Novel collagen glomerulopathy in a homotrimeric type I collagen mouse (oim)

Murine Animal Models in Osteogenesis Imperfecta: The Quest for Improving the Quality of Life

Osteogenesis imperfecta is a rare genetic disorder characterized by bone fragility, due to alterations in the type I collagen molecule. It is a very heterogeneous disease, both genetically and phenotypically, with a high variability of clinical phenotypes, ranging from mild to severe forms, the most extreme cases being perinatal lethal. There is no curative treatment for OI, and so great efforts are being made in order to develop effective therapies. In these attempts, the in vivo preclinical studies are of paramount importance; therefore, serious analysis is required to choose the right murine OI model able to emulate as closely as possible the disease of the target OI population. In this review, we summarize the features of OI murine models that have been used for preclinical studies until today, together with recently developed new murine models. The bone parameters that are usually evaluated in order to determine the relevance of new developing therapies are exposed, and finally, current and innovative therapeutic strategies attempts considered in murine OI models, along with their mechanism of action, are reviewed. This review aims to summarize the in vivo studies developed in murine models available in the field of OI to date, in order to help the scientific community choose the most accurate OI murine model when developing new therapeutic strategies capable of improving the quality of life.

Collagen (I) homotrimer potentiates the osteogenesis imperfecta (oim) mutant allele and reduces survival in male mice

The osteogenesis imperfecta murine (oim) model with solely homotrimeric (α1)3 type I collagen, owing to a dysfunctional α2(I) collagen chain, has a brittle bone phenotype, implying that the (α1)2(α2)1 heterotrimer is required for physiological bone function. Here, we comprehensively show, for the first time, that mice lacking the α2(I) chain do not have impaired bone biomechanical or structural properties, unlike oim homozygous mice. However, Mendelian inheritance was affected in male mice of both lines, and male mice null for the α2(I) chain exhibited age-related loss of condition. Compound heterozygotes were generated to test whether gene dosage was responsible for the less-severe phenotype of oim heterozygotes, after allelic discrimination showed that the oim mutant allele was not downregulated in heterozygotes. Compound heterozygotes had impaired bone structural properties compared to those of oim heterozygotes, albeit to a lesser extent than those of oim homozygotes. Hence, the presence of heterotrimeric type I collagen in oim heterozygotes alleviates the effect of the oim mutant allele, but a genetic interaction between homotrimeric type I collagen and the oim mutant allele leads to bone fragility.

Evaluation of 4% stabilized Sodium Hypochlorite activity in the repair of cutaneous excisional wounds in mice

Wounds are conditions largely present in the clinical routine, and even though frequent, their complete resolution can be challenging. Several solutions can aid or stimulate the healing process, and for this reason, this work used a stabilized solution of 4% sodium hypochlorite for the treatment of excisional wounds in mice. This study was carried out in two distinct stages: in the first stage, the optimal concentration of the chlorinated solution was determined by using the sponge implantation technique in mouse subcutaneous tissue to evaluate the dose-response curve; and in the second phase, this concentration was tested in an experimental model of excisional skin wounds in mice. Soluble collagen, hemoglobin, myeloperoxidase (MPO) and N-acetyl-β-D-glycosaminidase (NAG) activity were assessed, and total, type I and type III collagen deposition were quantified in both stages. Based on the results presented in the sponge implantation study, the chlorinated solution at 150 ppm (0.015%) was chosen for use in a preclinical trial of skin healing in mice. At 1, 3, 7 and 14 days of treatment, the % wound area repair in the group treated with 150 ppm chlorinated solution was higher when compared to the control group, with statistical differences at all time points (*p≤ 0.05 and **p≤ 0.01). 150 ppm chlorinated solution obtained from a stabilized 4% sodium hypochlorite solution was effective in accelerating cutaneous excision wound repair in mice, showing a positive influence on tissue repair.

