Cortical bone properties in the Brtl/+ mouse model of Osteogenesis imperfecta as evidenced by acoustic transmission microscopy

Higher skeletal fragility has been established for the Brtl/+ mouse model of osteogenesis imperfecta at the whole bone level, but previous investigations of mechanical properties at the bone material level were inconclusive. Bone material was analyzed separately at endosteal (ER) and periosteal regions (PR) on transverse femoral midshaft sections for 2-month old mice (wild-type n = 6; Brtl/+ n = 6). Quantitative backscattered electron imaging revealed that the mass density computed from mineral density maps was higher in PR than in ER for both wild-type (+2.1%, p < 0.05) and Brtl/+ mice (+1.8%, p < 0.05). Electron induced X-ray fluorescence analysis indicated significantly lower atomic Ca/P ratios and higher Na/Ca, Mg/Ca and K/Ca ratios in PR bone compared to ER independently of genotype. Second harmonic generation microscopy indicated that the occurrence of periodically alternating collagen orientation in ER of Brtl/+ mice was strongly reduced compared to wild-type mice. Scanning acoustic microscopy in time of flight mode revealed that the sound velocity and Young's modulus (estimated based on sound velocity and mass density maps) were significantly greater in PR (respectively +6% and +15%) compared to ER in wild-type mice but not in Brtl/+ mice. ER sound velocity and Young's modulus were significantly increased in Brtl/+ mice (+9.4% and +22%, respectively) compared to wild-type mice. These data demonstrate that the Col1a1 G349C mutation in Brtl/+ mice affects the mechanical behavior of bone material predominantly in the endosteal region by altering the collagen orientation.

Non-surgical alternatives to invasive procedures in mice

We have developed and validated catheterization protocols in mice that allow for simultaneous infusion and sampling. A sampling catheter was inserted in the lateral vein of the tail, while the animals were infused either intravenously or intragastrically through a second catheter placed in the contralateral lateral vein or via an intragastric catheter, respectively. The applicability of these methods of infusion and blood sampling were validated by conducting urea kinetics utilizing stable isotopes. These non-surgical procedures are non-invasive, inexpensive, fast to perform and animals do not require a recovery period before their use.

Tiered approaches to chromatographic bioanalytical method performance evaluation: recommendation for best practices and harmonization from the Global Bioanalysis Consortium harmonization team

The A2 harmonization team, a part of the Global Bioanalysis Consortium (GBC), focused on defining possible tiers of chromatographic-based bioanalytical method performance. The need for developing bioanalytical methods suitable for the intended use is not a new proposal and is already referenced in regulatory guidance language. However, the practical implementation of approaches that differ from the well-established full validation requirements has proven challenging. Advances in technologies, the need to progress drug development more efficiently, and emerging new drug compound classes support the use of categorized tiers of bioanalytical methods. This paper incorporated the input from an international team of experienced bioanalysts to surmise the advantages and the challenges of tiered approaches and to provide recommendations on paths forward.

Fracture healing with alendronate treatment in the Brtl/+ mouse model of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable bone dysplasia characterized by increased skeletal fragility. Patients are often treated with bisphosphonates to attempt to reduce fracture risk. However, bisphosphonates reside in the skeleton for many years and long-term administration may impact bone material quality. Acutely, there is concern about risk of non-union of fractures that occur near the time of bisphosphonate administration. This study investigated the effect of alendronate, a potent aminobisphosphonate, on fracture healing. Using the Brtl/+ murine model of type IV OI, tibial fractures were generated in 8-week-old mice that were untreated, treated with alendronate before fracture, or treated before and after fracture. After 2, 3, or 5 weeks of healing, tibiae were assessed using microcomputed tomography (μCT), torsion testing, quantitative histomorphometry, and Raman microspectroscopy. There were no morphologic, biomechanical or histomorphometric differences in callus between untreated mice and mice that received alendronate before fracture. Alendronate treatment before fracture did not cause a significant increase in cartilage retention in fracture callus. Both Brtl/+ and WT mice that received alendronate before and after fracture had increases in the callus volume, bone volume fraction and torque at failure after 5 weeks of healing. Raman microspectroscopy results did not show any effects of alendronate in wild-type mice, but calluses from Brtl/+ mice treated with alendronate during healing had a decreased mineral-to-matrix ratio, decreased crystallinity and an increased carbonate-to-phosphate ratio. Treatment with alendronate altered the dynamics of healing by preventing callus volume decreases later in the healing process. Fracture healing in Brtl/+ untreated animals was not significantly different from animals in which alendronate was halted at the time of fracture.

Deficiency of CRTAP in non-lethal recessive osteogenesis imperfecta reduces collagen deposition into matrix

Deficiency of any component of the ER-resident collagen prolyl 3-hydroxylation complex causes recessive osteogenesis imperfecta (OI). The complex modifies the α1(I)Pro986 residue and contains cartilage-associated protein (CRTAP), prolyl 3-hydroxylase 1 (P3H1) and cyclophilin B (CyPB). Fibroblasts normally secrete about 10% of CRTAP. Most CRTAP mutations cause a null allele and lethal type VII OI. We identified a 7-year-old Egyptian boy with non-lethal type VII OI and investigated the effects of his null CRTAP mutation on collagen biochemistry, the prolyl 3-hydroxylation complex, and collagen in extracellular matrix. The proband is homozygous for an insertion/deletion in CRTAP (c.118_133del16insTACCC). His dermal fibroblasts synthesize fully overmodified type I collagen, and 3-hydroxylate only 5% of α1(I)Pro986. CRTAP transcripts are 10% of control. CRTAP protein is absent from proband cells, with residual P3H1 and normal CyPB levels. Dermal collagen fibril diameters are significantly increased. By immunofluorescence of long-term cultures, we identified a severe deficiency (10-15% of control) of collagen deposited in extracellular matrix, with disorganization of the minimal fibrillar network. Quantitative pulse-chase experiments corroborate deficiency of matrix deposition, rather than increased matrix turnover. We conclude that defects of extracellular matrix, as well as intracellular defects in collagen modification, contribute to the pathology of type VII OI.

Bent helical structure in kinetoplast DNA

We have investigated the unusual physical properties of a restriction fragment of Leishmania tarentolae kinetoplast DNA. A gel-purified fragment comprising slightly more than half of a minicircle was determined by Maxam-Gilbert sequence determination to be 490 base pairs (bp) in length. This fragment has dramatically anomalous electrophoretic behavior; it has an apparent size of 450 bp on a 1% agarose gel but migrates as 1,380 bp on a 12% polyacrylamide gel. However, in gel filtration on Sephacryl S-500, the fragment elutes with an apparent size of 375 bp. Finally, it behaves anomalously in electric dichroism experiments. Field-free rotational relaxation times from transient electric dichroism studies are highly sensitive to effective molecular dimensions. The rotational relaxation time of the kinetoplast fragment is smaller than that of a 309-bp control fragment from pBR322. Because rigorous control experiments rule out the possibility that this fragment is modified, these anomalous properties must be dictated by the sequence itself. Fragment behavior indicates that it has an unusually compact configuration; we propose that this molecule contains a region of systematically bent B-DNA. This model accounts for the fragment's difficulty in snaking through the pores of a polyacrylamide gel, its ease in diffusing into Sephacryl beads, and its smaller rotational relaxation time. Bending of this molecule may be caused by periodicities in the DNA sequence.

A type I collagen defect leads to rapidly progressive osteoarthritis in a mouse model

OBJECTIVE

This study was undertaken to test the hypothesis that abnormalities of the subchondral bone can result in osteoarthritis (OA).

