Adaptation to ER Stress Is Mediated by Differential Stabilities of Pro-Survival and Pro-Apoptotic mRNAs and Proteins

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) activates a signaling cascade known as the unfolded protein response (UPR). Although activation of the UPR is well described, there is little sense of how the response, which initiates both apoptotic and adaptive pathways, can selectively allow for adaptation. Here we describe the reconstitution of an adaptive ER stress response in a cell culture system. Monitoring the activation and maintenance of representative UPR gene expression pathways that facilitate either adaptation or apoptosis, we demonstrate that mild ER stress activates all UPR sensors. However, survival is favored during mild stress as a consequence of the intrinsic instabilities of mRNAs and proteins that promote apoptosis compared to those that facilitate protein folding and adaptation. As a consequence, the expression of apoptotic proteins is short-lived as cells adapt to stress. We provide evidence that the selective persistence of ER chaperone expression is also applicable to at least one instance of genetic ER stress. This work provides new insight into how a stress response pathway can be structured to allow cells to avert death as they adapt. It underscores the contribution of posttranscriptional and posttranslational mechanisms in influencing this outcome

Closed second metatarsal head intra-articular fractures: Case series and review of literature

Intra-articular fractures can produce degenerative changes causing continued pain and disability, therefore optimal surgical care might be indicated. Metatarsal (MT) intra-articular are no exception. While prior literature described mainly intra-articular fractures of the first MT and lateral toes, there is scarce literature addressing fractures of the second MT head, which is the longest and most robust MT bone. In this case series, we report three cases of second MT head fracture-dislocation and their clinical outcomes. We also review the literature addressing this pathology

Partial Calcanectomy for Heel Ulcers Revisited – a Possible Solution to a Difficult Problem

Category: Diabetes Introduction/Purpose: Diabetic heel ulcers are a major problem, often leading to amputations. Partial or total calcanectomy has been described as a possible salvage procedure, by allowing soft tissue coverage after debridement of necrotic and infected tissue, and possibly allowing walking. We report on our experience with this technique which is not commonly used Methods: Fourteen patients, who presented with diabetic heel ulcers between 2010-15, and who were BKA candidates, underwent debridement and partial calcanectomy. Average age was 67.8 ±12.7 years, M:F ratio was 6:1 Extent of procedures, need for additional procedures and complications were noted. Outcome assessment included wound closure and walking status. No patients were lost to follow up. Results: Nine patients underwent partial calcanectomy as the initial procedure while others underwent prior debridement. Calcanectomies were subtotal (1), wedge (5) or partial (8). Primary closure was mostly achieved (11), the remainder requiring local skin graft (2) or myocutaneous flap (1). Ten patients underwent re-vascularization prior to calcanectomy, either angiographic (8) or bypass (2). Most calcanectomies (9/14) healed successfully, while five subsequently required amputations. Most failures were noticed within 24 days, with similar prevalence in wedge and partial calcanectomies. One patient had wound complications requiring BKA. At one year, the nine patients had full wound closure and could bear weight. Five patients regained full ambulatory status wearing specially modified shoes with custom fillers. Conclusion: Partial calcanectomy is a little-known procedure, that is a viable alternative to BKA. We present our positive experience with this procedure, which in a majority of cases not only prevented BKA, but also allowed weight bearing. Poor vascular supply is not necessarily a contraindication, as re-vascularization prior to calcanectomy is a viable option

Regeneration of injured articular cartilage using the recombinant human amelogenin protein

Aims: Cartilage injuries rarely heal spontaneously and often require surgical intervention, leading to the formation of biomechanically inferior fibrous tissue. This study aimed to evaluate the possible effect of amelogenin on the healing process of a large osteochondral injury (OCI) in a rat model. Methods: A reproducible large OCI was created in the right leg femoral trochlea of 93 rats. The OCIs were treated with 0.1, 0.5, 1.0, 2.5, or 5.0 μg/μl recombinant human amelogenin protein (rHAM+) dissolved in propylene glycol alginate (PGA) carrier, or with PGA carrier alone. The degree of healing was evaluated 12 weeks after treatment by morphometric analysis and histological evaluation. Cell recruitment to the site of injury as well as the origin of the migrating cells were assessed four days after treatment with 0.5 μg/μl rHAM+ using immunohistochemistry and immunofluorescence. Results: A total of 12 weeks after treatment, 0.5 μg/μl rHAM+ brought about significant repair of the subchondral bone and cartilage. Increased expression of proteoglycan and type II collagen and decreased expression of type I collagen were revealed at the surface of the defect, and an elevated level of type X collagen at the newly developed tide mark region. Conversely, the control group showed osteoarthritic alterations. Recruitment of cells expressing the mesenchymal stem cell (MSC) markers CD105 and STRO-1, from adjacent bone marrow toward the OCI, was noted four days after treatment. Conclusion: We found that 0.5 μg/μl rHAM+ induced in vivo healing of injured articular cartilage and subchondral bone in a rat model, preventing the destructive post-traumatic osteoarthritic changes seen in control OCIs, through paracrine recruitment of cells a few days after treatment. Cite this article: Bone Joint Res 2023;12(10):615–623

Serum NT/CT SIRT1 ratio reflects early osteoarthritis and chondrosenescence

Abstract Objective: Previous work has established that the deacetylase sirtuin-1 (SIRT1) is cleaved by cathepsin B in chondrocytes subjected to proinflammatory stress, yielding a stable but inactive N-terminal (NT) polypeptide (75SIRT1) and a C-terminal (CT) fragment. The present work examined if chondrocyte-derived NT-SIRT1 is detected in serum and may serve as an investigative and exploratory biomarker of osteoarthritis (OA). Methods: We developed a novel ELISA assay to measure the ratio of NT to CT of SIRT1 in the serum of human individuals and mice subjected to post-traumatic OA (PTOA) or age-dependent OA (ADOA). We additionally monitored NT/CT SIRT1 in mice subject to ADOA/PTOA followed by senolytic clearance. Human chondrosenescent and non-senescent chondrocytes were exposed to cytokines and analysed for apoptosis and NT/CT SIRT1 ratio in conditioned medium. Results: Wild-type mice with PTOA or ADOA of moderate severity exhibited increased serum NT/CT SIRT1 ratio. In contrast, this ratio remained low in cartilage-specific Sirt1 knockout mice despite similar or increased PTOA and ADOA severity. Local clearance of senescent chondrocytes from old mice with post-traumatic injury resulted in a lower NT/CT ratio and reduced OA severity. While primary chondrocytes exhibited NT/CT ratio increased in conditioned media after prolonged cytokine stimulation, this increase was not evident in cytokine-stimulated chondrosenescent cells. Finally, serum NT/CT ratio was elevated in humans with early-stage OA. Conclusions: Increased levels of serum NT/CT SIRT1 ratio correlated with moderate OA in both mice and humans, stemming at least in part from non-senescent chondrocyte apoptosis, possibly a result of prolonged inflammatory insult