Recombinant sugarcane cystatin CaneCPI-5 down regulates inflammation and promotes angiogenesis and collagen deposition in a mouse subcutaneous sponge model

Cystatins are natural inhibitors of cysteine peptidases that are found practically in all living organisms. CaneCPI-5 is a sugarcane cystatin with inhibitory activity against human cathepsins B, K and L, which are cysteine proteases highly expressed in a variety of pathological conditions, usually marked by persistent inflammation and processing of the extracellular matrix. This work evaluated the effects of daily administration of the recombinant cystatin CaneCPI-5 [0.01, 0.1 or 1.0 μg in 10 μL of Phosphate-Buffered Saline (PBS)] on the inflammatory, angiogenic and fibrogenic components during chronic inflammatory response induced by subcutaneous sponge implants. The anti-inflammatory effect of treatment with CaneCPI-5 was confirmed by reduction of the levels of the pro-inflammatory mediators TNF-α, CXCL1 and CCL2/JE/MCP-1, as well as the activity of the myeloperoxidase and n-acetyl-β-D-glucosaminidase. Treatment with CaneCPI-5 promoted angiogenesis in the implants, increasing the production of cytokines VEGF and FGF and the formation of new blood vessels. Finally, the administration of the recombinant cystatin favored the production of the pro-fibrogenic cytokine TGF-β1 and collagen deposition next to the implants. Together, these results show the potential therapeutic application of CaneCPI-5 as an anti-inflammatory agent, capable of favoring angiogenesis and fibrogenesis processes, necessary for tissue repair.

Transforming growth factor-β1/Smad3-independent epithelial-mesenchymal transition in type I collagen glomerulopathy

The glomerulofibrotic Col1a2-deficient mouse model demonstrates glomerular homotrimeric type I collagen deposition in mesangial and subendothelial spaces. In this report, we investigate the role of transforming growth factor β1 (TGF-β1) in myofibroblast activation and epithelial-mesenchymal transition (EMT) in this glomerulopathy. Immunohistochemical analyses of glomerular α-sma, desmin, vimentin, and proliferating cell nuclear antigen demonstrated parietal epithelial cell proliferation and EMT in late stages of the glomerulopathy in the Col1a2-deficient mice. Glomerular TGF-β1 RNA and protein were not elevated in 1- and 3-month-old mice as determined by quantitative reverse transcriptase-polymerase chain reaction and protein immunoassay analyses. To investigate further whether TGF-β1 plays a role in the glomerulopathy outside of the 1- and 3-month time periods, the Col1a2-deficient mice were bred with Smad3 knockout mice. If the glomerular fibrosis in the Col1a2-deficient mice is mediated by the TGF-β1/Smad3 transcription pathway, it was hypothesized that the resultant Col1a2-deficient/Smad3-deficient mice would exhibit attenuated glomerular homotrimer deposition. However, the Col1a2-deficient/Smad3-deficient kidneys were similarly affected as compared to age-matched Col1a2-deficient kidneys, suggesting that homotrimeric type I collagen deposition in the Col1a2-deficient mouse is independent of TGF-β1/Smad3 signaling. Deposition of homotrimeric type I collagen appears to be the initiating event in this glomerulopathy, providing evidence that EMT and myofibroblast activation occur following initiation, consistent with a secondary wound-healing response independent of TGF-β1.

A mutation in Ampd2 is associated with nephrotic syndrome and hypercholesterolemia in mice

Background

Previously, we identified three loci affecting HDL-cholesterol levels in a screen for ENU-induced mutations in mice and discovered two mutated genes. We sought to identify the third mutated gene and further characterize the mouse phenotype.

Methods

We engaged, DNA sequencing, gene expression profiling, western blotting, lipoprotein characterization, metabolomics assessment, histology and electron microscopy in mouse tissues.

Results

We identify the third gene as Ampd2, a liver isoform of AMP Deaminase (Ampd), a central component of energy and purine metabolism pathways. The causative mutation was a guanine-to-thymine transversion resulting in an A341S conversion in Ampd2. Ampd2 homozygous mutant mice exhibit a labile hypercholesterolemia phenotype, peaking around 9 weeks of age (251 mg/dL vs. wildtype control at 138 mg/dL), and was evidenced by marked increases in HDL, VLDL and LDL. In an attempt to determine the molecular connection between Ampd2 dysfunction and hypercholesterolemia, we analyzed hepatic gene expression and found the downregulation of Ldlr, Hmgcs and Insig1 and upregulation of Cyp7A1 genes. Metabolomic analysis confirmed an increase in hepatic AMP levels and a decrease in allantoin levels consistent with Ampd2 deficiency, and increases in campesterol and β-sitosterol. Additionally, nephrotic syndrome was observed in the mutant mice, through proteinuria, kidney histology and effacement and blebbing of podocyte foot processes by electron microscopy.