METHODS

We used a knockin model of human osteogenesis imperfecta, the Brittle IV (Brtl) mouse, in which defective type I collagen is expressed in bone. OA in individual mice was documented by micro-magnetic resonance imaging (micro-MRI) and micro-computed tomography (micro-CT). Alterations in the knee joints were confirmed by histopathologic and immunohistochemical analysis. In addition, atomic force microscopy (AFM) was used to assess the ultrastructure of the articular cartilage and subchondral bone matrix.

RESULTS

Brtl mice had decreased integrity of bone but initially normal articular cartilage. However, by the second month of life, Brtl mice developed alterations of the cartilage that were characteristic of OA, as documented by micro-CT, micro-MRI, and histologic evaluation. In addition, chondrocyte loss and breakdown of the collagen matrix in the residual cartilage were demonstrated using AFM.

CONCLUSION

The Brtl mouse model demonstrates that progressive destruction of articular cartilage characteristic of OA may be secondary to altered architecture of the underlying subchondral bone.

Inflammatory biomarkers, disease activity and spinal disease measures in patients with ankylosing spondylitis after treatment with infliximab

Objective:

To evaluate the relationship between biomarker levels and disease activity and the spinal inflammation detected by magnetic resonance imaging (MRI) in patients with ankylosing spondylitis (AS).

Methods:

Patients with AS were randomly assigned in a 3:8 ratio to receive infusions of placebo or 5 mg/kg infliximab at weeks 0, 2, 6, 12 and 18. Sera were collected for biomarker analysis at weeks 0, 2 and 24 and were analysed for levels of interleukin-6 (IL-6), vascular endothelial growth factor (VEGF) and C-reactive protein (CRP). Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) scores and pre- and post-gadolinium T1 and short τ inversion recovery MRIs were collected at baseline and week 24.

Results:

Significantly greater reductions in IL-6, VEGF and CRP were observed at weeks 2 and 24 in the infliximab group compared with the placebo group (all p<0.001). Baseline IL-6 levels >7.38 pg/ml and CRP levels >1.5 mg/dl were associated with increased rates of clinical response after 24 weeks. Multiple regression analyses showed that reductions from baseline to week 2 in IL-6, but not CRP or VEGF, were significantly associated with reductions in MRI activity and BASDAI scores from baseline to week 24 in the infliximab group (p<0.001).

Conclusions:

Significant reductions in IL-6, VEGF and CRP were observed with infliximab compared with placebo. High levels of baseline IL-6 and CRP were associated with clinical response after infliximab treatment. Early reductions in IL-6 were significantly associated with improvements in disease activity and the spinal inflammation detected by MRI.

Biochemical screening of type I collagen in osteogenesis imperfecta: detection of glycine substitutions in the amino end of the alpha chains requires supplementation by molecular analysis

BACKGROUND

The biochemical test for osteogenesis imperfecta (OI) detects structural abnormalities in the helical region of type I collagen as delayed electrophoretic migration of alpha chains on SDS-urea-PAGE. Sensitivity of this test is based on overmodification of alpha chains in helices with a glycine substitution or other structural defect. The limits of detectability have not been reported.

METHODS

We compared the collagen electrophoretic migration of 30 probands (types III or IV OI) with known mutations in the amino half of the alpha1(I) and alpha2(I) chains. Differences in sensitivity were examined by 5% and 6% SDS-urea-PAGE, and with respect to alpha chain, location along the chain, and substituting amino acid.

RESULTS

Sensitivity was enhanced on 5% gels, and by examination of intracellular and secreted collagen. In alpha1(I), substitutions in the first 100 residues were not detectable; 7% of cases in the current Mutation Consortium database are in this region. alpha1(I) substitutions between residues 100 and 230 were variably detectable, while those after residue 232 were all detected. In alpha2(I), variability of electrophoretic detection extended through residue 436. About a third of cases in the Consortium database are located in the combined variable detection region. Biochemical sensitivity did not correlate with substituting residue.

CONCLUSIONS

Complete testing of probands with normal type I collagen biochemical results requires supplementation by molecular analysis of cDNA or gDNA in the amino third of alpha1(I) and amino half of alpha2(I). Mutation detection in OI is important for counselling, reproductive decisions, exclusion of child abuse, and genotype-phenotype correlations.

Partition of Nitrogen Excretion in Urine and the Feces of Holstein Replacement Heifers

Increasing public concern has been focused on animal production systems as a major nonpoint source of pollution. These studies were conducted to further our understanding of whole-animal N metabolism, N excretion, and its partition between feces and urine in growing dairy heifers. Isocaloric diets [2.31 Mcal of metabolizable energy (ME)/kg of dry matter (DM)], ranging from 12.4 to 34.2 g of N/kg of DM, were fed to Holstein heifers in 2 experiments at approximately 1.8 times maintenance. Diets were formulated to provide 54 to 143% of the ruminal ammonia requirements as predicted by the Cornell Net Carbohydrate and Protein System. Increasing the N content of the diet increased urinary N excretion and N balance, but did not affect fecal N excretion. Holstein heifers fed low N diets were able to maintain growth rates consistent with current recommendations while at the same time reducing N excretion, in particular nitrogenous compounds that are readily converted to ammonia. However, more research is needed before this type of diet is recommended for growing heifers because of possible changes in body composition that may affect future milk production and performance.

Decreased expression of lysyl hydroxylase 2 (LH2) in skin fibroblasts from three Ehlers-Danlos patients does not result from mutations in either the coding or proximal promoter region of the LH2 gene

The Ehlers-Danlos syndromes (EDS) are a heterogeneous group of inherited connective tissue disorders characterized by tissue fragility, hyperelasticity of the skin and joint hypermobility. This phenotype, accompanied by kyphoscoliosis and/or ocular fragility, is present in patients with the autosomal recessive type VI form of EDS. These patients have significantly decreased levels of lysyl hydroxylase (LH) activity, due to mutations in the LH1 gene. LH hydroxylates specific lysine residues in the collagen molecule that are precursors for the formation of cross-links which provide collagen with its tensile strength. No disorder has been directly linked to decreased expression of LH2 and LH3, two other isoforms of LH. This study describes 3 patients with mixed phenotypes of EDS, who have significantly decreased mRNAs for LH2, but normal levels of LH1 and LH3 mRNAs, in their skin fibroblasts. In contrast to the effect of LH1 deficiency in EDS VI patients, the decreased expression of LH2 does not affect LH activity, bifunctional collagen cross-links (measured after reduction as dihydroxylysinonorleucine (DHLNL) and hydroxylysinonorleucine (HLNL)), or helical lysine hydroxylation in these cell lines. Sequence analysis of full length LH2 cDNAs and 1kb of the promoter region of LH2 does not show mutations that could explain the decreased expression of LH2. These results suggest that the deficiency of LH2 in these fibroblasts may be caused by changes in other factors required for the expression of LH2.

