Ablation of collagen XII disturbs joint extracellular matrix organization and causes patellar subluxation

Collagen XII, belonging to the fibril-associated collagens, is a homotrimeric secreted extracellular matrix (ECM) protein encoded by the COL12A1 gene. Mutations in the human COL12A1 gene cause an Ehlers-Danlos/myopathy overlap syndrome leading to skeletal abnormalities and muscle weakness. Here, we studied the role of collagen XII in joint pathophysiology by analyzing collagen XII deficient mice and human patients. We found that collagen XII is widely expressed across multiple connective tissue of the developing joint. Lack of collagen XII in mice destabilizes tendons and the femoral trochlear groove to induce patellar subluxation in the patellofemoral joint. These changes are associated with an ECM damage response in tendon and secondary quadriceps muscle degeneration. Moreover, patellar subluxation was also identified as a clinical feature of human patients with collagen XII deficiency. The results provide an explanation for joint hyperlaxity in mice and human patients with collagen XII deficiency.

Exploring complement-dependent cytotoxicity by rituximab isotypes in 2D and 3D-cultured B-cell lymphoma

Background

The therapeutic IgG1 anti-CD20 antibody, rituximab (RTX), has greatly improved prognosis of many B-cell malignancies. Despite its success, resistance has been reported and detailed knowledge of RTX mechanisms are lacking. Complement-dependent cytotoxicity (CDC) is one important mode of action of RTX. The aim of this study was to systematically evaluate factors influencing complement-mediated tumor cell killing by RTX.

Methods

Different RTX isotypes, IgG1, IgG3, IgA1 and IgA2 were evaluated and administered on four human CD20⁺ B-cell lymphoma cell lines, displaying diverse expression of CD20 and complement-regulatory protein CD59. Complement activation was assessed on lymphoma cells grown in 2 and 3-dimensional (3D) culture systems by trypan blue exclusion. CDC in 3D spheroids was additionally analyzed by Annexin V and propidium iodide staining by flow cytometry, and confocal imaging. Anti-CD59 antibody was used to evaluate influence of CD59 in RTX-mediated CDC responses. Statistical differences were determined by one-way ANOVA and Tukey post hoc test.

Results

We found that 3 out of 4 lymphomas were sensitive to RTX-mediated CDC when cultured in 2D, while 2 out of 4 when grown in 3D. RTX-IgG3 had the greatest CDC potential, followed by clinical standard RTX-IgG1 and RTX-IgA2, whereas RTX-IgA1 displayed no complement activation. Although the pattern of different RTX isotypes to induce CDC were similar in the sensitive lymphomas, the degree of cell killing differed. A greater CDC activity was seen in lymphoma cells with a higher CD20/CD59 expression ratio. These lymphomas were also sensitive to RTX when grown in 3D spheroids, although the CDC activity was substantially reduced compared to 2D cultures. Analysis of RTX-treated spheroids demonstrated apoptosis and necrosis essentially in the outer cell-layers. Neutralization of CD59 overcame resistance to RTX-mediated CDC in 2D-cultured lymphoma cells, but not in spheroids.

Conclusions

The results demonstrate that CDC outcome in CD20⁺ B-cell lymphoma is synergistically influenced by choice of RTX isotype, antigen density, tumor structure, and degree of CD59 expression. Assessment of tumor signatures, such as CD20/CD59 ratio, can be advantageous to predict CDC efficiency of RTX in vivo and may help to develop rational mAbs to raise response rates in patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09772-1.