Conclusion

In summary we describe the discovery of a novel genetic mouse model of combined transient nephrotic syndrome and hypercholesterolemia, resembling the human disorder.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-511X-13-167) contains supplementary material, which is available to authorized users.

How tough is brittle bone? Investigating osteogenesis imperfecta in mouse bone

The multiscale hierarchical structure of bone is naturally optimized to resist fractures. In osteogenesis imperfecta, or brittle bone disease, genetic mutations affect the quality and/or quantity of collagen, dramatically increasing bone fracture risk. Here we reveal how the collagen defect results in bone fragility in a mouse model of osteogenesis imperfecta (oim), which has homotrimeric α1(I) collagen. At the molecular level, we attribute the loss in toughness to a decrease in the stabilizing enzymatic cross-links and an increase in nonenzymatic cross-links, which may break prematurely, inhibiting plasticity. At the tissue level, high vascular canal density reduces the stable crack growth, and extensive woven bone limits the crack-deflection toughening during crack growth. This demonstrates how modifications at the bone molecular level have ramifications at larger length scales affecting the overall mechanical integrity of the bone; thus, treatment strategies have to address multiscale properties in order to regain bone toughness. In this regard, findings from the heterozygous oim bone, where defective as well as normal collagen are present, suggest that increasing the quantity of healthy collagen in these bones helps to recover toughness at the multiple length scales.

Deficient degradation of homotrimeric type I collagen, α1(I)3 glomerulopathy in oim mice

Col1a2-deficient (oim) mice synthesize homotrimeric type I collagen due to nonfunctional proα2(I) collagen chains. Our previous studies revealed a postnatal, progressive type I collagen glomerulopathy in this mouse model, but the mechanism of the sclerotic collagen accumulation within the renal mesangium remains unclear. The recent demonstration of the resistance of homotrimeric type I collagen to cleavage by matrix metalloproteinases (MMPs), led us to investigate the role of MMP-resistance in the glomerulosclerosis of Col1a2-deficient mice. We measured the pre- and post-translational expression of type I collagen and MMPs in glomeruli from heterozygous and homozygous animals. Both the heterotrimeric and homotrimeric isotypes of type I collagen were equally present in whole kidneys of heterozygous mice by immunohistochemistry and biochemical analysis, but the sclerotic glomerular collagen was at least 95-98% homotrimeric, suggesting homotrimeric type I collagen is the pathogenic isotype of type I collagen in glomerular disease. Although steady-state MMP and Col1a1 mRNA levels increased with the disease progression, we found these changes to be a secondary response to the deficient clearance of MMP-resistant homotrimers. Increased renal MMP expression was not sufficient to prevent homotrimeric type I collagen accumulation.

Dietary fluoride restriction does not alter femoral biomechanical strength in col1a2-deficient (oim) mice with type I collagen glomerulopathy

Osteogenesis imperfecta (OI) is a clinically and genetically heterogeneous disease due primarily to mutations in the type I procollagen genes, COL1A1 and COL1A2, causing bone deformity and numerous lifetime fractures. OI murine (oim) model mice carry a mutation in the col1a2 gene causing aberrant production of homotrimeric type I collagen [α1(I)(3)], leading to bone fragility and glomerular accumulation of type I collagen. Previous studies demonstrated that heterozygous (+/oim) and homozygous (oim/oim) mice have elevated tibiae fluoride concentrations but reduced femoral biomechanics. However, it is unclear whether these 2 variables are causally related, because impaired renal function could reduce urinary fluoride excretion, thus elevating bone fluoride concentrations regardless of disease status. Our goal in this study was to determine whether dietary fluoride restriction would improve femoral biomechanics in oim mice. Wild-type, +/oim, and oim/oim mice were fed a control (5 mg/kg fluoride) or fluoride-restricted diet (0 mg/kg fluoride) for ∼13 wk, at which time plasma and femora were analyzed for fluoride concentrations and bone biomechanical properties. In wild-type, +/oim, and oim/oim mice, dietary fluoride restriction reduced femoral fluoride burden by 54-74%, respectively (P < 0.05), without affecting glomerular collagen deposition. Oim/oim mice fed the fluoride-restricted diet had reduced material tensile strength (P < 0.05) compared with oim/oim mice fed the control diet. However, dietary fluoride restriction did not affect stiffness or whole bone femoral breaking strength, regardless of genotype. These data suggest that oim mice have reduced bone strength due to homotrimeric type I collagen, independent of bone fluoride content.