Effect of nitrogen intake on nitrogen recycling and urea transporter abundance in lambs

Urea recycling in ruminants has been studied extensively in the past, but the mechanisms regulating the amount of urea recycled or excreted remain obscure. To elucidate the role of urea transporters (UT) in N recycling, nine Dorset-Finn ewe lambs (20.8 +/- 0.8 kg) were fed diets containing 15.5, 28.4, and 41.3 g of N/kg of DM for 25 d. Nitrogen balance and urea N kinetics were measured during the last 3 d of the period. Animals were then slaughtered and mucosa samples from the rumen, duodenum, ileum, and cecum, as well as kidney medulla and liver, were collected. Increasing N intake tended to increase N balance quadratically (1.5, 5.1, and 4.4 +/- 0.86 g of N/d, P < 0.09), and linearly increased urinary N excretion (2.4, 10, and 16.5 +/- 0.86 g N/d, P < 0.001) and plasma urea N concentration (4.3, 20.3, and 28.4 +/- 2.62 mg of urea N/dL, P < 0.001), but did not affect fecal N excretion (5.0 +/- 0.5 g of N/d; P < 0.94). Urea N production (2.4, 11.8, and 19.2 +/- 0.83 g of N/d; P < 0.001) and urinary urea N excretion (0.7, 7.0, and 13.4 +/- 0.73 g N/d; P < 0.001) increased linearly with N intake, as well as with the urea N recycled to the gastrointestinal tract (1.8, 4.8, and 5.8 +/- 0.40 g of N/d, P < 0.001). No changes due to N intake were observed for creatinine excretion (518 +/- 82.4 mg/d; P < 0.69) and clearance (46 +/- 10.7 mL/min; P < 0.56), but urea N clearance increased linearly with N intake (14.9, 24.4, and 34.9 +/- 5.9 mL/min; P < 0.04). Urea N reabsorption by the kidney tended to decrease (66.3, 38.5, 29.1 +/- 12.6%; P < 0.06) with increasing N content of the diet. Increasing the level of N intake increased linearly the weight of the liver as a proportion of BW (1.73, 1.88, and 2.22 +/- 0.15%, P < 0.03) but only tended to increase the weight of the kidneys (0.36, 0.37, and 0.50 +/- 0.05%, P < 0.08). Urea transporter B was present in all the tissues analyzed, but UT-A was detected only in kidney medulla, liver, and duodenum. Among animals on the three diets, no differences (P > 0.10) in UT abundance, quantified by densitometry, were found. Ruminal-wall urease activity decreased linearly (P < 0.02) with increasing level of N intake. Urease activity in duodenal, ileal, and cecal mucosa did not differ from zero (P > 0.10) in lambs on the high-protein diet. In the present experiment, urea transporter abundance in the kidney medulla and the gastrointestinal tract did not reflect the increase in urea-N reabsorption by the kidney and transferred into the gut.

Heterogeneous basis of the type VIB form of Ehlers-Danlos syndrome (EDS VIB) that is unrelated to decreased collagen lysyl hydroxylation

Skin fibroblasts from the majority of patients with the clinical diagnosis of Ehlers-Danlos syndrome type VI (EDS VI; kyphoscoliosis type), have significantly decreased lysyl hydroxylase (LH) activity due to mutations in the LH1 gene (classified as EDS VIA: OMIM no. 225400). A rare condition exists in which patients are clinically similar but have normal levels of LH activity (designated EDS VIB: OMIM no. 229200). To define the biochemical defect, we have examined cultured fibroblasts from four EDS VIB patients for changes in the levels of the mRNAs for LH1, LH2, and LH3, collagen cross-linking patterns, and the extent of lysine hydroxylation of type I collagen alpha chains. Although normal levels of LH1 mRNA were observed in all four patients, in two patients the levels of LH2 mRNA were decreased by >50%, and a similar decrease was observed in LH3 mRNA in the other two patients. A distinct pattern of collagen cross-links, indicative of decreased lysyl hydroxylation, could be identified in EDS VIA patients, but there was no clear correlation between collagen cross-link pattern and changes in the individual LH mRNAs in EDS VIB patients. Linkage to tenascin-X was excluded in these patients. This study suggests that the basis for this form of EDS VI is genetically heterogeneous, and that alternative pathways in addition to lysine hydroxylation of collagen may be affected.

Nitrogen metabolism and recycling in Holstein heifers

To study the effect of dietary N level on urea kinetics and recycling, four Holstein heifers (267 +/- 3.6 kg) were used in a Youden square design. Isocaloric diets with a N content of 1.44, 1.89, 2.50, 2.97, and 3.40% were fed at approximately 1.8 times maintenance intake. Increasing the N content of the diet increased urinary N excretion (P < 0.001) and N balance (P < 0.01), but did not affect the fecal N excretion (P = 0.21). Increasing the level of dietary N, increased urea production (P < 0.001) and excretion (P < 0.001), but no effect (P = 0.24) could be detected in the amount of N recycled to the gut. Urea recycled with the saliva, however, increased (P < 0.001) both in absolute and relative terms, with increasing dietary N. No difference could be detected on the amount of recycled N that was used for anabolism or returned to the ornithine cycle, but less (P = 0.001) N originating from urea was excreted in feces as dietary N increased. Ruminal ammonia concentration increased (P < 0.001) with increasing N intake, but total tract neutral detergent fiber digestibility was depressed only on the lowest N intake diet. No difference (P = 0.30) was detected in ruminal microbial yield among diets, but more (P < 0.003) N was derived from blood urea at low N intakes, and the efficiency of use of the recycled N decreased (P < 0.001) with increasing levels of dietary N. Adaptive changes to low-N diets were a decrease (P < 0.003) in the renal clearance of urea and an increase (P < 0.001) in the gastrointestinal clearance of urea. Urea transporters were present in the rumen wall of the heifers and differentially expressed depending on dietary N content, but their role in the transfer of urea into the rumen remains uncertain. Different mechanisms of N salvage and recycling were involved when animals were fed low-N diets that ensured a supply of endogenous N to the gastrointestinal tract and, due to the reduced contribution of dietary N, an increased efficiency of the N recycled was observed.

The effect of a ruminal nitrogen (N) deficiency in dairy cows: evaluation of the cornell net carbohydrate and protein system ruminal N deficiency adjustment

Twenty-four multiparous and fifteen first lactation Holstein cows averaging 263 days in milk and weighing 614 kg were fed diets adequate or deficient in ruminal nitrogen (N), based on predictions of the Cornell Net Carbohydrate and Protein System (CNCPS). After adjustment to a low crude protein (CP) total mixed rations (TMR; 12.6% CP), the cows were allocated to 13 blocks based on lactation number, milk production, body condition score, and body weight. Within each block, cows were randomly assigned to one of the 3 treatment (TRT) diets (9.4, 11.1 and 14.1% CP for TRT 1, 2, and 3, respectively). All diets contained the same proportion of high moisture corn, chopped grass hay, and minerals, with urea substituted for corn silage as needed to reach the three CP levels. The TRT diets were then fed to the cows for 4 wk. Milk production was significantly affected by TRT: 15.5, 18.8, and 21.7 kg/d for TRT diets 1, 2, and 3, respectively. DMI was increased significantly as the percentage of CP increased from 9.4 to 14.1% CP: 17.6, 20.0, and 21.2 kg/d for TRT diets 1,2, and 3, respectively. CNCPS predictions for production (with and without the N adjustment for ruminal N deficiency) of metabolizable protein (MP) allowable milk were compared with observed milk production. Using the average individual weekly cow data from all 3 TRT, we found that the CNCPS accounted for 72 and 68% of the variation in MP allowable milk without and with the N deficiency adjustment, respectively. The overall mean bias without the N adjustment was 3.3 kg of milk (over prediction model bias of 14.6%, P < 0.001), and the N adjustment reduced the model over-prediction bias to 0.01 kg of milk (P = 0.96).