Ablation of the miRNA cluster 24 in cartilage and osteoblasts impairs bone remodeling

MicroRNAs (miRNAs) post-transcriptionally regulate cartilage and bone development and function, however, only few miRNAs have been described to play a role for cartilage to bone transition in vivo. Previously, we showed that cartilage-specific deletion of the Mirc24 cluster in newborn male mice leads to impaired growth plate cartilage development due to increased RAF/MEK/ERK signaling and affects the stability of the cartilage extracellular matrix on account of decreased SOX6 and SOX9 and increased MMP13 levels. Here, we studied how Mirc24 cluster inactivation in cartilage and osteoblasts leads to an increased bone density associated with defects in collagen remodeling in trabecular bone. No changes in osteoblast distribution were observed, whereas the number of osteoclasts was reduced and TRAP activity in osteoclasts decreased. Surprisingly, an increased level of cluster-encoded miR-322 or miR-503 raises Rankl gene expression and inactivation of the cluster in chondrocytes reduces Rankl expression. These results suggest that the Mirc24 cluster regulates Rankl expression in chondrocytes at the chondro-osseous border, where the cluster is mainly expressed to modulate osteoclast formation, bone remodeling and bone integrity.

Pivotal Role of Tenascin-W (-N) in Postnatal Incisor Growth and Periodontal Ligament Remodeling

The continuously growing mouse incisor provides a fascinating model for studying stem cell regulation and organ renewal. In the incisor, epithelial and mesenchymal stem cells assure lifelong tooth growth. The epithelial stem cells reside in a niche known as the cervical loop. Mesenchymal stem cells are located in the nearby apical neurovascular bundle and in the neural plexus. So far, little is known about extracellular cues that are controlling incisor stem cell renewal and guidance. The extracellular matrix protein tenascin-W, also known as tenascin-N (TNN), is expressed in the mesenchyme of the pulp and of the periodontal ligament of the incisor, and is closely associated with collagen 3 fibers. Here, we report for the first time the phenotype of tenascin-W/TNN deficient mice, which in a C57BL/6N background exhibit a reduced body weight and lifespan. We found major defects in the alveolar bone and periodontal ligament of the growing rodent incisors, whereas molars were not affected. The alveolar bone around the incisor was replaced by a dense scar-like connective tissue, enriched with newly formed nerve fibers likely leading to periodontal pain, less food intake and reduced body weight. Using soft food to reduce mechanical load on the incisor partially rescued the phenotype. In situ hybridization and Gli1 reporter mouse experiments revealed decreased hedgehog signaling in the incisor mesenchymal stem cell compartment, which coordinates the development of mesenchymal stem cell niche. These results indicate that TNN deficiency in mice affects periodontal remodeling and increases nerve fiber branching. Through periodontal pain the food intake is reduced and the incisor renewal and the neurovascular sonic hedgehog secretion rate are reduced. In conclusion, tenascin-W/TNN seems to have a primary function in rapid periodontal tissue remodeling and a secondary function in mechanosensation.

The Matrilin-3 T298M mutation predisposes for post-traumatic osteoarthritis in a knock-in mouse model

OBJECTIVE

The human matrilin-3 T303M (in mouse T298M) mutation has been proposed to predispose for osteoarthritis, but due to the lack of an appropriate animal model this hypothesis could not be tested. This study was carried out to identify pathogenic mechanisms in a transgenic mouse line by which the mutation might contribute to disease development.

METHODS

A mouse line carrying the T298M point mutation in the Matn3 locus was generated and features of skeletal development in ageing animals were characterized by immunohistology, micro computed tomography, transmission electron microscopy and atomic force microscopy. The effect of transgenic matrilin-3 was also studied after surgically induced osteoarthritis.

RESULTS

The matrilin-3 T298M mutation influences endochondral ossification and leads to larger cartilage collagen fibril diameters. This in turn leads to an increased compressive stiffness of the articular cartilage, which, upon challenge, aggravates osteoarthritis development.

CONCLUSIONS

The mouse matrilin-3 T298M mutation causes a predisposition for post-traumatic osteoarthritis and the corresponding knock-in mouse line therefore represents a valid model for investigating the pathogenic mechanisms involved in osteoarthritis development.

