Growth plate cartilage shows different strain patterns in response to static versus dynamic mechanical modulation

Association of IL‑6 and MMP‑3 gene polymorphisms with adolescent idiopathic scoliosis: A systematic review and meta‑analysis

The pathogenesis of adolescent idiopathic scoliosis (AIS) remains unclear. It has been found that interleukin-6 (IL-6) rs1800795 locus and matrix metalloproteinase-3 (MMP-3) rs3025058 locus gene polymorphisms may be associated with AIS susceptibility, which has been controversial and needs to be further confirmed by updated meta-analysis. The aim of the present study was to investigate the association of MMP-3 rs3025058 and IL-6 rs1800795 single nucleotide polymorphisms (SNPs) with susceptibility to AIS. All relevant articles that met the criteria were retrieved and included, and the publication dates were limited from January 2005 to December 2023. The allele frequencies and different genotype frequencies of IL-6 rs1800795 and MMP-3 rs3025058 loci in each study were extracted and statistically analyzed by ReviewManager 5.4 software, and the odds ratio (OR) and 95% confidence interval (95% CI) of different genetic models were calculated. The results of the meta-analysis showed that there was no significant association between the gene polymorphism of IL-6 rs1800795 locus and the pathogenesis of AIS. The allele 5A and genotype 5A5A of MMP-3 rs3025058 SNP were associated with AIS susceptibility (5A vs. 6A, OR=1.18; 95% CI, 1.04-1.33; 5A5A vs. 6A6A, OR=1.65; 95% CI, 1.23-2.21; and 5A5A vs. 5A6A + 6A6A, OR=1.54; 95% CI, 1.19-1.99). Results of subgroup analysis revealed that the allele 5A and genotype 5A5A of MMP-3 rs3025058 SNP were associated with AIS susceptibility in the Caucasian population, and the susceptibility of AIS was associated with the genotype 5A5A of MMP-3 rs3025058 SNP in an Asian population. There was no significant association between the gene polymorphism of IL-6 rs1800795 locus and the pathogenesis of AIS, while the allele 5A of MMP-3 rs3025058 locus was associated with the susceptibility to AIS, especially in the Caucasian population.

Effect of hip dysplasia on the development of the femoral head growth plate

Purpose

The purpose of this study was to observe whether developmental dysplasia of the hip (DDH) affects the development of the femoral head growth plate and to analyze the risk factors.

Methods

We selected female patients aged between 11 and 20 years with unilateral DDH and unclosed femoral head growth plate (s). The selected patients underwent anteroposterior radiography of the hip joint to compare the degree of development of the femoral head growth plate on both sides and to identify risk factors that affect the development of the growth plate in the femoral head.

Results

We included 48 female patients with unilateral DDH, with an average age of 14 years (range: 11.1-18.5 years) and an average BMI of 20.4 kg/m² (range: 15.5 kg/m²-27.9 kg/m²). Among them, 23 patients had earlier development of the femoral head growth plate on the affected side than on the healthy side, while the degree of development of the femoral head growth plate in 25 patients was the same as that on the contralateral side. When the Tönnis angle was greater than 29.5°C and/or the Reimers migration index was greater than 48.5%, there was a statistically significant difference in the acceleration of femoral head growth plate development.

Conclusion

An abnormal relative position of the acetabulum-femoral head caused by DDH can accelerate closure of the femoral head growth plate in immature female patients. The risk factors are a Tönnis angle greater than 29.5°C and/or Reimers migration index greater than 48.5%.

Growing Pains: The Need for Engineered Platforms to Study Growth Plate Biology

Growth plates, or physis, are highly specialized cartilage tissues responsible for longitudinal bone growth in children and adolescents. Chondrocytes that reside in growth plates are organized into three distinct zones essential for proper function. Modeling key features of growth plates may provide an avenue to develop advanced tissue engineering strategies and perspectives for cartilage and bone regenerative medicine applications and a platform to study processes linked to disease progression. In this review, a brief introduction of the growth plates and their role in skeletal development is first provided. Injuries and diseases of the growth plates as well as physiological and pathological mechanisms associated with remodeling and disease progression are discussed. Growth plate biology, namely, its architecture and extracellular matrix organization, resident cell types, and growth factor signaling are then focused. Next, opportunities and challenges for developing 3D biomaterial models to study aspects of growth plate biology and disease in vitro are discussed. Finally, opportunities for increasingly sophisticated in vitro biomaterial models of the growth plate to study spatiotemporal aspects of growth plate remodeling, to investigate multicellular signaling underlying growth plate biology, and to develop platforms that address key roadblocks to in vivo musculoskeletal tissue engineering applications are described.

