SIRT6 and Premature Aging of Hutchinson-Gilford Progeria Syndrome Fibroblasts.

The genetic disease Hutchinson-Gilford Progeria Syndrome (HGPS) arises from a de novo single nucleotide mutation (1824CàT) in the LMNA gene. As a result, the mutated lamin A protein (progerin) remains farnesylated and permanently attached to the nuclear membrane. Progerin accumulates and deforms the nuclear membrane leading to an array of cellular abnormalities driving the cells to enter a state of permanent cell-cycle arrest early on in replicative age i.e. premature cellular senescence. Cellular senescence has been extensively studied as one of the contributing factors to aging in HGPS patients and other age-related diseases. There has also been evidence to show that aging is accompanied by epigenetic changes and that epigenetic manipulation can incite progeroid syndromes in mice. It has been found in this study that HGPS fibroblasts express distinctly lower levels of SIRT6, a member of the sirtuin family of NAD-dependent protein deacetylases/ADP-ribosyltransferases, than normal fibroblasts. Findings from this study demonstrate that overexpression of SIRT6 prevents a decrease in replicative capacity and the onset of premature senescence in HGPS fibroblasts. Thus, SIRT6 may have promising therapeutic implications for improving HGPS age-related pathologies

PPARγ deficiency results in severe, accelerated osteoarthritis associated with aberrant mTOR signalling in the articular cartilage

Objectives: We have previously shown that peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor, is essential for the normal growth and development of cartilage. In the present study, we created inducible cartilage-specific PPARγ knockout (KO) mice and subjected these mice to the destabilisation of medial meniscus (DMM) model of osteoarthritis (OA) to elucidate the specific in vivo role of PPARγ in OA pathophysiology. We further investigated the downstream PPARγ signalling pathway responsible for maintaining cartilage homeostasis. Methods: Inducible cartilage-specific PPARγ KO mice were generated and subjected to DMM model of OA. We also created inducible cartilage-specific PPARγ/mammalian target for rapamycin (mTOR) double KO mice to dissect the PPARγ signalling pathway in OA. Results: Compared with control mice, PPARγ KO mice exhibit accelerated OA phenotype with increased cartilage degradation, chondrocyte apoptosis, and the overproduction of OA inflammatory/catabolic factors associated with the increased expression of mTOR and the suppression of key autophagy markers. In vitro rescue experiments using PPARγ expression vector reduced mTOR expression, increased expression of autophagy markers and reduced the expression of OA inflammatory/catabolic factors, thus reversing the phenotype of PPARγ KO mice chondrocytes. To dissect the in vivo role of mTOR pathway in PPARγ signalling, we created and subjected PPARγ-mTOR double KO mice to the OA model to see if the genetic deletion of mTOR in PPARγ KO mice (double KO) can rescue the accelerated OA phenotype observed in PPARγ KO mice. Indeed, PPARγ-mTOR double KO mice exhibit significant protection/reversal from OA phenotype. Significance PPARγ maintains articular cartilage homeostasis, in part, by regulating mTOR pathway

MicroRNA-34a-5p Promotes Joint Destruction During Obesity and Osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease and the most common cause of disability among older individuals. We previously found that levels of microRNA-34a-5p (miR-34a-5p) in synovial fluid increase during late-stage (grade III/IV) compared to grade I/II radiographic knee OA; however, the role of miR-34a-5p in OA pathophysiology and its potential as a therapeutic target is largely unknown. In the current study, I found that miR-34a-5p expression was increased in the plasma, knee articular cartilage and synovial tissue of total knee replacement (TKR) patients compared to healthy controls and early OA synovial tissue. Similarly, miR-34a-5p expression was increased in knee joint tissues of a surgically-induced (destabilization of medial meniscus (DMM)) mouse model of OA. Since obesity is a significant risk factor for OA development, I first showed that plasma miR-34a-5p expression was further elevated in obese versus non obese OA patients. In addition, miR-34a-5p expression was highly elevated in plasma and knee joints of obese mice subjected to high fat diet. My in vitro studies revealed that miR-34a-5p mimic promoted critical mediators involved in catabolic processes in human chondrocytes and increased expression of synovitis-associated markers in human fibroblast-like synoviocytes (FLS). Conversely, miR-34a-5p antisense oligonucleotide (ASO) treatment promoted anabolic effects in chondrocytes and reduced the expression of pro-fibrotic and pro-inflammatory markers in FLS. In conjunction with my in vitro findings, intra-articular injection of miR-34a-5p mimic in mice induced OA pathological changes such as cartilage degeneration and synovitis. Notably, my preclinical studies conclusively demonstrated the therapeutic potential of intra-articular injections of miR-34a-5p ASO, which imparted cartilage-protective effects in both normal weight and high-fat diet-fed mice subjected to OA surgery. To investigate the regulatory mechanisms of miR-34a-5p in articular cartilage, chondrocytes obtained from miR-34a knock out (KO) mice or wild-types (WT) were subjected to RNA Sequencing and putative signaling pathways regulated by miR-34a-5p were determined. This is the first study to propose a link between obesity and OA via dysregulated miR-34a-5p expression and provides first preclinical evidence for OA therapeutic intervention using a miR-34a-5p ASO.Ph.D.2020-11-13 00:00:0