COL5A1 exon 14 splice acceptor mutation causes a functional null allele, haploinsufficiency of alpha 1(V) and abnormal heterotypic interstitial fibrils in Ehlers-Danlos syndrome II

We studied four affected individuals from a family of three generations with Ehlers-Danlos Syndrome II. Type V collagen transcripts of affected individuals were screened by reverse transcriptase-polymerase chain reaction. Amplification of the exon 9-28 region of alpha1(V) yielded normal and larger products from the proband. Sequencing of cDNA revealed a 100-base pair insertion from the 3'-end of intron 13 between exons 13 and 14 in one allele. The genomic defect was identified as an A(-2)--> G substitution at the exon 14 splice acceptor site. A cryptic acceptor site -100 nucleotide within intron 13 is used instead of the mutant splice site. The insertion shifts the reading frame +1 and results in a stop codon within exon 17. The mutant transcript was much less abundant than normal allele product in untreated cultured fibroblasts but was approximately equimolar in cycloheximide-treated cells, suggesting that the mutation causes nonsense-mediated decay of mRNA. By RNase protection experiments, the level of mutant transcript was determined to be 8% that of the normal transcript in untreated proband fibroblasts. Relative to type I collagen, proband fibroblasts secreted only 65% of the amount of type V collagen secreted by normal controls. Selective salt precipitation of proband secreted collagen provided supportive evidence that the alpha chain composition of type V collagen remains alpha1(V)(2)alpha2(V) even in the context of alpha1(V) haploinsufficiency. Type V collagen incorporates into type I collagen fibrils in the extracellular matrix and is thought to regulate fibril diameter. Transmission electron micrographs of type I collagen fibrils in a proband dermal biopsy showed greater heterogeneity in fibril diameter than in a matched control. The proband had a greater proportion of both larger and smaller fibrils and occasional fibrils with a cauliflower configuration. Unlike the genotype/phenotype relationship seen for type I collagen defects and osteogenesis imperfecta, the null allele in this family appears to cause clinical features similar to those seen in cases with structural alterations in type V collagen.

G76E substitution in type I collagen is the first nonlethal glutamic acid substitution in the alpha1(I) chain and alters folding of the N-terminal end of the helix

The majority of osteogenesis imperfecta (OI) is caused by substitutions for glycine residues in the two alpha chains of type I collagen. Since only 4% of possible nucleotide changes in type I collagen glycine codons would result in a glutamic acid substitution, these are predicted to be infrequent. Only one glutamic acid substitution in type I collagen has been fully reported. We describe here the clinical, biochemical, and molecular characterization of a girl with severe type III OI caused by a G76E substitution in COL1A1. This is the first delineation of a glutamic acid substitution in the alpha1(I) chain causing nonlethal osteogenesis imperfecta. The proband's fibroblast type I collagen chains and cyanogen bromide peptides were electrophoretically normal, while osteoblast collagen was slightly overmodified. This suggested a mutation near the N-terminal end of the collagen helix. A mismatch was detected by RNA:DNA hybrid analysis in cDNA coding for 106 amino acids at the N-terminal end of the helical region. Subclones of both alleles were sequenced and revealed a G --> A (c.761G > A) mutation causing an alpha1(I) G76E substitution in one allele. The presence of the mutation in the proband's leukocyte gDNA, and its absence in parental gDNA, was confirmed by Tsp509I digestion. The glutamic acid substitution alters the folding of the mutant collagen helices. Pericellular processing of type I collagen by the proband's fibroblasts yielded an earlier appearance of the pC-alpha1(I) form and of mature alpha chains as compared to control cell processing. Also, the presence of the glutamic acid substitution apparently exposes the adjacent Arg75 residue in the alpha1 chain. Trypsin digestion of proband fibroblast collagen resulted in shortened alpha1 chains, as confirmed by CNBr analysis. In addition, the Tm for mutant helices from fibroblasts and osteoblasts was decreased 2-4 degrees C versus controls, demonstrating a decrease in helix stability. These findings increase our understanding of the disruptive effect of glutamic acid substitutions in collagen.

Hammerhead ribozymes selectively suppress mutant type I collagen mRNA in osteogenesis imperfecta fibroblasts

Ribozymes are a promising agent for the gene therapy of dominant negative genetic disorders by allele-specific mRNA suppression. To test allele-specific mRNA suppression in cells, we used fibroblasts from a patient with osteogenesis imperfecta (OI). These cells contain a mutation in one alpha1(I) collagen allele which both causes the skeletal disorder and generates a novel ribozyme cleavage site. In a preliminary in vitro assay, ribozymes cleaved mutant RNA substrate whereas normal substrate was left intact. For the studies in cell culture we generated cell lines stably expressing active (AR) and inactive (IR) ribozymes targeted to mutant alpha1(I) collagen mRNA. Quantitative competitive RT-PCR analyses of type I collagen mRNA, normalized to beta-actin expression levels, revealed that the level of mutant alpha1(I) collagen mRNA was significantly decreased by approximately 50% in cells expressing AR. Normal alpha1(I) collagen mRNA showed no significant reduction when AR or IR was expressed from the pHbetaAPr-1-neo vector and a small (10-20%) but significant reduction when either ribozyme was expressed from the pCI.neo vector. In clonal lines derived from cells expressing AR the level of ribozyme expression correlated with the extent of reduction in the mutant:normal alpha1(I) mRNA ratio, ranging from 0.33 to 0.96. Stable expression of active ribozyme did not affect cell viability, as assessed by growth rates. Ribozyme cleavage of mutant mRNA results in a reduction in mutant type I collagen protein, as demonstrated by SDS-urea-PAGE. This is the first report of ribozymes causing specific suppression of an endogenous mutant mRNA in cells derived from a patient with a dominant negative genetic disorder.

Osteogenesis imperfecta: prospects for molecular therapeutics

Osteogenesis Imperfecta (OI) is a dominant negative disorder of connective tissue. OI patients present with bone fragility and skeletal deformity within a broad phenotypic range. Defects in the COL1A1 or COL1A2 genes, coding, respectively, for the alpha1 and alpha2 chains of type I collagen, are the causative mutations. Over 150 mutations have been characterized. Both quantitative defects, such as null COL1A1 alleles, and qualitative defects, such as glycine substitutions, exon skipping, deletions, and insertions, have been described in type I collagen. Quantitative and structural mutations are associated with the milder and more severe forms of OI, respectively. A more detailed relationship between genotype and phenotype is still incompletely understood; several models have been proposed and are being tested. Transgenic and knock-out murine models for OI have previously been created. We have recently generated a knock-in murine model (the Brittle mouse) carrying a typical glycine substitution in type I collagen. This mouse will permit a better understanding of OI pathophysiology and phenotypic variability. It will also be used for gene therapeutic approaches to OI, especially mutation suppression by hammerhead ribozymes. The present review will provide an update of OI clinical and molecular data and outline gene therapeutic approaches being tested on OI murine models for this disorder.

Calcium kinetics in children with osteogenesis imperfecta type III and IV: pre- and post-growth hormone therapy

Children with osteogenesis imperfecta (OI) type III and type IV were studied using a (42)Ca stable isotope technique. Serum dilution kinetics of (42)Ca were studied pre- and post-growth hormone (GH) treatment in 9 OI III (age range 5-9 years) and 8 OI IV patients (age range 5-12 years). Each subject was studied twice: at baseline and following GH therapy (range 1-1.5 years). Isotopic enrichments of (42)Ca were followed over 7 days using thermal ionization mass spectrometry. A binding site model, which describes reversible and irreversible binding of calcium (Ca) ions to postulated short- and long-term binding sites in bone, was used to analyze the kinetic data. In type III patients, GH treatment (1) increased the fraction of short-term binding sites, theta (0.777 +/- 0.112 versus 0.877 +/- 0.05, respectively; P = 0.034); (2) increased the apparent half-life of a Ca ion attached to the long-term binding site by 76% (P = 0. 009); (3) although not statistically significant (P = 0.098), a trend toward an increased growth rate was observed with increasing change in theta (Deltatheta); (4) patients experienced a 75% increase in growth rate during the first 6 months of treatment. In type IV patients, GH treatment increased the apparent half-life of a Ca ion attached to the long-term binding site by 83% (P = 0.048), however, no trend toward an increased growth rate was observed with increasing Deltatheta in these patients. These significant changes in Ca binding to bone may influence growth in type III patients.

