ERK1/2-mediated activation of DRP1 regulates mitochondrial dynamics and apoptosis in chondrocytes.

OBJECTIVE: To determine the Dynamin-related protein 1 (DRP1) regulation of mitochondrial fission in chondrocytes under pathological conditions, an area which is underexplored in osteoarthritis pathogenesis. DESIGN: DRP1 protein expression was determined by immunohistochemistry (IHC) or immunofluorescence (IF) staining of cartilage sections. IL-1ß-induced DRP1 mRNA expression in chondrocytes was quantified by qPCR and protein expression by immunoblotting. Mitochondrial fragmentation in chondrocytes was visualized by MitoTracker staining or IF staining of mitochondrial marker proteins or by transient expression of mitoDsRed. Mitochondrial reactive oxygen species (ROS) levels were determined by MitoSOX staining. Apoptosis was determined by lactate dehydrogenase (LDH) release assay, Caspase 3/7 activity assay, propidium iodide (PI), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and IF staining of cleaved caspase 3. Cytochrome c release was determined by confocal microscopy. Surgical destabilization of the medial meniscus (DMM) was used to induce osteoarthritis (OA) in mice. RESULTS: Expression of DRP1 and mitochondrial damage was high in human OA cartilage and in the joints of mice subjected to DMM surgery which also showed increased chondrocytes apoptosis. IL-1ß-induced mitochondrial network fragmentation and chondrocyte apoptosis via modulation of DRP1 expression and activity and induce apoptosis via Bax-mediated release of Cytochrome c. Pharmacological inhibition of DRP1 activity by Mdivi-1 blocked IL-1ß-induced mitochondrial damage and apoptosis in chondrocytes. Additionally, IL-1ß-induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) is crucial for DRP1 activation and induction of mitochondrial network fragmentation in chondrocytes as these were blocked by inhibiting ERK1/2 activation. CONCLUSIONS: These findings demonstrate that ERK1/2 is a critical player in DRP1-mediated induction of mitochondrial fission and apoptosis in IL-1ß-stimulated chondrocytes.

Lysosomal dysfunction in osteoarthritis and aged cartilage triggers apoptosis in chondrocytes through BAX mediated release of Cytochrome c.

OBJECTIVE: Lysosomes are the major catabolic organelle of the cell and regulate the macromolecular and organelle turnover and programmed cell death. Here, we investigated the lysosome dysfunction in cartilage and its role in chondrocytes apoptosis and the associated mechanism. DESIGN: Lysosomal acidification in Osteoarthritis (OA) and aged cartilage was determined by LysoSensor staining. Lysosomal function in chondrocytes was blocked by siRNA mediated depletion of Lysosomal Associated Membrane Protein 2 (LAMP2) or with lysosome inhibitors. Chondrocyte apoptosis was determined by LDH release, Caspase-3/7 activation, TUNEL and PI uptake assays. Loss of mitochondrial membrane potential (MMP/ΔΨM) and mitochondrial superoxide level was determined by JC-1 and MitoSOX staining, respectively. Colocalization of mitochondria with BCL2 associated X (BAX) and Cytochrome c was determined by immunostaining. Destabilization of medial meniscus (DMM) was performed to induce OA in mice. RESULTS: Lysosomal acidification was found to be significantly decreased in aged mouse and human and mouse OA cartilage which also showed increased chondrocyte apoptosis. Inhibition of lysosomal function resulted in increased oxidative stress, accumulation of dysfunctional mitochondria and apoptosis in chondrocytes in monolayer and in cartilage explant cultures. Depletion of LAMP2 expression or treatment of chondrocytes with lysosomal function inhibitors increased the expression and mitochondrial translocation of BAX leading to Cytochrome c release. Lysosomal dysfunction-induced apoptosis in chondrocytes was not blocked by antioxidants MitoTempo or Diphenyleneiodonium (DPI) but was abrogated by inhibiting BAX. CONCLUSION: Lysosomal dysfunction induce apoptosis in chondrocytes through BAX-mediated mitochondrial damage and release of Cytochrome c. Our data points to lysosomal function restoration and/or BAX inhibition in chondrocytes as a therapeutic approach for OA.

tRNA-derived fragments (tRFs) regulate post-transcriptional gene expression via AGO-dependent mechanism in IL-1ß stimulated chondrocytes.