Impact of knee joint loading on fragmentation of serum cartilage oligomeric matrix protein

The aim of the study was to examine the effect of mechanical knee joint loading on the fragmentation pattern of serum cartilage oligomeric matrix protein (COMP). Ten healthy men ran with knee orthoses that were passive or active (+30.9 N·m external flexion moments) on a treadmill (30 minute; v = 2.2 m/s). Lower-limb mechanics, serum COMP levels, and fragmentation patterns (baseline; 0, 0.5, 1, 2 hours postrunning) were analyzed. Running with active orthoses enhanced knee flexion moments, ankle dorsiflexion, and knee flexion angles (P < .05). There was an increase in serum COMP (+25%; pre: 8.9 ± 2.4 U/l; post: 10.7 ± 1.9 U/l, P = .001), COMP pentamer/tetramer (+88%; 1.88 ± 0.81, P = .007), trimer (+209%; 3.09 ± 2.65, P = .005), and monomer (+78%; 1.78 ± 0.85, P = .007) after running with passive orthoses and in serum COMP (+41%; pre: 8.5 ± 2.7 U/l; post: 11.3 ± 2.1 U/l, P < .001), COMP pentamer/tetramer (+57%; 1.57 ± 0.39, P = .007), trimer (+86%; 1.86 ± 0.47, P = .005), and monomer (+19%; 1.19 ± 0.34, P = .114) after running with active orthoses. Increased fragmentation might indicate COMP release from cartilage while running. Interestingly, 0.5 h up to 2 hours after running with passive orthoses, trimer (0.5 hour: 2.73 ± 3.40, P = .029; 2 hours: 2.33 ± 2.88, P = .037), and monomer (0.5 hour: 2.23 ± 2.33, P = .007; 1 hour: 2.55 ± 1.96, P = .012; 2 hours: 2.65 ± 2.50, P = .009) increased while after running with active orthoses, pentamer/tetramer (1 hour: 0.79 ± 0.28, P = .029), and trimer (1 hour: 0.63 ± 0.14, P = .005; 2 hours: 0.68 ± 0.34, P = .047) decreased. It seems that COMP degradation and clearance vary depending on joint loading characteristics.

COMP in the Infrapatellar Fat Pad-Results of a Prospective Histological, Immunohistological, and Biochemical Case-Control Study

Knee osteoarthritis (OA) involves several structures and molecules in the joint, which interact in a pathophysiological process. One of these molecules is the cartilage oligomeric matrix protein (COMP). Elevated COMP levels in the synovial fluid as well as in the serum have been described in OA patients. However, this has not been described in the infrapatellar fat pad (IPFP) tissue before. In this prospective trial, we collected 14 IPFPs from patients with high-grade OA (mean age 63.8 ± 17.6 years) who underwent total knee replacement (OA group) and from 11 healthy patients (mean age 33.7 ± 14.8 years) who underwent anterior cruciate ligament reconstruction (control group). The presence of macrophages (CD68 and CD206) and proinflammatory cytokines (interleukin 1β [IL-1β] and IL-6) was analyzed. Histological and immunohistological examinations as well as immunoblotting analysis for COMP, leptin, and matrix-metalloproteinase-3 were performed. The IPFPs of both the OA and control group consisted of adipose tissue and fibrous tissue, and the fibrous tissue showed higher score values than the adipose tissue for COMP staining (intensity as well as stained area) in both groups. Although COMP could be detected in most samples, leptin expression was found only in single specimens. COMP could be detected mostly in the fibrous tissue portion of the IPFP. We speculate that it is involved in a remodeling process taking place in the IPFP during OA. Presence of leptin was irregular in immunohistology, and the control group showed higher scores in case of presence. Interestingly, immunoblotting could detect leptin in all analyzed samples. © 2019 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society J Orthop Res 38:747-758, 2020.

