Transcriptomic analyses of joint tissues during osteoarthritis development in a rat model reveal dysregulated mechanotransduction and extracellular matrix pathways

OBJECTIVE

Transcriptomic changes in joint tissues during the development of osteoarthritis (OA) are of interest for the discovery of biomarkers and mechanisms of disease. The objective of this study was to use the rat medial meniscus transection (MMT) model to discover stage and tissue-specific transcriptomic changes.

DESIGN

Sham or MMT surgeries were performed in mature rats. Cartilage, menisci and synovium were scored for histopathological changes at 2, 4 and 6 weeks post-surgery and processed for RNA-sequencing. Differentially expressed genes (DEG) were used to identify pathways and mechanisms. Published transcriptomic datasets from animal models and human OA were used to confirm and extend present findings.

RESULTS

The total number of DEGs was already high at 2 weeks (723 in meniscus), followed by cartilage (259) and synovium (42) and declined to varying degrees in meniscus and synovium but increased in cartilage at 6 weeks. The most upregulated genes included tenascins. The 'response to mechanical stimulus' and extracellular matrix-related pathways were enriched in both cartilage and meniscus. Pathways that were enriched in synovium at 4 weeks indicate processes related to synovial hyperplasia and fibrosis. Synovium also showed upregulation of IL-11 and several MMPs. The mechanical stimulus pathway included upregulation of the mechanoreceptors PIEZO1, PIEZO2 and TRPV4 and nerve growth factor. Analysis of data from prior RNA-sequencing studies of animal models and human OA support these findings.

CONCLUSION

These results indicate several shared pathways that are affected during OA in cartilage and meniscus and support the role of mechanotransduction and other pathways in OA pathogenesis.

Challenges and opportunities in the investigation of unexplained intellectual disability using family-based whole-exome sequencing

Intellectual disability (ID), characterized by an intellectual performance of at least 2 SD (standard deviations) below average is a frequent, lifelong disorder with a prevalence of 2-3%. Today, only for at most half of patients a diagnosis is made. Knowing the cause of the ID is important for patients and their relatives, as it allows for appropriate medical care, prognosis on further development of the disorder, familial counselling or access to support groups. Whole-exome sequencing (WES) now offers the possibility to identify the genetic cause for patients for which all previously available genetic tests, including karyotyping, specific gene analysis, or microarray analysis did not reveal causative abnormalities. However, data analysis of WES experiments is challenging. Here we present an analysis workflow implementable in any laboratory, requiring no bioinformatics knowledge. We demonstrated its feasibility on a cohort of 10 patients, in which we found a conclusive diagnosis in 3 and a likely diagnosis in 2 more patients. Of the three conclusive diagnoses, one was a clinically suspected mutation missed by Sanger sequencing, and one was an atypical presentation of a known monogenic disorder, highlighting two essential strengths of WES-based diagnostics.

A DNA enzyme with N-glycosylase activity

In vitro evolution was used to develop a DNA enzyme that catalyzes the site-specific depurination of DNA with a catalytic rate enhancement of about 10(6)-fold. The reaction involves hydrolysis of the N-glycosidic bond of a particular deoxyguanosine residue, leading to DNA strand scission at the apurinic site. The DNA enzyme contains 93 nucleotides and is structurally complex. It has an absolute requirement for a divalent metal cation and exhibits optimal activity at about pH 5. The mechanism of the reaction was confirmed by analysis of the cleavage products by using HPLC and mass spectrometry. The isolation and characterization of an N-glycosylase DNA enzyme demonstrates that single-stranded DNA, like RNA and proteins, can form a complex tertiary structure and catalyze a difficult biochemical transformation. This DNA enzyme provides a new approach for the site-specific cleavage of DNA molecules.

