Objective: Aging is associated with reduced central nervous system endocannabinoid tone. Here we ‎sought to decipher the involvement of hypothalamic cannabinoid receptor type-1 (Cnr1) in ‎driving peripheral tissue aging, with a particular focus on bone and joint structural changes.

Methods: To this end, we generated mice with hypothalamus-specific ablation of Cnr1 (i.e., CB1^hypoKO), or with hypothalamus-specific rescue of the receptor (CB1^STOPhypoRS) using stereotaxic viral injections into the mediobasal hypothalamus at 2-3-‎months of age in Cnr1^fl/fl or CB1^STOP mice. Animals were aged to 18 or 19 months and assessed for body weight, ‎temperature, frailty and circulating hormones. After sacrifice, we examined structural and histological features of hypothalamic tissue, skin, ‎testis, joint, and bone as well as circulating hormone levels.

Results: CB1^hypoKO exhibited reduced frailty index vs WT at 17 months of age, with unchanged body weight, temperature and survival. Interestingly, CB1^hypoKO mice displayed a reduction in the lateral meniscal ‎mineral volume of the tibiofemoral joint, which was associated with less blood vessels and articular cartilage damage. Immunofluorescence analysis revealed that CB1^hypoKO mice displayed enriched tyrosine hydroxylase (TH) intensity surrounding blood vessels, yet meniscal tissue showed reduced TH positive cells and ATF4 nuclear co-appearence in CB1^hypoKO mice vs WT. Finally, CB1^hypoKO mice displayed signficantly lower circulating levels of corticosterone.

Conclusions: These results suggest that a lack of hypothalamic CB1 tone reduced circulating levesl of corticosterone, while increasing local meniscal sympathetic tone, which is associated with impaired ATF4 nuclear localization and meniscal mineralization. These events subsequently hinder OA development with age.

Osteoarthritis (OA) is characterized by progressive, irreversible erosion of articular cartilage accompanied by severe pain and immobility. This study aimed to assess the effect and mechanism of action of HU308, a selective cannabinoid receptor type 2 (CB2) agonist, in preventing OA-related joint damage. To test the assumption that HU308 could prevent OA-related joint damage, Cnr2 null mice and wild type (WT) mice were aged to reach 20 months and analyzed for joint structural features. OA was induced in WT mice via a post-traumatic procedure or aging, followed by HU308 local (intra-articular) or systemic (intraperitoneal) administration, respectively. Additional analyses of time and dose courses for HU308 were carried out in human primary chondrocytes, analyzed by RNA sequencing, RT-PCR, chromatin immunoprecipitation, and immunoblotting. Our results showed that Cnr2 null mice exhibited enhanced age-related OA severity and synovitis compared to age-matched WT mice. Systemic administration of HU308 to 16-month-old mice improved pain sensitivity and maintained joint integrity, which was consistent with the intra-articular administration of HU308 in post-traumatic OA mice. When assessing human chondrocytes treated with HU308, we uncovered a dose- and time-related increase in ACAN and COL2A1 expression, which was preceded by increased SOX9 expression due to pCREB transcriptional activity. Finally, transcriptomic analysis of patient-derived human chondrocytes identified patient subpopulations exhibiting HU308-responsive trends as judged by enhanced SOX9 expression, accompanied by enriched gene networks related to carbohydrate metabolism. Collectively, the results showed that HU308 reduced trauma and age-induced OA via CB2-pCREB dependent activation of SOX9, contributing to augmented gene networks related to carbohydrate metabolism. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

In contrast to normal regenerating tissue, resistance to Fas-and FasL-positive T cell-induced apoptosis were detected in myofibroblasts from fibrotic-lungs of humans and mice following bleomycin (BLM) exposure. In this study we show, decreased FLIP expression in lung-tissues with resolution of BLM-induced fibrosis and in isolated-lung fibroblasts, with decreased resistance to apoptosis. Using a FLIP-expression vector or a shFLIP-RNA, we further confirmed the critical need for FLIP to regain/lose susceptibility of fibrotic-lung myofibroblast to Fas-induced apoptosis. Our study further show that FLIP is regulated by SIRT1 (Sirtuin 1) deacetylase. Chimeric mice, with SIRT1-deficiency in deacetylase domain (H355Y-Sirt1y/y), specifically in mesenchymal cells, were not only protected from BLM-induced lung fibrosis but, as assessed following Ku70 immunoprecipitation, had also decreased Ku70-deacetylation, decreasedKu70/FLIP complex, and decreased FLIP levels in their lung myofibroblasts. In addition, myofibroblasts isolated from lungs of BLM-treated miR34a-knockout mice, exposed to a miR34a mimic, which we found here to downregulate SIRT1 in the luciferase assay, had a decreased Ku70-deacetylation indicating decrease in SIRT1 activity. Thus, SIRT1 may mediate, miR34a-regulated, persistent FLIP levels by deacetylation of Ku70 in lung myofibroblasts, promoting resistance to cell-death and lung fibrosis. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.