OBJECTIVES: Recent studies have shown that tRNA-derived RNA fragments (tRFs) are novel regulators of post-transcriptional gene expression. However, the expression profiles and their role in post-transcriptional gene regulation in chondrocytes is unknown. Here, we determined tRFs expression profile and explored tRF-3003a role in post-transcriptional gene regulation in IL-1ß stimulated chondrocytes. METHODS: We used qPCR arrays to determine tRNAs and tRFs expression in age- and sex-matched primary human OA chondrocytes and TC28/I2 cells stimulated with IL-1ß. Chondrocytes were transfected with tRNA-CysGCA overexpression plasmid or tRF-3003a mimic and 3'UTR luciferase reporter plasmids of mRNAs harboring predicted tRF target "seed sequence". The AGO-RNA-induced silencing complex (AGO-RISC)-dependent repressive activity of tRF-3003a was determined by siRNA-mediated knockdown of AGO2. RESULTS: IL-1ß increased the expression levels of specific tRNAs and of tRF-3003a, a type 3 tRF produced by the cleavage of tRNA-CysGCA. tRF-3003a "seed sequence" was identified in the 3'UTR of JAK3 mRNA and tRNA-CysGCA overexpression or transfection of a tRF-3003a mimic in chondrocytes downregulated JAK3 expression and significantly reduced the activity of the 3'UTR reporter. RIP assay showed enrichment of tRF-3003a into AGO2/RISC in IL-1ß treated chondrocytes. The suppressive effect of tRF-3003a on JAK3 3'UTR reporter was abrogated with siRNA-mediated depletion of AGO2. CONCLUSIONS: We demonstrate that under pathological conditions chondrocytes display perturbations in the expression profile of specific tRNAs and tRFs. Furthermore, a specific tRF namely tRF-3003a can post-transcriptionally regulate JAK3 expression via AGO/RISC formation in chondrocytes. Identification of this novel mechanism may be of value in the design of precision therapies for OA.

Parkin clearance of dysfunctional mitochondria regulates ROS levels and increases survival of human chondrocytes.

OBJECTIVE: Mitochondrial dysfunction, oxidative stress and chondrocyte death are important contributors to the development and pathogenesis of osteoarthritis (OA). In this study, we determined the expression and role of Parkin in the clearance of damaged/dysfunctional mitochondria, regulation of reactive oxygen species (ROS) levels and chondrocyte survival under pathological conditions. METHODS: Human chondrocytes were from the unaffected area of knee OA cartilage (n = 12) and were stimulated with IL-1ß to mimic pathological conditions. Mitochondrial membrane depolarization and ROS levels were determined using specific dyes and flow cytometry. Autophagy was determined by Western blotting for ATG5, Beclin1, immunofluorescence staining and confocal microscopy. Gene expression was determined by RT-qPCR. siRNA, wild-type and mutant Parkin plasmids were transfected using Amaxa system. Apoptosis was determined by PI staining of chondrocytes and TUNEL assay. RESULTS: IL-1ß-stimulated OA chondrocytes showed high levels of ROS generation, mitochondrial membrane damage, accumulation of damaged mitochondria and higher incidence of apoptosis. IL-1ß stimulation of chondrocytes with depleted Parkin expression resulted in sustained high levels of ROS, accumulation of damaged/dysfunctional mitochondria and enhanced apoptosis. Parkin translocation to depolarized/damaged mitochondria and recruitment of p62/SQSTM1 was required for the elimination of damaged/dysfunctional mitochondria in IL-1ß-stimulated OA chondrocytes. Importantly we demonstrate that Parkin elimination of depolarized/damaged mitochondria required the Parkin ubiquitin ligase activity and resulted in reduced ROS levels and inhibition of apoptosis in OA chondrocytes under pathological conditions. CONCLUSIONS: Our data demonstrates that Parkin functions to eliminate depolarized/damaged mitochondria in chondrocytes which is necessary for mitochondrial quality control, regulation of ROS levels and chondrocyte survival under pathological conditions.

Spinigerin induces apoptotic like cell death in a caspase independent manner in Leishmania donovani.