Mice Lacking the Matrilin Family of Extracellular Matrix Proteins Develop Mild Skeletal Abnormalities and Are Susceptible to Age-Associated Osteoarthritis

Matrilins (MATN1, MATN2, MATN3 and MATN4) are adaptor proteins of the cartilage extracellular matrix (ECM), which bridge the collagen II and proteoglycan networks. In humans, dominant-negative mutations in MATN3 lead to various forms of mild chondrodysplasias. However, single or double matrilin knockout mice generated previously in our laboratory do not show an overt skeletal phenotype, suggesting compensation among the matrilin family members. The aim of our study was to establish a mouse line, which lacks all four matrilins and analyze the consequence of matrilin deficiency on endochondral bone formation and cartilage function. Matn1-4^−/− mice were viable and fertile, and showed a lumbosacral transition phenotype characterized by the sacralization of the sixth lumbar vertebra. The development of the appendicular skeleton, the structure of the growth plate, chondrocyte differentiation, proliferation, and survival were normal in mutant mice. Biochemical analysis of knee cartilage demonstrated moderate alterations in the extractability of the binding partners of matrilins in Matn1-4^−/− mice. Atomic force microscopy (AFM) revealed comparable compressive stiffness but higher collagen fiber diameters in the growth plate cartilage of quadruple mutant compared to wild-type mice. Importantly, Matn1-4^−/− mice developed more severe spontaneous osteoarthritis at the age of 18 months, which was accompanied by changes in the biomechanical properties of the articular cartilage. Interestingly, Matn4^−/− mice also developed age-associated osteoarthritis suggesting a crucial role of MATN4 in maintaining the stability of the articular cartilage. Collectively, our data provide evidence that matrilins are important to protect articular cartilage from deterioration and are involved in the specification of the vertebral column.

Respiratory chain inactivation links cartilage-mediated growth retardation to mitochondrial diseases

Children with mitochondrial diseases often present with slow growth and short stature, but the underlying mechanism remains unclear. In this study, Holzer et al. provide in vivo evidence that mitochondrial respiratory chain dysfunction induces cartilage degeneration coincident with altered metabolism, impaired extracellular matrix formation, and cell death at the cartilage–bone junction.

In childhood, skeletal growth is driven by transient expansion of cartilage in the growth plate. The common belief is that energy production in this hypoxic tissue mainly relies on anaerobic glycolysis and not on mitochondrial respiratory chain (RC) activity. However, children with mitochondrial diseases causing RC dysfunction often present with short stature, which indicates that RC activity may be essential for cartilage-mediated skeletal growth. To elucidate the role of the mitochondrial RC in cartilage growth and pathology, we generated mice with impaired RC function in cartilage. These mice develop normally until birth, but their later growth is retarded. A detailed molecular analysis revealed that metabolic signaling and extracellular matrix formation is disturbed and induces cell death at the cartilage–bone junction to cause a chondrodysplasia-like phenotype. Hence, the results demonstrate the overall importance of the metabolic switch from fetal glycolysis to postnatal RC activation in growth plate cartilage and explain why RC dysfunction can cause short stature in children with mitochondrial diseases.

Plastin 3 influences bone homeostasis through regulation of osteoclast activity

Over 200 million people suffer from osteoporosis worldwide, one third of which will develop osteoporotic bone fractures. Unfortunately, no effective cure exists. Mutations in plastin 3 (PLS3), an F-actin binding and bundling protein, cause X-linked primary osteoporosis in men and predisposition to osteoporosis in postmenopausal women. Moreover, the strongest association so far for osteoporosis in elderly women after menopause was connected to a rare SNP in PLS3, indicating a possible role of PLS3 in complex osteoporosis as well. Interestingly, 5% of the general population are overexpressing PLS3, with yet unknown consequences. Here, we studied ubiquitous Pls3 knockout and PLS3 overexpression in mice and demonstrate that both conditions influence bone remodeling and structure: while Pls3 knockout mice exhibit osteoporosis, PLS3 overexpressing mice show thickening of cortical bone and increased bone strength. We show that unbalanced PLS3 levels affect osteoclast development and function, by misregulating the NFκB pathway. We found upregulation of RELA (NFκB subunit p65) in PLS3 overexpressing mice-known to stimulate osteoclastogenesis-but strikingly reduced osteoclast resorption. We identify NFκB repressing factor (NKRF) as a novel PLS3 interactor, which increasingly translocates to the nucleus when PLS3 is overexpressed. We show that NKRF binds to the NFκB downstream target and master regulator of osteoclastogenesis nuclear factor of activated T cells 1 (Nfatc1), thereby reducing its transcription and suppressing osteoclast function. We found the opposite in Pls3 knockout osteoclasts, where decreased nuclear NKRF augmented Nfatc1 transcription, causing osteoporosis. Regulation of osteoclastogenesis and bone remodeling via the PLS3-NKRF-NFκB-NFATC1 axis unveils a novel possibility to counteract osteoporosis.