Biological characteristics of stem cells from foetal, cord blood and extraembryonic tissues

Foetal stem cells (FSCs) can be isolated during gestation from many different tissues such as blood, liver and bone marrow as well as from a variety of extraembryonic tissues such as amniotic fluid and placenta. Strong evidence suggests that these cells differ on many biological aspects such as growth kinetics, morphology, immunophenotype, differentiation potential and engraftment capacity in vivo. Despite these differences, FSCs appear to be more primitive and have greater multi-potentiality than their adult counterparts. For example, foetal blood haemopoietic stem cells proliferate more rapidly than those found in cord blood or adult bone marrow. These features have led to FSCs being investigated for pre- and post-natal cell therapy and regenerative medicine applications. The cells have been used in pre-clinical studies to treat a wide range of diseases such as skeletal dysplasia, diaphragmatic hernia and respiratory failure, white matter damage, renal pathologies as well as cancers. Their intermediate state between adult and embryonic stem cells also makes them an ideal candidate for reprogramming to the pluripotent status.

Generalized connective tissue disease in Crtap-/- mouse

Mutations in CRTAP (coding for cartilage-associated protein), LEPRE1 (coding for prolyl 3-hydroxylase 1 [P3H1]) or PPIB (coding for Cyclophilin B [CYPB]) cause recessive forms of osteogenesis imperfecta and loss or decrease of type I collagen prolyl 3-hydroxylation. A comprehensive analysis of the phenotype of the Crtap-/- mice revealed multiple abnormalities of connective tissue, including in the lungs, kidneys, and skin, consistent with systemic dysregulation of collagen homeostasis within the extracellular matrix. Both Crtap-/- lung and kidney glomeruli showed increased cellular proliferation. Histologically, the lungs showed increased alveolar spacing, while the kidneys showed evidence of segmental glomerulosclerosis, with abnormal collagen deposition. The Crtap-/- skin had decreased mechanical integrity. In addition to the expected loss of proline 986 3-hydroxylation in alpha1(I) and alpha1(II) chains, there was also loss of 3Hyp at proline 986 in alpha2(V) chains. In contrast, at two of the known 3Hyp sites in alpha1(IV) chains from Crtap-/- kidneys there were normal levels of 3-hydroxylation. On a cellular level, loss of CRTAP in human OI fibroblasts led to a secondary loss of P3H1, and vice versa. These data suggest that both CRTAP and P3H1 are required to maintain a stable complex that 3-hydroxylates canonical proline sites within clade A (types I, II, and V) collagen chains. Loss of this activity leads to a multi-systemic connective tissue disease that affects bone, cartilage, lung, kidney, and skin.

Null mutations in LEPRE1 and CRTAP cause severe recessive osteogenesis imperfecta

Classical osteogenesis imperfecta (OI) is a dominant genetic disorder of connective tissue caused by mutations in either of the two genes encoding type I collagen, COL1A1 and COL1A2. Recent investigations, however, have generated a new paradigm for OI incorporating many of the prototypical features that distinguish dominant and recessive conditions, within a type I collagen framework. We and others have shown that the long-sought cause of the recessive form of OI, first postulated in the Sillence classification, lies in defects in the genes encoding cartilage-associated protein (CRTAP) or prolyl 3-hydroxylase 1 (P3H1/LEPRE1). Together with cyclophilin B (PPIB), CRTAP and P3H1 comprise the collagen prolyl 3-hydroxylation complex, which catalyzes a specific posttranslational modification of types I, II, and V collagen, and may act as a general chaperone. Patients with mutations in CRTAP or LEPRE1 have a lethal to severe osteochondrodystrophy that overlaps with Sillence types II and III OI but has distinctive features. Infants with recessive OI have white sclerae, undertubulation of the long bones, gracile ribs without beading, and a small to normal head circumference. Those who survive to childhood or the teen years have severe growth deficiency and extreme bone fragility. Most causative mutations result in null alleles, with the absence or severe reduction of gene transcripts and proteins. As expected, 3-hydroxylation of the Pro986 residue is absent or severly reduced, but bone severity and survival length do not correlate with the extent of residual hydroxylation. Surprisingly, the collagen produced by cells with an absence of Pro986 hydroxylation has helical overmodification by lysyl hydroxylase and prolyl 4-hydroxylase, indicating that the folding of the collagen helix has been substantially delayed.