Caged single and double strand breaks

Ionizing radiation and radiomimetic drugs such as bleomycin, calichieamycin, neocarzinostatin chromophore, and other synthetic agents can produce both single and double strand breaks in DNA. The ability to study the structure-activity relationships of single and double-strand break repair, lethality, and mutagenesis in vivo is complicated by the numerous types and sites of DNA cleavage products that can be induced by such agents. The ability to "cage" such breaks in DNA might help to further such studies and additionally afford a mechanism for activating and deactivating nucleic acid based drugs and probes. The major type of single strand break induced by ionizing radiation is a 3'- and 5'-phosphate terminated single nucleotide gap. Previously, a caged strand break of this type had been developed that was designed to produce the 5'-phosphate directly upon irradiation with 366 nm light, and the 3'-phosphate by a subsequent beta-elimination reaction [Ordoukhanian, P., and Taylor, J.-S. (1995) J. Am. Chem. Soc. 117, 9570]. Unfortunately, the release of the 3'-phosphate group was quite slow at pH 7. To circumvent this problem, a second caged strand break has been developed that produces the 3'-phosphate directly upon irradiation, and the 5'-phosphate by a subsequent beta-elimination reaction. When this caged strand break was used in tandem with the previous caged strand break, 5'- and 3'-phosphate terminated gaps could be directly produced by irradiation with 366 nm light. These caged single strand breaks were also incorporated in tandem into hairpin substrates to demonstrate that they could be used to cage double strand breaks. These caged single strand breaks should be generally useful for generating site-specific DNA single and double strand breaks and gaps, using wavelengths and doses of light that are nondetrimental to biological systems. Because the position of the single strand break can be varied, it should now be possible to examine the effect of the sequence context and cleavage pattern of single and double strand breaks on the lethality and mutagenicity of this important class of DNA damage.

A molecular description of the evolution of resistance

BACKGROUND

In vitro evolution has been used to obtain nucleic acid molecules with interesting functional properties. The evolution process usually is carried out in a stepwise manner, involving successive rounds of selection, amplification and mutation. Recently, a continuous in vitro evolution system was devised for RNAs that catalyze the ligation of oligonucleotide substrates, allowing the evolution of catalytic function to be studied in real time.

RESULTS

Continuous in vitro evolution of an RNA ligase ribozyme was carried out in the presence of a DNA enzyme that was capable of cleaving, and thereby inactivating, the ribozyme. The DNA concentration was increased steadily over 33.5 hours of evolution, reaching a final concentration that would have been sufficient to inactivate the starting population in one second. The evolved population of ribozymes developed resistance to the DNA enzyme, reducing their vulnerability to cleavage by 2000-fold but retaining their own catalytic function. Based on sequencing and kinetic analysis of the ribozymes, two mechanisms are proposed for this resistance. One involves three nucleotide substitutions, together with two compensatory mutations, that alter the site at which the DNA enzyme binds the ribozyme. The other involves enhancement of the ribozyme's ability to bind its own substrate in a way that protects it from cleavage by the DNA enzyme.

CONCLUSIONS

The ability to direct the evolution of an enzyme's biochemical properties in response to the behavior of another macromolecule provides insight into the evolution of resistance and may be useful in developing enzymes with novel or enhanced function.

Solid phase-supported thymine dimers for the construction of dimer-containing DNA by combined chemical and enzymatic synthesis: a potentially general method for the efficient incorporation of modified nucleotides into DNA

The ability to study the structure-activity relationships of the cis-syn thymine dimer, the major photoproduct of DNA, has been greatly aided by the availability of a building block suitable for its sequence-specific incorporation into oligonucleotides by standard automated DNA synthesis. Unfortunately, its usefulness is compromised by the fact that it takes six steps to synthesize in low overall yield and, as with all phosphoramidite building blocks, has to be used in great excess over the support in standard automated synthesis. To extend the usefulness of this building block, we have directly coupled it to standard A, C, G and T long chain alkylamine-linked controlled pore glass supports to yield a solid phase-supported dimer. We then demonstrate that 13mers containing a 3'-terminal d(T[cis-syn]TN) group synthesized with this support at 0.2 micromol scale can be efficiently incorporated into longer oligonucleotides by both primer extension with 3'-->5'exonuclease-deficient Klenow fragment or T4 polymerase and dNTPs or by enzymatic ligation with T4 DNA ligase to another oligonucleotide opposite a complementary template. The site specificity and integrity of the cis-syn thymine dimer after both primer extension and ligation was confirmed by cis-syn dimer-specific cleavage with T4 denV endonuclease V. This general approach should be applicable to the synthesis of many types of site-specific nucleic acid modifications and would be of particular use for those for which the required building blocks are expensive or difficult to make.