Antimicrobial peptides (AMPs) are multifunctional components of the innate immune system. Chemotherapeutic agents used for treatment of visceral leishmaniasis (VL) are now threatened due to the emergence of acquired drug resistance and toxicity. AMPs are attractive alternative to conventional pharmaceuticals. In this study, first time we explored the antileishmanial activity of spinigerin originally derived from Pseudacanthotermes spiniger. Leishmania donovani promastigotes present apoptosis-like cell death upon exposure to spinigerin (IC50, 150 µM). The infection rate was reduced by 20% upon exposure to 150 µM spinigerin but no cytotoxicity on host macrophages was observed. Elevation of intracellular ROS level and down-regulation of two ROS detoxifying enzymes, ascorbate peroxidase (APx) and trypanothione reductase (TR) suggested essential role of ROS machinery during spinigerin mediated cell death. About 97% cell population was found to be Annexin-V positive; 44% cells being highly Annexin-V positive. Moreover, we observed morphological changes like cell rounding, nuclear condensation, oligonucleosomal DNA degradation and TUNEL positive cells without loss of membrane integrity upon spinigerin exposure, suggests apoptosis-like death. Interestingly, collapse in mitochondrial membrane potential and increased level of intracellular ROS and calcium were not associated with caspase like activity. Computational analysis suggests spiningerin interacts with trypanothione reductase and thus probably interferes its function to detoxify the toxic ROS level. Therefore, spinigerin induces apoptosis-like cell death in L. donovani in a caspase-independent manner. The study elucidates the antileishmanial property of spinigerin that may be considered for future chemotherapeutic option alone or adjunct with other drug regimens for improved treatment of visceral leishmaniasis.

Induction of phenotypic diversity in mutagenized population of lentil (Lens culinaris Medik) by using heavy metal.

Pulse breeding has been performed in the past by utilizing the genetic variability using conventional method. At the present time, these techniques are insufficient for producing new cultivars to fulfill globally increased food demand. In this situation, induced mutagenesis have been appeared as a new technique which are largely utilized for evolving improved mutants with good quality of agronomic traits and for determining desired genes that control agronomical traits. In the present investigation lentil seeds were mutagenized with different doses (5, 10, 15, 20 and 25 ppm) of lead and cadmium nitrate. M2 generation was raise from collected seeds of M1 generation. Distinct morphological mutants were selected with different traits such plant height, growth habit, leaf morphology, flower character, pigmentation and pod size. Different meiotic aberration such as stickiness, precocious separation of chromosome, unequal division, disturbed polarity with laggards, cytomixis, disorientation, unpolarized chromosome, sticky metaphase, multinucleate condition with micronuclei were also observed in this experiment. Some mutants may be utililised directly in selection or some of these are beneficial in breeding programme. Beneficial mutants were determined at lower concentrations both heavy metals with highest mutation frequency in cadmium than lead nitrate.

Genotoxic effects of heavy metal cadmium on growth, biochemical, cyto-physiological parameters and detection of DNA polymorphism by RAPD in Capsicum annuum L. - An important spice crop of India.

The present study was designed to investigate the effects of cadmium (Cd) on biochemical, physiological and cytological parameters of Capsicum annuum L. treated with five different concentrations (20, 40, 60, 80 and 100 ppm) of the metal. Shoot-root length, pigment and protein content showed a continuous decrease with increasing Cd concentrations and the maximal decline was observed at the higher concentration. Proline content was found to be increased upto 60 ppm while at higher concentrations it gradually decreased. MDA content and chromosomal aberrations increased as the concentration increased. Additionally Random amplified polymorphic DNA (RAPD) technique was used for the detection of genotoxicity induced by Cd. A total of 184 bands (62 polymorphic and 122 monomorphic) were generated in 5 different concentrations with 10 primers where primer OPA-02 generated the highest percentage of polymorphism (52.63%). Dendrogram showed that control, R1 and R2 showed similar cluster and R4 and R5 grouped with R3 into one cluster, which showed that plants from higher doses showed much difference than the plants selected at mild doses which resemble control at the DNA level. This investigation showed that RAPD marker is a useful tool for evaluation of genetic diversity and relationship among different metal concentrations.

Synergistic Cytotoxic Stress and DNA Damage in Clover (Trifolium repens) Exposed to Heavy Metal Soil from Automobile Refining Shops in Kashmir-Himalaya.

Coexposure to heavy metals occurs in many occupational settings, such as automobile refining shops, pigment, and batteries production. Heavy metals around automobile refining shops were tested for their ability to induce synergistic cytogenetic effects in Trifolium repens L. by using the chromosomal aberrasions (CAs), micronucleus (MN) and comet assay. A significant increase in micronucleus (MN), chromosomal abrations (CAs), percentage of nuclei with comet tails (NCTs), the relative comet tail length (CTL), comet tail DNA (CT, DNA), and tail moment (TM) were observed with increased concentration of three heavy metals, like Cd, Pb, Hg. The present result indicate that exposure of T. repens to soils contaminated by heavy metals around automobile refining shops shows clastogenicity, cytotoxicity, and DNA damage at higher concentrations.