Pericytes and perivascular fibroblasts are the primary source of collagen-producing cells in obstructive fibrosis of the kidney

Understanding the origin of scar-producing myofibroblasts is vital in discerning the mechanisms by which fibrosis develops in response to inflammatory injury. Using a transgenic reporter mouse model expressing enhanced green fluorescent protein (GFP) under the regulation of the collagen type I, alpha 1 (coll1a1) promoter and enhancers, we examined the origins of coll1a1-producing cells in the kidney. Here we show that in normal kidney, both podocytes and pericytes generate coll1a1 transcripts as detected by enhanced GFP, and that in fibrotic kidney, coll1a1-GFP expression accurately identifies myofibroblasts. To determine the contribution of circulating immune cells directly to scar production, wild-type mice, chimeric with bone marrow from coll-GFP mice, underwent ureteral obstruction to induce fibrosis. Histological examination of kidneys from these mice showed recruitment of small numbers of fibrocytes to the fibrotic kidney, but these fibrocytes made no significant contribution to interstitial fibrosis. Instead, using kinetic modeling and time course microscopy, we identified coll1a1-GFP-expressing pericytes as the major source of interstitial myofibroblasts in the fibrotic kidney. Our studies suggest that either vascular injury or vascular factors are the most likely triggers for pericyte migration and differentiation into myofibroblasts. Therefore, our results serve to refocus fibrosis research to injury of the vasculature rather than injury to the epithelium.

Segregation of type I collagen homo- and heterotrimers in fibrils

Normal type I collagen is a heterotrimer of two alpha1(I) and one alpha2(I) chains, but various genetic and environmental factors result in synthesis of homotrimers that consist of three alpha1(I) chains. The homotrimers completely replace the heterotrimers only in rare recessive disorders. In the general population, they may compose just a small fraction of type I collagen. Nevertheless, they may play a significant role in pathology; for example, synthesis of 10-15% homotrimers due to a polymorphism in the alpha1(I) gene may contribute to osteoporosis. Homotrimer triple helices have different stability and less efficient fibrillogenesis than heterotrimers. Their fibrils have different mechanical properties. However, very little is known about their molecular interactions and fibrillogenesis in mixtures with normal heterotrimers. Here we studied the kinetics and thermodynamics of fibril formation in such mixtures by combining traditional approaches with 3D confocal imaging of fibrils, in which homo- and heterotrimers were labeled with different fluorescent colors. In a mixture, following a temperature jump from 4 to 32 degrees C, we observed a rapid increase in turbidity most likely caused by formation of homotrimer aggregates. The aggregates promoted nucleation of homotrimer fibrils that served as seeds for mixed and heterotrimer fibrils. The separation of colors in confocal images indicated segregation of homo- and heterotrimers at a subfibrillar level throughout the process. The fibril color patterns continued to change slowly after the fibrillogenesis appeared to be complete, due to dissociation and reassociation of the pepsin-treated homo- and heterotrimers, but this remixing did not significantly reduce the segregation even after several days. Independent homo- and heterotrimer solubility measurements in mixtures confirmed that the subfibrillar segregation was an equilibrium property of intermolecular interactions and not just a kinetic phenomenon. We argue that the subfibrillar segregation may exacerbate effects of a small fraction of alpha1(I) homotrimers on formation, properties, and remodeling of collagen fibers.