Three novel type I collagen mutations in osteogenesis imperfecta type IV probands are associated with discrepancies between electrophoretic migration of osteoblast and fibroblast collagen

In three cases of type IV osteogenesis imperfecta (OI), we identified unique point mutations in type I collagen alpha1(I) cDNA. In two cases, the appearance of dimers indicated the presence of cysteine substitutions in the alpha1(I) protein chain. Cyanogen bromide digestion localized these cross-links to CB8 and 3, respectively. In the third case, the overmodification pattern of the CNBr peptides was compatible with a substitution in the aa 123-402 region of either type I collagen chain. We identified a unique point mutation in each proband, which resulted in substitutions for glycine residues in a 300-aa region of the alpha1(I) helix, specifically, Gly to Ala at codon 220 (GGT-->GCT), Gly to Cys at codon 349 (GGT-->TGT) and Gly to Cys at codon 523 (GGT-->TGT). We compared each proband's fibroblast and osteoblast collagen directly, as well as with fibroblast and osteoblast controls. For all cases, the OI osteoblast collagen was more electrophoretically delayed than OI fibroblast collagen. In the patient with G349C, OI fibroblast and osteoblast collagen synthesized in the presence of alpha,alpha'-dipyridyl co-migrated on gels, demonstrating that the electrophoretic discrepancy resulted from differences in post-translational modification. Melting temperature curves for stability of the collagen helix yielded an identical Tm for control fibroblast and osteoblast collagen (41.2 degrees C). By contrast, for collagen with the gly349-->cys substitution, the Tm of the fibroblast collagen was 1 degree C lower than the Tm of the osteoblast collagen. These data indicate that the metabolism of mutant collagen might be cell-specific and has significant implications for understanding the phenotype/genotype correlations and the pathophysiology of OI.

Use of the Cre/lox recombination system to develop a non-lethal knock-in murine model for osteogenesis imperfecta with an alpha1(I) G349C substitution. Variability in phenotype in BrtlIV mice

We utilized the Cre/lox recombination system to develop the first knock-in murine model for osteogenesis imperfecta (OI). The moderately severe OI phenotype was obtained from an alpha1(I) Gly(349) --> Cys substitution in type I collagen, reproducing the mutation in a type IV OI child. We introduced four single nucleotide (nt) changes into murine col1a1 exon 23: the disease causing G-->T transversion (nt 1546), an adjacent G-->T change (nt 1551) to generate a GUC ribozyme cleavage site, and two transversions (nt 1567 C-->A and nt 1569 C-->G) to cause a Leu --> Met substitution. We also introduced a 3.2-kilobase pair transcription/translation stop cassette in intron 22, flanked by directly repeating lox recombination sites. After homologous recombination in ES cells, two male chimeras were obtained. Chimeras were mated with transgenic females expressing Cre recombinase to remove the stop cassette from a portion of the progeny's cells. To generate mice with full expression of the Gly(349) --> Cys mutation, these offspring were then mated with wild-type females. Skeletal staining and bone histology of the F2 revealed a classical OI phenotype with deformity, fragility, osteoporosis and disorganized trabecular structure. We designate these mice BrtlIV (Brittle IV). BrtlIV mice have phenotypic variability ranging from perinatal lethality to long term survival with reproductive success. The phenotypic variability is not associated with differences in expression levels of the mutant allele in total RNA derived from tissue extracts. Expression of the mutant protein is also equivalent in different phenotypes. Thus, these mice are an excellent model for delineation of the modifying factors postulated to affect human OI phenotypes. In addition, we generated knock-in mice carrying an "intronic" inclusion by mating chimeras with wild-type females. Alternative splicing involving the stop cassette results in retention of non-collagenous sequences. These mice reproduce the lethal phenotype of similar human mutations and are designated BrtlII.

Effect of growth hormone treatment on calcium kinetics in patients with osteogenesis imperfecta type III and IV

Using a dual stable isotope technique, the effect of growth hormone (GH) on whole body calcium (Ca) metabolism was studied in children (ages 5-14 years) with type III (n = 9) and IV (n = 8) osteogenesis imperfecta. Each subject was studied twice: at baseline and following a GH (0.1-0.2 U/kg per day) treatment period of 1-1.5 years. Subjects were given 42Ca intravenously and 44Ca orally. The sera and urine 42Ca and 44Ca isotopic enrichments were followed over 7 days using thermal ionization mass spectrometry. The SAAM program was used to fit a three-compartment model to the tracer data. No significant differences were observed between: (1) children with type III and IV disease; or (2) baseline studies of boys and girls within each disease type. However, GH treatment significantly increased: (1) the exchangeable calcium pool (EP) in type III patients (2086 vs. 4422 mg/day, p = 0.02); and (2) the parameter associated with bone calcium accretion in type IV patients (Vo+: 973 vs. 1560 mg/day,p = 0.03) with boys responding with a significantly greater increase than girls (p = 0.008). Although not statistically significant, a trend toward an increase in Vo+ in type III patients and in EP in type IV was observed following treatment. Our observations imply that more Ca was available for bone mineralization following GH treatment in these subjects.

A patient with Ehlers-Danlos syndrome type VI is homozygous for a premature termination codon in exon 14 of the lysyl hydroxylase 1 gene

In the present study, we have characterized a patient with Ehlers-Danlos syndrome type VI (EDS VI) as homozygous for a pathogenetic mutation in the lysyl hydroxylase 1 (LH1) gene. This mutant allele contributes to very low levels of LH1 mRNA and severely diminished LH activity in his skin fibroblasts. The reduced hydroxylysine content of collagen was reflected in the increased electrophoretic mobility of the type I collagen alpha1 and alpha2 chains precipitated from cell and media samples of cultured patient fibroblasts. The homozygous mutation, a single base change of C1557 --> G which would convert a codon for tyrosine (TAC) at residue 511 to a stop codon (TAG) in exon 14 of the LH1 gene, was identified in full-length cDNAs for LH1 amplified from the patient's fibroblasts. We have demonstrated that the low level of LH activity measured in his fibroblasts may result from a minor processing pathway in which an in-frame skipping of exon 14 containing the mutation restores partial function of the enzyme. The mutation was confirmed in both alleles in genomic DNA from the proband and by the maternal inheritance of this mutation. The father's DNA was unavailable for analysis. The autosomal recessive nature of EDS VI was verified by the fact that the mother, who has one mutated and one normal allele, is clinically unaffected by this disorder. This mutation, which has been previously observed in another unrelated compound heterozygous patient, may prove to be a more widespread mutation for EDS VI.

Extension of phenotype associated with structural mutations in type I collagen: siblings with juvenile osteoporosis have an alpha2(I)Gly436 --> Arg substitution

Mutations in the type I collagen genes have been identified as the cause of all four types of osteogenesis imperfecta (OI). We now report a mutation that extends the phenotype associated with structural abnormalities in type I collagen. Two siblings presented with a history of back pain and were diagnosed with juvenile osteoporosis, based on clinical and radiological examination. Radiographs showed decreased lumbar bone density and multiple compression fractures throughout the thoracic and lumbar spines of both patients. One child has moderate short stature and mild neurosensory hearing loss. However, neither child has incurred the long bone fractures characteristic of OI. Protein studies demonstrated electrophoretically abnormal type I collagen in samples from both children. Enzymatic cleavage of RNA:RNA hybrids identified a mismatch in type I collagen alpha2 (COL1A2) mRNA. DNA sequencing of COL1A2 cDNA subclones defined the mismatch as a single-base mutation (1715G --> A) in both children. This mutation predicts the substitution of arginine for glycine at position 436 (G436R) in the helical domain of the alpha2(I) chain. Analysis of genomic DNA identified the mutation in the asymptomatic father, who is presumably a germ-line mosaic carrier. The presence of the same heterozygous mutation in two siblings strongly suggests that the probands display the full phenotype. Taken together, the clinical, biochemical, and molecular findings of this study extend the phenotype associated with type I collagen mutations to cases with only spine manifestations and variable short stature into adolescence.