Cyclic mechanical strain with high-tensile triggers autophagy in growth plate chondrocytes

Background

Mechanical loading has been widely considered to be essential for growth plate to maintain metabolism and development. Cyclic mechanical strain has been demonstrated to induce autophagy, whereas the relationship between cyclic tensile strain (CTS) and autophagy in growth plate chondrocytes (GPCs) is not clear. The objective of this study was to investigate whether CTS can regulate autophagy in GPCs in vitro and explore the potential mechanisms of this regulation.

Methods

The 2-week-old Sprague–Dawley rat GPCs were subjected to CTS of varying magnitude and duration at a frequency of 2.0 Hz. The mRNA levels of autophagy-related genes were measured by RT-qPCR. The autophagy in GPCs was verified by transmission electron microscopy (TME), immunofluorescence and Western blotting. The fluorescence-activated cell sorting (FACS) was employed to detect the percentage of apoptotic and necrotic cells.

Results

In GPCs, CTS significantly increased the mRNA and protein levels of autophagy-related genes, such as LC3, ULK1, ATG5 and BECN1 in a magnitude- and time-dependent manner. There was no significant difference in the proportion of apoptotic and necrotic cells between control group and CTS group. The autophagy inhibitors, 3-methyladenine (3MA) and chloroquine (CQ) reversed the CTS-induced autophagy via promoting the formation of autophagosomes. Cytochalasin D (cytoD), an inhibitor of G-actin polymerization into F-actin, could effectively block the CTS-induced autophagy in GPCs.

Conclusion

Cyclic mechanical strain with high-tensile triggers autophagy in GPCs, which can be suppressed by 3MA and CQ, and cytoskeletal F-actin microfilaments organization plays a key role in chondrocytes’ response to mechanical loading.

Properties of Cartilage-Subchondral Bone Junctions: A Narrative Review with Specific Focus on the Growth Plate

OBJECTIVE

The purpose of this narrative review is to summarize what is currently known about the structural, chemical, and mechanical properties of cartilage-bone interfaces, which provide tissue integrity across a bimaterial interface of 2 very different structural materials. Maintaining these mechanical interfaces is a key factor for normal bone growth and articular cartilage function and maintenance.

MATERIALS AND METHODS

A comprehensive search was conducted using Google Scholar and PubMed/Medline with a specific focus on the growth plate cartilage-subchondral bone interface. All original articles, reviews in journals, and book chapters were considered. Following a review of the overall structural and functional characteristics of the physis, the literature on histological studies of both articular and growth plate chondro-osseous junctions is briefly reviewed. Next the literature on biochemical properties of these interfaces is reviewed, specifically the literature on elemental analyses across the cartilage-subchondral bone junctions. The literature on biomechanical studies of these junctions at the articular and physeal interfaces is also reviewed and compared.

RESULTS

Unlike the interface between articular cartilage and bone, growth plate cartilage has 2 chondro-osseous junctions. The reserve zone of the mature growth plate is intimately connected to a plate of subchondral bone on the epiphyseal side. This interface resembles that between the subchondral bone and articular cartilage, although much less is known about its makeup and formation.

CONCLUSION

There is a notably paucity of information available on the structural and mechanical properties of reserve zone-subchondral epiphyseal bone interface. This review reveals that further studies are needed on the microstructural and mechanical properties of chondro-osseous junction with the reserve zone.

Part 2. Review and meta-analysis of studies on modulation of longitudinal bone growth and growth plate activity: A micro-scale perspective

Macro-scale changes in longitudinal bone growth resulting from mechanical loading were shown in Part 1 of this review to depend on load magnitude, anatomical location, and species. While no significant effect on longitudinal growth was observed by varying frequency and amplitude of cyclic loading, such variations, in addition to loading duration and species, were shown to affect the morphology, viability, and gene and protein expression within the growth plate. Intermittent compression regimens were shown to preserve or increase growth plate height while stimulating increased chondrocyte presence in the hypertrophic zone relative to persistent and static loading regimens. Gene and protein expressions related to matrix synthesis and degradation, as well as regulation of chondrocyte apoptosis were shown to exhibit magnitude-, frequency-, and duration-dependent responses to loading regimen. Chondrocyte viability was shown to be largely preserved within physiological bounds of magnitude, frequency, amplitude, and duration. Persistent static loading was shown to be associated with overall growth plate height in tension only, reducing it in compression, while affecting growth plate zone heights differently across species and encouraging mineralization relative to intermittent cyclic loading. Lateral loading of the growth plate, as well as microfluidic approaches are relatively understudied, and age, anatomical location, and species effects within these approaches are undefined. Understanding the micro-scale effects of varied loading regimes can assist in the development of growth modulation methods and device designs optimized for growth plate viability preservation or mineralization stimulation based on patient age and anatomical location.

