Inhibition of protein kinase-D promotes cartilage repair at injured growth plate in rats

Small Molecule Inhibitors of Protein Kinase D: Early Development, Current Approaches, and Future Directions

Now entering its fourth decade, research on the biological function, small molecule inhibition, and disease relevance of the three known isoforms of protein kinase D, PKD1, PKD2, and PKD3, has entered a mature development stage. This mini-perspective focuses on the medicinal chemistry that provided a structurally diverse set of mainly active site inhibitors, which, for a brief time period, moved through preclinical development stages but have yet to be tested in clinical trials. In particular, between 2006 and 2012, a rapid expansion of synthetic efforts led to several moderately to highly PKD-selective chemotypes but did not yet achieve PKD subtype selectivity or resolve general toxicity and pharmacokinetic challenges. In addition to cancer, other unresolved medical needs in cardiovascular, inflammatory, and metabolic diseases would, however, benefit from a renewed focus on potent and selective PKD modulators.

Tissue engineering in growth plate cartilage regeneration: Mechanisms to therapeutic strategies

The repair of growth plate injuries is a highly complex process that involves precise spatiotemporal regulation of multiple cell types. While significant progress has been made in understanding the pathological mechanisms underlying growth plate injuries, effectively regulating this process to regenerate the injured growth plate cartilage remains a challenge. Tissue engineering technology has emerged as a promising therapeutic approach for achieving tissue regeneration through the use of functional biological materials, seed cells and biological factors, and it is now widely applied to the regeneration of bone and cartilage. However, due to the unique structure and function of growth plate cartilage, distinct strategies are required for effective regeneration. Thus, this review provides an overview of current research on the application of tissue engineering to promote growth plate regeneration. It aims to elucidates the underlying mechanisms by which tissue engineering promotes growth plate regeneration and to provide novel insights and therapeutic strategies for future research on the regeneration of growth plate.

Polyelectrolyte Complex Hydrogels with Controlled Mechanics Affect Mesenchymal Stem Cell Differentiation Relevant to Growth Plate Injuries

The growth plate is a complex cartilage structure in long bones that mediates growth in children. When injured, the formation of a "bony bar" can occur which impedes normal growth and can cause angular deformities or growth arrest. Current treatments for growth plate injuries are limited and result in poor patient outcomes, necessitating research toward novel treatments that can prevent bony bar formation and stimulate cartilage regeneration. This study investigates alginate-chitosan polyelectrolyte complex (PEC) hydrogels as an injectable biomaterial system to prevent bony bar formation. Biomaterial properties including stiffness and degradation are quantified, and the effect that material properties have on mesenchymal stem cell (MSC) fate is quantified in vitro. Specifically, this study aims to elucidate the effectiveness of biomaterial-based control over the differentiation behavior of MSCs toward osteogenic or chondrogenic lineages using biochemical metabolite assays and quantitative real time PCR. Further, the PEC hydrogels are employed in a rat growth plate injury model to determine their effectiveness in preventing bony bar formation in vivo. Results indicate that hydrogel composition and material properties affect the differentiation tendency of MSCs in vitro, and the PEC hydrogels show promise as an injectable biomaterial for growth plate injuries.

Nanosome-Mediated Delivery Of Protein Kinase D Inhibitor Protects Chondrocytes From Interleukin-1β-Induced Stress And Apoptotic Death

Background

Inflammatory stress caused by protein kinase D (PKD) plays a critical role in damaging chondrocytes and extracellular matrix (ECM) during osteoarthritis (OA). The PKD inhibitor (PKDi) (CRT0066101) has been used to overcome inflammation in different cell types. However, the efficacy of a therapeutic drug can be limited due to off-target distribution, slow cellular internalization, and limited lysosomal escape. In order to overcome this issue, we developed nanosomes carrying CRT0066101 (PKDi-Nano) and tested their efficacy in vitro in chondrocytes.

Methods

Chondrocytes were subjected to IL-1β-induced inflammatory stress treated with either PKDi or PKDi-Nano. Effects of treatment were measured in terms of cytotoxicity, cellular morphology, viability, apoptosis, phosphorylation of protein kinase B (Akt), and anabolic/catabolic gene expression analyses related to cartilage tissue.