Transplantation of human fetal mesenchymal stem cells improves glomerulopathy in a collagen type I alpha 2-deficient mouse

Fetal mesenchymal stem cell (fetal MSC) therapy has potential to treat genetic diseases with early onset, including those affecting the kidney and urinary tract. A collagen type I alpha 2-deficient mouse has a deletion in the alpha2 chain of the procollagen type I gene, resulting in the synthesis of abnormal alpha1(I)(3) homotrimers, which replace normal alpha 1(I)2 alpha 2(I)1 heterotrimers and a glomerulopathy. We first confirmed that col1 alpha 2-deficient homozygous mice show abnormal collagen deposition in the glomeruli, which increases in frequency and severity with postnatal age. Intrauterine transplantation of human MSCs from first trimester fetal blood led postnatally to a reduction of abnormal homotrimeric collagen type I deposition in the glomeruli of 4-12 week-old col1 alpha 2-deficient mice. Using bioluminescence imaging, in situ hybridization and immunohistochemistry in transplanted col1 alpha 2-deficient mice, we showed that the damaged kidneys preferentially recruited donor cells in glomeruli, around mesangial cells. Real-time RT-PCR demonstrated that this effect was seen at an engraftment level of 1% of total cells in the kidney, albeit higher in glomeruli. We conclude that intrauterine transplantation of human fetal MSCs improves renal glomerulopathy in a collagen type I-deficient mouse model. These data support the feasibility of prenatal treatment for hereditary renal diseases.

Type I collagen glomerulopathy: postnatal collagen deposition follows glomerular maturation

In chronic renal disease, the progressive accumulation of collagen and other extracellular matrix proteins in the mesangium results in fibrosis, glomerulosclerosis, and eventual renal failure. Mice deficient in proalpha2(I) collagen are not only a model of osteogenesis imperfecta but also accumulate fibrillar homotrimeric type I collagen in the mesangium. This accumulation spreads to the subendothelial space in the peripheral capillary loops. Picosirius red staining of kidney sections demonstrates that in comparison to wild-type mice, Col1a2-deficient homozygous and heterozygous mice exhibit abnormal glomerular collagen deposition in a gene dosage-dependent manner. The glomerulopathy initiates during the first postnatal week, appears progressive following the pattern of glomerular maturation and results in albuminuria in severely affected animals. In situ hybridization revealed no gross differences in steady-state proalpha1(I) and proalpha2(I) collagen mRNA levels among the three genotypes. Quantitative reverse transcriptase-polymerase chain reaction, however, using whole kidney sections showed a twofold increase in steady-state proalpha1(I) collagen mRNA in 1-month homozygous Col1a2-deficient animals compared with wild-type and heterozygous animals. We suggest that glomerular collagen deposition seen in the osteogenesis imperfecta model mice is, in part, owing to pretranslational mechanisms and may represent an over compensation of wound healing.

Organ-specific collagen expression: implications for renal disease

Chronic kidney disease is characterized by progressive accumulation of extracellular matrix and scarring, leading to the loss of kidney function. Excess deposition of the collagen family of proteins is the hallmark of kidney fibrosis. In this review, we survey the collagens that are associated with renal disease and we highlight the use of a transgenic approach to identify cis-acting sequences in the collagen type I promoter which are capable of directing collagen type I expression specifically in the kidney. Ultimately it may be possible to use this approach to halt the accumulation of collagen selectively in this organ.

Cardiovascular and renal disease in the adolescent guinea pig after chronic placental insufficiency

OBJECTIVE

The aim of this study was to determine the long-term effects of chronic placental insufficiency on the metabolic state and organ structure in the fetal and adolescent guinea pig.

STUDY DESIGN

The maternal uterine artery was ligated at day 28-30 to reduce placental function and restrict fetal growth. Whole body and tissue weights and plasma metabolites were determined at 60 days of gestation and 8 weeks of age; tissue structure was determined at the latter age in restricted and control offspring.

RESULTS

Fetal growth restriction increased fibrosis in the heart and kidneys (P < .05), increased aortic wall thickening (P < .01), reduced the number of glomeruli in the kidneys (P < .05), and increased the plasma urea and chloride in adolescent offspring.

CONCLUSION

This study demonstrates that diseases in the heart, aorta, and kidneys that result from an adverse prenatal environment are evident at adolescence and may contribute to subsequent adult disease.