Local Changes to the Distal Femoral Growth Plate Following Injury in Mice

Injury to the growth plate is associated with growth disturbances, most notably premature cessation of growth. The goal of this study was to identify spatial changes in the structure and composition of the growth plate in response to injury to provide a foundation for developing therapies that minimize the consequences for skeletal development. We used contrast-enhanced microcomputed tomography (CECT) and histological analyses of a murine model of growth plate injury to quantify changes in the cartilaginous and osseous tissue of the growth plate. To distinguish between local and global changes, the growth plate was divided into regions of interest near to and far from the injury site. We noted increased thickness and CECT attenuation (a measure correlated with glycosaminoglycan (GAG) content) near the injury, and increased tissue mineral density (TMD) of bone bridges within the injury site, compared to outside the injury site and contralateral growth plates. Furthermore, we noted disruption of the normal zonal organization of the physis. The height of the hypertrophic zone was increased at the injury site, and the relative height of the proliferative zone was decreased across the entire injured growth plate. These results indicate that growth plate injury leads to localized disruption of cellular activity and of endochondral ossification. These local changes in tissue structure and composition may contribute to the observed retardation in femur growth. In particular, the changes in proliferative and hypertrophic zone heights seen following injury may impact growth and could be targeted when developing therapies for growth plate injury.

A review of techniques for visualising soft tissue microstructure deformation and quantifying strain Ex Vivo

Many biological tissues have a complex hierarchical structure allowing them to function under demanding physiological loading conditions. Structural changes caused by ageing or disease can lead to loss of mechanical function. Therefore, it is necessary to characterise tissue structure to understand normal tissue function and the progression of disease. Ideally intact native tissues should be imaged in 3D and under physiological loading conditions. The current published in situ imaging methodologies demonstrate a compromise between imaging limitations and maintaining the samples native mechanical function. This review gives an overview of in situ imaging techniques used to visualise microstructural deformation of soft tissue, including three case studies of different tissues (tendon, intervertebral disc and artery). Some of the imaging techniques restricted analysis to observational mechanics or discrete strain measurement from invasive markers. Full-field local surface strain measurement has been achieved using digital image correlation. Volumetric strain fields have successfully been quantified from in situ X-ray microtomography (micro-CT) studies of bone using digital volume correlation but not in soft tissue due to low X-ray transmission contrast. With the latest developments in micro-CT showing in-line phase contrast capability to resolve native soft tissue microstructure, there is potential for future soft tissue mechanics research where 3D local strain can be quantified. These methods will provide information on the local 3D micromechanical environment experienced by cells in healthy, aged and diseased tissues. It is hoped that future applications of in situ imaging techniques will impact positively on the design and testing of potential tissue replacements or regenerative therapies. LAY DESCRIPTION: The soft tissues in our bodies, such as tendons, intervertebral discs and arteries, have evolved to have complicated structures which deform and bear load during normal function. Small changes in these structures can occur with age and disease which then leads to loss of function. Therefore, it is important to image tissue microstructure in 3D and under functional conditions. This paper gives an overview of imaging techniques used to record the deformation of soft tissue microstructures. Commonly there are compromises between obtaining the best imaging result and retaining the samples native structure and function. For example, invasive markers and dissecting samples damages the tissues natural structure, and staining or clearing (making the tissue more transparent) can distort tissue structure. Structural deformation has been quantified from 2D imaging techniques (digital image correlation) to create surface strain maps which help identify local tissue mechanics. When extended to 3D (digital volume correlation), deformation measurement has been limited to bone samples using X-ray micro-CT. Recently it has been possible to image the 3D structure of soft tissue using X-ray micro-CT meaning that there is potential for internal soft tissue mechanics to be mapped in 3D. Future application of micro-CT and digital volume correlation will be important for soft tissue mechanics studies particularly to understand normal function, progression of disease and in the design of tissue replacements.