival in Murphy Roths Large mice is mediated by attenuated apoptosis and inflammation but depends on genetic background.

The Murphy Roths Large (MRL) mouse, a strain capable of regenerating right ventricular myocardium, has a high postmyocardial infarction (post-MI) survival rate compared with C57BL/6J (C57) mice. The biological processes responsible for this survival advantage are unknown. To assess the effect of genetic background, the LG/J strain, which harbours 75% of the MRL composite genome, was included in the study. The MRL survival advantage versus C57 mice (92 versus 68%, P < 0.05) occurred primarily in the first 5 days; LG/J survival was intermediate (P = n.s.). Microarray data analysis revealed an attenuation of apoptotic (P < 0.05) and stress response transcripts in MRL hearts compared with C57 hearts post-MI. Supporting the microarray results, there were fewer TUNEL-positive cells 1 day post-MI in MRL infarcts compared with C57 infarcts (P = 0.001) and fewer CD45-positive cells in the MRL infarct border zone 2 days post-MI (P < 0.01); the LG/J results were intermediate (P = n.s.). The MRL hearts had smaller infarct scars and attenuated ventricular dilatation 30 days post-MI compared with C57 hearts (P < 0.05). We conclude that the early post-MI survival advantage of MRL mice over the C57 strain is mediated at least in part by reductions in apoptosis and inflammatory infiltration, and that these reductions may influence chronic remodelling. The intermediate survival, apoptosis and inflammation profile of LG/J mice suggests that this high tolerance for MI in the MRL mouse could be derived from its shared genetic background with the LG/J mouse.

The role of p21 in regulating mammalian regeneration

The MRL (Murphy Roths Large) mouse has provided a unique model of adult mammalian regeneration as multiple tissues show this important phenotype. Furthermore, the healing employs a blastema-like structure similar to that seen in amphibian regenerating tissue. Cells from the MRL mouse display DNA damage, cell cycle G2/M arrest, and a reduced level of p21CIP1/WAF. A functional role for p21 was confirmed when tissue injury in an adult p21-/- mouse showed a healing phenotype that matched the MRL mouse, with the replacement of tissues, including cartilage, and with hair follicle formation and a lack of scarring. Since the major canonical function of p21 is part of the p53/p21 axis, we explored the consequences of p53 deletion. A regenerative response was not seen in a p53-/- mouse and the elimination of p53 from the MRL background had no negative effect on the regeneration of the MRL.p53-/- mouse. An exploration of other knockout mice to identify p21-dependent, p53-independent regulatory pathways involved in the regenerative response revealed another significant finding showing that elimination of transforming growth factor-β1 displayed a healing response as well. These results are discussed in terms of their effect on senescence and differentiation.

Mechanisms of improved wound healing in Murphy Roths Large (MRL) mice after skin transplantation

Mechanisms of improved wound healing in Murphy Roths Large (MRL) mice after skin transplantation

Mechanisms of improved wound healing in Murphy Roths Large (MRL) mice after skin transplantation

Scars arise in the late phase of wound healing and are characterized by fibroplasia. Previous controversial studies have discussed the regenerative wound healing capacity of Murphy Roths Large (MRL) mice. The aim of this study was to investigate the mechanisms of improved wound healing in a skin transplantation model. Skin grafts from MRL and haplotypically identical B10.BR mice were cross-transplanted. At day 10, B10.BR and MRL grafts on B10.BR recipients deposited collagen and showed severe apoptosis. Grafts of MRL recipients were not affected by such alterations and showed an enhanced healing progress. They were characterized by higher partial pressure of tissue oxygen, increased microcirculation, exceptionally intense neovascularization, and a blunted inflammatory response. This phenotype was accompanied by increased vascular endothelial growth factor expression, augmented by enhanced signal transducer and activator of transcription 3 (STAT3) phosphorylation. These effects were combined with a decreased STAT1 expression and phosphorylation. STAT1 pattern variation was associated with decreased Smad7 levels. Furthermore, MRL recipients showed improved stem cell recruitment to the wound area. The basic accelerated wound healing mechanism in MRL mice found in this skin transplantation model is improved engraftment; this is based on enhanced neovascularization and reduced inflammation. These effects are most likely due to higher vascular endothelial growth factor levels and changes in the STAT/Smad signal pathway, which may enhance transforming growth factor-β signaling, reducing proinflammatory responses.