Impact of Arginine to Cysteine Mutations in Collagen II on Protein Secretion and Cell Survival

Inherited point mutations in collagen II in humans affecting mainly cartilage are broadly classified as chondrodysplasias. Most mutations occur in the glycine (Gly) of the Gly-X-Y repeats leading to destabilization of the triple helix. Arginine to cysteine substitutions that occur at either the X or Y position within the Gly-X-Y cause different phenotypes like Stickler syndrome and congenital spondyloepiphyseal dysplasia (SEDC). We investigated the consequences of arginine to cysteine substitutions (X or Y position within the Gly-X-Y) towards the N and C terminus of the triple helix. Protein expression and its secretion trafficking were analyzed. Substitutions R75C, R134C and R704C did not alter the thermal stability with respect to wild type; R740C and R789C proteins displayed significantly reduced melting temperatures (T_m) affecting thermal stability. Additionally, R740C and R789C were susceptible to proteases; in cell culture, R789C protein was further cleaved by matrix metalloproteinases (MMPs) resulting in expression of only a truncated fragment affecting its secretion and intracellular retention. Retention of misfolded R740C and R789C proteins triggered an ER stress response leading to apoptosis of the expressing cells. Arginine to cysteine mutations towards the C-terminus of the triple helix had a deleterious effect, whereas mutations towards the N-terminus of the triple helix (R75C and R134C) and R704C had less impact.

miR-322 stabilizes MEK1 expression to inhibit RAF/MEK/ERK pathway activation in cartilage

Cartilage originates from mesenchymal cell condensations that differentiate into chondrocytes of transient growth plate cartilage or permanent cartilage of the articular joint surface and trachea. MicroRNAs fine-tune the activation of entire signaling networks and thereby modulate complex cellular responses, but so far only limited data are available on miRNAs that regulate cartilage development. Here, we characterize a miRNA that promotes the biosynthesis of a key component in the RAF/MEK/ERK pathway in cartilage. Specifically, by transcriptome profiling we identified miR-322 to be upregulated during chondrocyte differentiation. Among the various miR-322 target genes in the RAF/MEK/ERK pathway, only Mek1 was identified as a regulated target in chondrocytes. Surprisingly, an increased concentration of miR-322 stabilizes Mek1 mRNA to raise protein levels and dampen ERK1/2 phosphorylation, while cartilage-specific inactivation of miR322 in mice linked the loss of miR-322 to decreased MEK1 levels and to increased RAF/MEK/ERK pathway activation. Such mice died perinatally due to tracheal growth restriction and respiratory failure. Hence, a single miRNA can stimulate the production of an inhibitory component of a central signaling pathway to impair cartilage development.