Evaluation of oral problems in an osteogenesis imperfecta population

OBJECTIVE

The incidence of craniofacial and dental anomalies in children with the more severe nonlethal forms of osteogenesis imperfecta was evaluated.

STUDY DESIGN

The study evaluated 40 children (age range, 1-17.5 years) with types III and IV osteogenesis imperfecta. In each case, the dentition was evaluated for the presence of dentinogenesis imperfecta, attrition, and caries, as well as for radiographic appearance, dental development, and malocclusion.

RESULTS

The incidence of dentinogenesis imperfecta was greater than 80% in the primary dentition. Clinically, the color of the dentition was of predictive value in appropriate management of the primary dentition. Tooth discoloration and attrition did not occur to the same extent in the permanent dentition as in the primary dentition in either group. Class III dental malocclusion occurred in 70% to 80% of this osteogenesis imperfecta population, with a high incidence of anterior and posterior cross bites and open bites. A delay in dental development was observed in 21% of patients type III osteogenesis imperfecta, whereas accelerated development was noted in 23% of the patients with type IV. In addition, ectopic eruption occurred in 13 patients.

CONCLUSIONS

In addition to dentinogenesis imperfecta, significant oral problems occur in types III and IV osteogenesis imperfecta. Other features that impact the dental management of this population are highlighted.

An alpha2(I) glycine to aspartate substitution is responsible for the presence of a kink in type I collagen in a lethal case of osteogenesis imperfecta

Type I collagen synthesized by cultured skin fibroblasts was analyzed biochemically and molecularly to characterize the defect in a patient affected by lethal Osteogenesis Imperfecta. The SDS-Urea-PAGE of procollagen and collagen revealed a broad alpha1(I) band, a normal alpha2(I) and another alpha2(I) band migrating equidistant between alpha1 and alpha2. When synthesized in the presence of alphaalpha'-dipyridyl, an inhibitor of prolyl and lysyl hydroxylation, procollagen and collagen of media and cell layers contained both normal and slower alpha2(I), but only normal alpha1(I). The persistence of the two forms of alpha2(I) chains suggested a mutation in a COL1A2 gene. CNBr cleavage of collagen yielded overmodified alpha1(I) CB3 and CB7 peptides and delayed migration of the alpha2(I) CB3-5 peptide. A delayed CB3-5 was also found after alpha,alpha'-dipyridyl treatment. These data localized the mutation between aa 353 and 551 in alpha2(I) (CB3-5). Sequencing the subcloned alleles in this region revealed a G-->A transition at nt 1671 in one allele, changing Gly 421 to Asp in an alpha2(I) chain. The mutation was demonstrated to occur on the paternally derived allele, using a common C-->A polymorphism at alpha2(I) nt 1585 and by the presence of a rare variant, Arg618-->Gln (Phillips et al., 1990), in the paternal genomic DNA and the proband's mutant allele. Procollagen processing was normal. The Tm of the slow alpha2(I) collagen was 2 degrees C lower than the control, indicating decreased triple helix stability. Mutant collagen was incorporated in the extracellular matrix deposited by cultured fibroblasts. The dramatic delay in alpha2(I) electrophoretic mobility must be induced by the Gly-->Asp substitution, since the Arg-->Gln variant causes only mild electrophoretic delay. Substantial delay in gel mobility even in the absence of overmodification suggested the presence of a kink in the mutated alpha2(I) chains. Rotary shadowing electron microscopy of secreted fibroblast procollagen confirmed the presence of a kink in the region of the helix containing the glycine substitution. The kinking of the collagen helix occurs in the absence of dimer formation. Kinking may interfere with normal helix folding, as well as with the interactions of collagen fibrils with the collagenous and non-collagenous extracellular matrix proteins.

New genetic loci that control susceptibility and symptoms of experimental allergic encephalomyelitis in inbred mice

Experimental allergic encephalomyelitis (EAE), the principal animal model of multiple sclerosis, is a genetically determined phenotype. In this study, analyses of the cumulative disease frequencies in parental, F1 hybrid, and F2 mice, derived from the EAE-susceptible SJL/J strain and the EAE-resistant B10.S/DvTe strain, confirmed that susceptibility to EAE is not inherited as a simple Mendelian trait. Whole genome scanning, using 150 informative microsatellite markers and a panel of 291 affected and 390 unaffected F2 progeny, revealed significant linkage of EAE susceptibility to marker loci on chromosomes 7 (eae4) and 17, distal to H2 (eae5). Quantitative trait loci for EAE severity, duration, and onset were identified on chromosomes 11 (eae6, and eae7), 2 (eae8), 9 (eae9), and 3 (eae10). While each locus reported in this study is important in susceptibility or disease course, interactions between marker loci were not statistically significant in models of genetic control. One locus, eae7, colocalizes to the same region of chromosome II as Orch3 and Idd4, susceptibility loci in autoimmune orchitis and insulin-dependent diabetes mellitus, respectively. Importantly, eae5 and eae7 are syntenic with human chromosomes 6p21 and 17q22, respectively, two regions of potential significance recently identified in human multiple sclerosis genome scans.

Phenotypic comparison of an osteogenesis imperfecta type IV proband with a de novo alpha2(I) Gly922 --> Ser substitution in type I collagen and an unrelated patient with an identical mutation

We examined the type I collagen synthesized by cultured dermal fibroblasts from a patient affected with osteogenesis imperfecta (OI) type IV. Both normal and abnormal trimers were produced. The mutant collagen molecules were excessively modified intracellularly, had a melting temperature 4 degrees C lower than the control, were secreted at a reduced rate, and underwent delayed processing to mature alpha chains.Molecular investigations identified a G --> A transition in one COL1A2 allele, resulting in a Gly922 --> Ser substitution in the alpha2(I) chain. The proband's mutation was demonstrated to arise "de novo" by the absence of the mutant allele restriction enzyme pattern from parental genomic DNA.We analyzed the insoluble extracellular matrix deposited by long-term cultured fibroblasts from our patient and from a previously described unrelated individual who carries an identical substitution. In both cases, the mutant chain constituted 10-15% of the total alpha chains deposited.We also present here the first detailed comparison of phenotype between unrelated OI patients with an identical collagen mutation. These two patients are both Caucasian females, ages 8 and 9 years, each diagnosed as type IV OI by the Sillence classification. They have a similar phenotype including moderate skeletal fragility with several femur fractures, dentinogenesis imperfecta, wormian bone, and reduced height and weight. We conclude that this phenotype is related both to the location of this mutation and to the similar extent of matrix incorporation by the mutant chains. Molecular and biochemical studies of unrelated individuals with identical amino acid substitutions in type I collagen resulting in either similar or dissimilar clinical outcomes will make a significant contribution to identifying the factors involved in the modulation of the OI phenotype.

Cleavage of collagen RNA transcripts by hammerhead ribozymes in vitro is mutation-specific and shows competitive binding effects

We report here the in vitro use of hammerhead ribozymes as an approach to the gene therapy of osteogenesis imperfecta (OI). Our strategy for the treatment of this dominant genetic disorder is based on selective reduction of the level of the mRNA transcripts from the mutant allele. We studied the in vitro cleavage activity of five different hammerhead ribozymes targeted against synthetic transcripts of two naturally occurring human collagen mutations and against a point mutation introduced into a construct containing a portion of the mouse COL1A1 gene. This is the first demonstration that ribozyme cleavage is absolutely dependent on the presence of the ribozyme cleavage site introduced by the disease-causing mutation. Cleavage specificity and activity were unchanged when the cleavage site was located in transcripts of progressively longer length. Cleavage efficiency depended directly on the ratio of ribozyme/substrate, as well as on the time and temperature of incubation. We investigated the competitive effects of both total RNA and normal synthetic transcripts on ribozyme cleavage activity. The ribozyme was able to localize and cleave its specific target even in the presence of a vast excess of total RNA. However, cleavage efficiency was linearly inhibited by the presence of a non- cleavable competitor substrate which contained a ribozyme binding site identical to the site present in the cleavable target. Although this competition could be eliminated by introducing a mismatch into one ribozyme binding arm, the presence of the mismatch decreased ribozyme cleavage efficiency. The mutation- specificity of ribozyme cleavage demonstrated in this work provides support for in vivo studies aimed at ribozyme development as a treatment for dominant negative genetic disorders.