Results and Discussion

The effects of PKDi-Nano treatment were more pronounced as compared to PKDi treatment. Cytotoxicity and apoptosis were significantly reduced following PKDi-Nano treatment (P < 0.001). Cellular morphology was also restored to normal size and shape. The viability of chondrocytes was significantly enhanced in PKDi-Nano-treated cells (P < 0.001). The data indicated that PKDi-Nano acted independently of the Akt pathway. Gene expression analyses revealed significant increases in the expression levels of anabolic genes with concomitant decreases in the level of catabolic genes. Our results indicate that PKDi-Nano attenuated the effects of IL-1β via the nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) pathway.

Conclusion

Taken together, these results suggest that PKDi-Nano can be used as a successful strategy to reduce IL1β-induced inflammatory stress in chondrocytes.

Osteoblast derived-neurotrophin‑3 induces cartilage removal proteases and osteoclast-mediated function at injured growth plate in rats

Faulty bony repair causes dysrepair of injured growth plate cartilage and bone growth defects in children; however, the underlying mechanisms are unclear. Recently, we observed the prominent induction of neurotrophin‑3 (NT-3) and its important roles as an osteogenic and angiogenic factor promoting the bony repair. The current study investigated its roles in regulating injury site remodelling. In a rat tibial growth plate drill-hole injury repair model, NT-3 was expressed prominently in osteoblasts at the injury site. Recombinant NT-3 (rhNT-3) systemic treatment enhanced, but NT-3 immunoneutralization attenuated, expression of cartilage-removal proteases (MMP-9 and MMP-13), presence of bone-resorbing osteoclasts and expression of osteoclast protease cathepsin K, and remodelling at the injury site. NT-3 was also highly induced in cultured mineralizing rat bone marrow stromal cells, and the conditioned medium augmented osteoclast formation and resorptive activity, an ability that was blocked by presence of anti-NT-3 antibody. Moreover, NT-3 and receptor TrkC were induced during osteoclastogenesis, and rhNT-3 treatment activated TrkC downstream kinase Erk1/2 in differentiating osteoclasts although rhNT-3 alone did not affect activation of osteoclastogenic transcription factors NF-κB or NFAT in RAW_264.7 osteoclast precursor cells. Furthermore, rhNT-3 treatment increased, but NT-3 neutralization reduced, expression of osteoclastogenic cytokines (RANKL, TNF-α, and IL-1) in mineralizing osteoblasts and in growth plate injury site, and rhNT-3 augmented the induction of these cytokines caused by RANKL treatment in RAW_264.7 cells. Thus, injury site osteoblast-derived NT-3 is important in promoting growth plate injury site remodelling, as it induces cartilage proteases for cartilage removal and augments osteoclastogenesis and resorption both directly (involving activing Erk1/2 and substantiating RANKL-induced increased expression of osteoclastogenic signals in differentiating osteoclasts) and indirectly (inducing osteoclastogenic signals in osteoblasts).

A Conditional Knockout Mouse Model Reveals a Critical Role of PKD1 in Osteoblast Differentiation and Bone Development

The protein kinase D family of serine/threonine kinases, particularly PKD1, has been implicated in the regulation of a complex array of fundamental biological processes. However, its function and mechanism underlying PKD1-mediated the bone development and osteoblast differentiation are not fully understood. Here we demonstrate that loss of PKD1 function led to impaired bone development and osteoblast differentiation through STAT3 and p38 MAPK signaling using in vitro and in vivo bone-specific conditional PKD1-knockout (PKD1-KO) mice models. These mice developed markedly craniofacial dysplasia, scapula dysplasia, long bone length shortage and body weight decrease compared with wild-type littermates. Moreover, deletion of PKD1 in vivo reduced trabecular development and activity of osteoblast development, confirmed by Micro-CT and histological staining as well as expression of osteoblastic marker (OPN, Runx2 and OSX). Mechanistically, loss of PKD1 mediated the downregulation of osteoblast markers and impaired osteoblast differentiation through STAT3 and p38 MAPK signaling pathways. Taken together, these results demonstrated that PKD1 contributes to the osteoblast differentiation and bone development via elevation of osteoblast markers through activation of STAT3 and p38 MAPK signaling pathways.