Extracellular Distribution of Collagen II and Perifibrillar Adapter Proteins in Healthy and Osteoarthritic Human Knee Joint Cartilage

Perifibrillar adapter proteins, interconnecting collagen fibrils, and linking the collagen network with the aggrecan matrix seem to play a crucial role in the pathogenesis of osteoarthritis (OA). Therefore, we examined immunohistochemically the extracellular distribution of collagen II and the main perifibrillar adapter proteins-collagen IX, decorin, cartilage oligomeric matrix protein (COMP), and matrilin-3-in human samples of healthy (n=4) and OA (n=42) knee joint cartilage. Histopathology assessment was performed using an OA score. Staining patterns were evaluated in relation to the disease stage. The perifibrillar adapter proteins were uniformly distributed in the upper zones of healthy cartilage. In moderate OA (n=8; score 14.3 ± 4.7), all proteins analyzed were locally absent in the fibrillated area or the superficial and upper mid zone. In advanced OA (n=20; score 18.9 ± 5.3), they were uniformly distributed in these zones and accumulated pericellularly. Perifibrillar adapter proteins are important for the stabilization of the collagen network in the upper zones of healthy cartilage. Their degradation might be a critical event in early OA. In advanced OA, there are indications for an increased synthesis in an attempt to regenerate the lost tissue and to protect the remaining cartilage from further destruction.

Collagen II regulates chondroycte integrin expression profile and differentiation

Collagen II is the major fibril-forming collagen in cartilage. Complete absence of collagen II in mice is not compatible with life and in humans mutations in the COL2A1 gene lead to osteochondrodysplasias with diverse phenotypes. However, mechanistic studies on how chondrocytes respond to a lack of collagen II in their extracellular matrix are limited. Primary mouse chondrocytes were isolated from knee joints of newborn mice and transfected with siRNA targeting Col2α1 to suppress collagen II expression. The expression of integrin receptors and matrix proteins was investigated by RT-PCR and immunoblots. The localization of matrix components was evaluated by immunostaining. Signaling pathways and the differentiation state of chondrocytes was monitored by RT-PCR and flow cytometry. We demonstrate that in the absence of collagen II chondrocytes start to produce collagen I. Some binding partners of collagen II are partially lost from the matrix while other proteins, e.g. COMP, were still found associated with the newly formed collagen network. The lack of collagen II induced changes in the expression profile of integrins. Further, we detected alterations in the Indian hedgehog/parathyroid hormone-related protein (Ihh/PTHrP) pathway that were accompanied by changes in the differentiation state of chondrocytes. Collagen II seems not to be essential for chondrocyte survival in culture but it plays an important role in maintaining chondrocyte differentiation. We suggest that a crosstalk between extracellular matrix and cells via integrins and the Ihh/PTHrP pathway is involved in regulating the differentiation state of chondrocytes.

Moderate cyclic tensile strain alters the assembly of cartilage extracellular matrix proteins in vitro

Mechanical loading influences the structural and mechanical properties of articular cartilage. The cartilage matrix protein collagen II essentially determines the tensile properties of the tissue and is adapted in response to loading. The collagen II network is stabilized by the collagen II-binding cartilage oligomeric matrix protein (COMP), collagen IX, and matrilin-3. However, the effect of mechanical loading on these extracellular matrix proteins is not yet understood. Therefore, the aim of this study was to investigate if and how chondrocytes assemble the extracellular matrix proteins collagen II, COMP, collagen IX, and matrilin-3 in response to mechanical loading. Primary murine chondrocytes were applied to cyclic tensile strain (6%, 0.5 Hz, 30 min per day at three consecutive days). The localization of collagen II, COMP, collagen IX, and matrilin-3 in loaded and unloaded cells was determined by immunofluorescence staining. The messenger ribo nucleic acid (mRNA) expression levels and synthesis of the proteins were analyzed using reverse transcription-polymerase chain reaction (RT-PCR) and western blots. Immunofluorescence staining demonstrated that the pattern of collagen II distribution was altered by loading. In loaded chondrocytes, collagen II containing fibrils appeared thicker and strongly co-stained for COMP and collagen IX, whereas the collagen network from unloaded cells was more diffuse and showed minor costaining. Further, the applied load led to a higher amount of COMP in the matrix, determined by western blot analysis. Our results show that moderate cyclic tensile strain altered the assembly of the extracellular collagen network. However, changes in protein amount were only observed for COMP, but not for collagen II, collagen IX, or matrilin-3. The data suggest that the adaptation to mechanical loading is not always the result of changes in RNA and/or protein expression but might also be the result of changes in matrix assembly and structure.