Prevention of experimental allergic encephalomyelitis by targeting nitric oxide and peroxynitrite: implications for the treatment of multiple sclerosis

In this study we provide further evidence associating activated cells of the monocyte lineage with the lesions of multiple sclerosis (MS). Using a combination of immunohistochemistry and reverse transcriptase-dependent in situ polymerase chain reaction analysis, we have identified monocytes expressing inducible nitric oxide synthase (iNOS) to be prevalent in the plaque areas of post mortem brain tissue from patients with MS. In addition, we have obtained evidence of the nitration of tyrosine residues in brain areas local to accumulations of iNOS-positive cells. In parallel studies we have assessed the effects of inhibitors of iNOS induction, as well as scavengers of nitric oxide and peroxynitrite in the experimental allergic encephalomyelitis model. Significant therapeutic effects were seen with the inhibitor of iNOS induction, tricyclodecan-9-xyl-xanthogenate, a nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, and a peroxynitrite scavenger, uric acid. In particular, treatment with high doses of uric acid virtually prevented clinical symptoms of the disease. Together with our demonstration of the presence of activated macrophages expressing high levels of iNOS and evidence of peroxynitrite formation in brain tissue from patients with MS, these findings are of importance in the development of approaches to treat this disease.

Ribozymes: structure, function, and potential therapy for dominant genetic disorders

Some dominant genetic disorders, viral processes and neoplastic disorders base their pathogenicity on the production of protein or proteins that negatively affect cellular metabolism or environment. Thus, the inhibition of the synthesis of those proteins should prevent the biological damage. A promising approach to decreasing the level of the abnormal protein(s) is represented by specific interference with gene expression at the level of mRNA. The specific suppression of the expression of an mRNA can be achieved by using ribozymes. Ribozymes are RNA molecules able to break and form covalent bonds within a nucleic acid molecule. These molecules, with even greater potential advantages than antisense oligodeoxynucleotides, are able to bind specifically and cleave an mRNA substrate. There are advantages to using ribozymes instead of antisense oligodeoxynucleotides. Ribozymes can inactivate the target RNA without relying on the host cell's machinery and they have the capacity to cleave more than one copy of the target RNA by dissociating from the cleavage products and binding to another target molecule. Most of the studies performed to date have described the use of ribozymes as therapeutic agents for viral and cancer diseases. However, some dominant genetic disorders may also benefit from this approach. This is the case for some connective tissue disorders such as osteogenesis imperfecta, Marfan syndrome and the craniosynostotic syndromes.

Alternative splicing in COL1A1 mRNA leads to a partial null allele and two In-frame forms with structural defects in non-lethal osteogenesis imperfecta

We have identified a novel multiexon genomic deletion in one COL1A1 collagen allele that results in three alternative forms of mutant mRNA. This mutation occurs in a 9-year-old girl and her father, both affected with severe type III osteogenesis imperfecta (OI). We previously reported detection of a mismatch in their alpha1(I) amino acids 558-861 region by RNA/RNA hybrid analysis (Grange, D. K., Gottesman, G. S., Lewis, M. B., and Marini, J. C. (1990) Nucleic Acids Res. 18, 4227-4236). Single Strand Conformational Polymorphism further localized the mRNA mutation to the amino acids 579-679 coding region. At the gene level, polymerase chain reaction (PCR) amplification of patient leukocyte DNA from the exon 33-38 region yielded the normal 1004-base pair (bp) fragment and an additional 442-bp fragment. Sequencing of the shorter genomic PCR product confirmed the presence of a 562-bp deletion, extending from the last 3 nucleotides (nt) of exon 34 to 156 nt from the 3'-end of intron 36. The genomic deletion was also detected in the clinically normal grandmother, who was confirmed to be a mosaic carrier. PCR amplification and RNase protection experiments were used to investigate the mRNA structure and occurrence of alternative splicing. One form of the mutant cDNA has a deletion with end points that are identical to the genomic deletion. This results in a combination deletion/insertion, with a deletion of amino acids 603-639 followed by an insertion of 156 nt from the 3'-end of intron 36. In addition, we found two alternatively spliced forms. One form uses a cryptic donor site in exon 34 and the exon 37 acceptor. The second form uses the normal exon 32 splice donor and exon 37 acceptor. Use of the cryptic donor results in a coding sequence that is out-of-frame. Both the retained intron form and the use of the exon 32 donor site result in coding sequences that are in-frame. This is the first report of a collagen defect in OI with alternative splicing generating both in-frame and out-of-frame forms of mRNA. Although the in-frame forms constitute more than 60% of the mRNA from the mutant allele, no mutant protein chain was identified. Collagen produced by cultured OI osteoblasts showed a significant increase in the relative amount of type III collagen but no mutant alpha1(I) chain.

Inhibitory effect of a CD4-CDR3 peptide analog on graft-versus-host disease across a major histocompatibility complex-haploidentical barrier

A structure-based designed peptide has been engineered to exhibit the same molecular surface as a portion of the CDR3-like region in domain 1 of the murine CD4 molecule. Earlier in vitro experiments indicated that this analog, known as rD-mPGPtide, inhibited T-cell proliferation in mixed lymphocyte reactions and blocked activation of both normal CD4+ T cells and T-cell lines after T-cell receptor triggering. In addition, rD-mPGPtide proved to be a potent inhibitor in vivo of CD4+ T-cell-mediated experimental allergic encephalomyelitis disease in the SJL mouse model. In this current report, we have evaluated the potential of rD-mPGPtide for suppressing the development of graft-versus-host disease (GVHD) in an irradiated major histocompatibility complex (MHC)-haploidentical murine bone marrow transplantation (BMT) model [(B6 x DBA/2)F1-->(B6 x CBA)F1 (950 cGy)]. Our results indicated that early administration of rD-mPGPtide was effective in the inhibition of alloreactive responses of the donor T cells against the host and thus delayed or prevented the onset of GVHD. The median survival time of animals treated with rD-mPGPtide was enhanced as much as four-fold with as little as a single dose of peptide at the time of transplant. Decreased alloreactivity was indicated by phenotypic and functional analysis of positively selected thoracic duct lymphocytes 4 days after transplant and by histopathological examination of skin and gastrointestinal tissue samples 4 weeks later. Therefore, the administration of a CD4-CDR3 peptide is an efficacious approach against the development of GVHD during allogeneic BMT.

A CD4-CDR3 peptide analog inhibits both primary and secondary autoreactive CD4+ T cell responses in experimental allergic encephalomyelitis

A structure-based design approach was used to develop a cyclized peptide analog of the murine CD4-CDR3-like region as a potential inhibitor of autoimmune CD4+ T cells responsible for the pathogenesis of experimental allergic encephalomyelitis (EAE). Our results indicate that this peptide, referred to as rD-mPGPtide, is able to significantly inhibit the clinical and pathologic symptoms of EAE in the SJL mouse model when administered on day 12 of induction. The optimum effective dosage range for the peptide, injected i.v., was between 0.125 and 0.5 mg and dosages of as high as 5 mg had no observable toxic effects. Treated mice had normal levels of lymphocytes less than 2 wk later and exhibited normal in vitro primary responses to alloantigen and secondary responses to keyhole limpet hemocyanin Ag. The specificity of the rD-mPGPtide treatment for autoreactive T cells was demonstrated by inhibiting proteolipid protein (p139-151)-induced EAE and finding that the lymph node T cells from these mice had suppressed responses to this Ag, but normal responses to alloantigen or other nominal Ag. Importantly, rD-mPGPtide was found to be effective on secondary T cell responses in an EAE rechallenge situation and was able to establish conditions for long-term resistance to further Ag exposure. Analysis of the cytokine profile of responding T cells during late effector stages of disease revealed that the levels of IFN-gamma and IL-4 are significantly reduced in rD-mPGPtide-treated mice. These results strongly suggest that the administration of a CD4-CDR3 peptide analog is an effective therapeutic approach for the inhibition of the CD4+ T cell-mediated autoimmune response in EAE.