Antithetical regulation of α-myosin heavy chain between fetal and adult heart failure though shuttling of HDAC5 regulating YY-1 function

Molecular switches of myosin isoforms are known to occur in various conditions. Here, we demonstrated the result from fetal heart failure and its potential mechanisms. Fetal and adult heart failure rat models were induced by injections of isoproterenol as previously described, and Go6976 was given to heart failing fetuses. Real-time PCR and Western blot were adopted to measure the expressions of α-MHC, β-MHC and YY-1. Co-immunoprecipitation was performed to analysis whether YY-1 interacts with HDAC5. Besides, histological immunofluorescence assessment was carried out to identify the location of HDAC5. α-MHC was recorded elevated in fetal heart failure which was decreased in adult heart failure. Besides, YY-1 was observed elevated both in fetal and adult failing hearts, but YY-1 could co-immunoprecipitation with HDAC5 only in adult hearts. Nuclear localization of HDAC5 was identified in adult cardiomyocytes, while cytoplasmic localization was identified in fetuses. After Go6976 supplied, HDAC5 shuttled into nucleuses interacted with YY-1. The myosin molecular switches were reversed with worsening cardiac functions and higher mortalities. Regulation of MHC in fetal heart failure was different from adult which provided a better compensation with increased α-MHC. This kind of transition was involved with shuttling of HDAC5 regulating YY-1 function.

Recent research on the growth plate: Mechanisms for growth plate injury repair and potential cell-based therapies for regeneration

Injuries to the growth plate cartilage often lead to bony repair, resulting in bone growth defects such as limb length discrepancy and angulation deformity in children. Currently utilised corrective surgeries are highly invasive and limited in their effectiveness, and there are no known biological therapies to induce cartilage regeneration and prevent the undesirable bony repair. In the last 2 decades, studies have investigated the cellular and molecular events that lead to bony repair at the injured growth plate including the identification of the four phases of injury repair responses (inflammatory, fibrogenic, osteogenic and remodelling), the important role of inflammatory cytokine tumour necrosis factor alpha in regulating downstream repair responses, the role of chemotactic and mitogenic platelet-derived growth factor in the fibrogenic response, the involvement and roles of bone morphogenic protein and Wnt/B-catenin signalling pathways, as well as vascular endothelial growth factor-based angiogenesis during the osteogenic response. These new findings could potentially lead to identification of new targets for developing a future biological therapy. In addition, recent advances in cartilage tissue engineering highlight the promising potential for utilising multipotent mesenchymal stem cells (MSCs) for inducing regeneration of injured growth plate cartilage. This review aims to summarise current understanding of the mechanisms for growth plate injury repair and discuss some progress, potential and challenges of MSC-based therapies to induce growth plate cartilage regeneration in combination with chemotactic and chondrogenic growth factors and supporting scaffolds.

The potential role of VEGF-induced vascularisation in the bony repair of injured growth plate cartilage

Growth plate injuries often result in undesirable bony repair causing bone growth defects, for which the underlying mechanisms are unclear. Whilst the key importance of pro-angiogenic vascular endothelial growth factor (VEGF) is well-known in bone development and fracture repair, its role during growth plate bony repair remains unexplored. Using a rat tibial growth plate injury repair model with anti-VEGF antibody, Bevacizumab, as a single i.p. injection (2.5 mg/kg) after injury, this study examined the roles of VEGF-driven angiogenesis during growth plate bony repair. Histology analyses observed isolectin-B4-positive endothelial cells and blood vessel-like structures within the injury site on days 6 and 14, with anti-VEGF treatment significantly decreasing blood-vessel-like structures within the injury site (P<0.05). Compared with untreated controls, anti-VEGF treatment resulted in an increase in undifferentiated mesenchymal repair tissue, but decreased bony tissue at the injury site at day 14 (P<0.01). Consistently, microcomputed tomography analysis of the injury site showed significantly decreased bony repair tissue after treatment (P<0.01). RT-PCR analyses revealed a significant decrease in osteocalcin (P<0.01) and a decreasing trend in Runx2 expression at the injury site following treatment. Furthermore, growth plate injury-induced reduced tibial lengthening was more pronounced in anti-VEGF-treated injured rats on day 60, consistent with the observation of a significantly increased height of the hypertrophic zone adjacent to the growth plate injury site (P<0.05). These results indicate that VEGF is important for angiogenesis and formation of bony repair tissue at the growth plate injury site as well as for endochondral bone lengthening function of the uninjured growth plate.