First result from the Alpha Magnetic Spectrometer on the International Space Station: precision measurement of the positron fraction in primary cosmic rays of 0.5-350 GeV

A precision measurement by the Alpha Magnetic Spectrometer on the International Space Station of the positron fraction in primary cosmic rays in the energy range from 0.5 to 350 GeV based on 6.8 × 10(6) positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to ∼ 250  GeV, but, from 20 to 250 GeV, the slope decreases by an order of magnitude. The positron fraction spectrum shows no fine structure, and the positron to electron ratio shows no observable anisotropy. Together, these features show the existence of new physical phenomena.

Effect of different running modes on the morphological, biochemical, and mechanical properties of articular cartilage

Mechanical loading plays an important role not solely in cartilage development, but also in cartilage degeneration. Its adaptation behavior to mechanical loading has not been clearly delineated. The aim of the study was to examine the effect of different running modes (with different muscle contraction types) on morphological, biochemical, and mechanical properties of articular cartilage in the knee of growing rats. Thirty-six female Sprague-Dawley rats were randomly assigned into a nonactive age-matched control (AMC), level (LEVEL), and 20° downhill (DOWN) running group (n = 12 each). Running groups were trained on a treadmill for 30 min/day, 5 days/week for 6 weeks. Immunohistochemical staining and analysis of expression for collagen II, collagen IX, cartilage oligomeric matrix protein (COMP), and matrilin-3, histomorphometry of femoral cartilage height and femoral COMP staining height, and indentation testing of tibial articular cartilage were performed. Rats subjected to downhill running showed a significantly (P = 0.015) higher COMP staining height and a tendentially (P = 0.084) higher cartilage height in the high-weight bearing area of femoral articular cartilage. Cartilage thickness, mechanical properties, and expression of cartilage network proteins in tibial cartilage remained unaffected by different running modes. Our data suggest that joint loading induced by eccentric muscle contractions during downhill running may lead to a site-specific adaptation.

Mutations in the rpoH (htpR) gene of Escherichia coli K-12 phenotypically suppress a temperature-sensitive mutant defective in the sigma 70 subunit of RNA polymerase

Escherichia coli K-12 strain 285c contains a mutation in rpoD, the gene encoding the sigma subunit of RNA polymerase. The 70-kilodalton sigma polypeptide encoded by this allele is unstable, and this instability leads to temperature-sensitive growth. We describe the isolation and characterization of four temperature-resistant pseudorevertants of 285c that can grow at high temperature. Each of these revertants increased the stability of the sigma 70 mutant protein. The map position of the suppressor mutations was close to that of the rpoH (htpR) gene. A multicopy plasmid containing the intact rpoH gene restored the temperature-sensitive phenotype. Marker rescue experiments established the positions of three of the alleles within the rpoH gene. One mutation has been sequenced and causes a leucine-to-tryptophan change 7 amino acids from the carboxyl terminus of the rpoH gene product.

Calcium hydroxide pulpotomy for primary teeth: a clinical study

Calcium hydroxide pulpotomies were performed in 17 carious primary mandibular molars. Variables in the pulpotomy procedure were recognized and controlled in an attempt to obtain a more favorable result or end product. The effects of two methods of hemorrhage control were also evaluated. The duration of treatment for the study ranged from three to nine months. Treatment was clinically successful for all 17 teeth. The radiographic evaluations were more favorable for the experimental group than for the control group. Treatment was radiographically successful for 15 teeth, questionable for one tooth, and unsuccessful for one other tooth. The results of this study suggest that the aluminum chloride-calcium hydroxide pulpotomy may be a viable alternative to formocresol pulpotomies in the primary dentition. Although these findings encourage continued research, including a long-term follow-up, a histologic study is indicated.