A CD4-CDR3 peptide analog inhibits both primary and secondary autoreactive CD4+ T cell responses in experimental allergic encephalomyelitis

A structure-based design approach was used to develop a cyclized peptide analog of the murine CD4-CDR3-like region as a potential inhibitor of autoimmune CD4+ T cells responsible for the pathogenesis of experimental allergic encephalomyelitis (EAE). Our results indicate that this peptide, referred to as rD-mPGPtide, is able to significantly inhibit the clinical and pathologic symptoms of EAE in the SJL mouse model when administered on day 12 of induction. The optimum effective dosage range for the peptide, injected i.v., was between 0.125 and 0.5 mg and dosages of as high as 5 mg had no observable toxic effects. Treated mice had normal levels of lymphocytes less than 2 wk later and exhibited normal in vitro primary responses to alloantigen and secondary responses to keyhole limpet hemocyanin Ag. The specificity of the rD-mPGPtide treatment for autoreactive T cells was demonstrated by inhibiting proteolipid protein (p139-151)-induced EAE and finding that the lymph node T cells from these mice had suppressed responses to this Ag, but normal responses to alloantigen or other nominal Ag. Importantly, rD-mPGPtide was found to be effective on secondary T cell responses in an EAE rechallenge situation and was able to establish conditions for long-term resistance to further Ag exposure. Analysis of the cytokine profile of responding T cells during late effector stages of disease revealed that the levels of IFN-gamma and IL-4 are significantly reduced in rD-mPGPtide-treated mice. These results strongly suggest that the administration of a CD4-CDR3 peptide analog is an effective therapeutic approach for the inhibition of the CD4+ T cell-mediated autoimmune response in EAE.

Antisense oligodeoxynucleotides selectively suppress expression of the mutant alpha 2(I) collagen allele in type IV osteogenesis imperfecta fibroblasts. A molecular approach to therapeutics of dominant negative disorders

We are investigating the use of antisense oligodeoxynucleotides to selectively suppress expression of the mutant type I collagen allele in osteogenesis imperfecta (OI). In this report, we target a human collagen mutation in its natural cellular context. We used cultured fibroblasts from a case of type IV OI, in which the mutant alpha 2(I) allele produces mRNA with exon 16 deleted due to a point mutation in the splice donor site. Lipid-mediated transfection was used to deliver antisense, sense and missense phosphorothioates targeted to both the abnormal mRNA exon 15/17 junction and the nuclear level point mutation. Significant suppression of the mutant protein chain and mRNA was achieved with antisense oligonucleotide to both mRNA and nuclear levels. Mutant protein was suppressed to 44-47% and mutant alpha 2(I) mRNA to 37-43% of their levels in control cells, indicating decreased mRNA as the basis for suppression. Selectivity of mutant allele suppression was better with an mRNA target: suppression was sequence specific and normal mRNA was expressed at 79% of its level in untreated cells. With a nuclear target, significant suppression of mutant mRNA occurred not only with antisense and sense, but also with missense oligonucleotide, which suppressed mutant mRNA to 60% of its level in untreated cells. We also investigated the time course of suppression of protein and mRNA in response to a 4 h transfection of antisense oligonucleotide. From 24-72 h after transfection, mutant protein was suppressed to approximately 50% of its untreated level and suppression of mutant message was significantly greater than that of normal message. The suppression achieved in these studies is insufficient for clinical intervention, but our results provide support for further development of antisense therapy as an approach to the treatment of dominant negative disorders.

Neurologic profile in osteogenesis imperfecta

The clinically important neurlogic complications in 76 patients with OI seen at the NIH included brainstem compression from basilar invagination, skull fracture, and seizure disorders. Neuroimaging studies demonstrated sulcal prominence and ventriculomegaly consistent with communicating hydrocephalus in 17 patients. Basilar invagination was found in 8 individuals, all with clinically severe OI, and caused brain-stem compression in 3 patients. Head circumference growth showed abnormal kinetics with percentile crossing after fontanelle closure in 13 patients and absolute macrocephaly was present in 11 patients. Neurologic evaluation should be part of a team approach in the management of patients with severe OI types. Continued study of the underlying pathophysiology of neurologic features in OI is warranted.

A three-hour measurement to evaluate bone calcium turnover

It is well established that short-term clearance of an intravenous calcium load in vivo reflects bone uptake. Using results from isotope-dilution experiments with 42Ca, a 3-h test has been developed to measure a quantity, gamma, related to bone accretion. This test is proposed as a useful, clinically applicable measure of bone status. For early times, t, after a bolus of 42Ca, plasma tracer dilution was well approximated by t-gamma, where gamma is related to the fractional rate of loss of tracer, q, from blood into bone (1/q)(dq/dt) = -gamma/t). Gamma was evaluated from kinetic measurements on 91 normal female children, adolescents, and adult women in the age range 4-50 years. For t < or = 3 h, all clearance curves were well fit by a power function. Gamma was found to vary from 0.244 +/- 0.031 for adult premenopausal women (N = 22) to 0.392 +/- 0.056 for prepubertal children (N = 29). Using the Spearman rank-order correlation test, gamma was correlated with bone accretion measured from classic calcium kinetic studies with a correlation coefficient of 0.721, significant at p < 0.005. In those cases in which accretion and resorption remain tightly linked, gamma also provides information on the state of calcium loss from bone. Gamma was evaluated in 14 subjects with bone disease characterised by increased resorption (osteoporosis, Paget's disease) and in 27 subjects with decreased accretion (osteogenesis imperfecta, types I, III, IV; steroid-treated juvenile dermatomyositis). All subjects with Paget's disease and with osteoporosis showed increased gamma, consistent with high bone turnover. The osteoporotic patients furthermore exhibited gamma increasing monotonically by approximately 1% per year after age 55.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine aspects of growth deficiency in OI

Growth deficiency is the most common secondary feature of osteogenesis imperfecta. It is unrelated to fracture history and appears to be due to the growth failure of the defective bony matrix. There are characteristic growth curves for different types of OI. We have been investigating the endocrine features of this disorder, in which the skeletal target tissue synthesizes defective matrix. We review the results of our evaluation of the growth hormone axis in 28 children with short stature and OI and of our pilot study to stimulate OI bone to increased growth rates. Our current focus is on the effect of growth hormone treatment on linear growth, bony mineral and bony matrix in OI.

A rationally designed CD4 analogue inhibits experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is an acute inflammatory autoimmune disease of the central nervous system that can be elicited in rodents and is the major animal model for the study of multiple sclerosis (MS). The pathogenesis of both EAE and MS directly involves the CD4+ helper T-cell subset. Anti-CD4 monoclonal antibodies inhibit the development of EAE in rodents, and are currently being used in human clinical trials for MS. We report here that similar therapeutic effects can be achieved in mice using a small (rationally designed) synthetic analogue of the CD4 protein surface. It greatly inhibits both clinical incidence and severity of EAE with a single injection, but does so without depletion of the CD4+ subset and without the inherent immunogenicity of antibody. Furthermore, this analogue is capable of exerting its effects on disease even after the onset of symptoms.