Gut-spine axis: a possible correlation between gut microbiota and spinal degenerative diseases

Bone morphogenetic proteins, DNA methylation, and gut microbiota interaction in lumbar disc degeneration: A multi-omics Mendelian randomization study

Background

Lumbar disc degeneration (LDD) is a ubiquitous finding in low back pain. Many different etiology factors may explain the LDD process, such as bone morphogenetic proteins (BMPs), DNA methylation, and gut microbiota. Until recently the mechanisms underlying the LDD process have been elusive.

Methods

BMP-related genes were extracted from the GeneCards database. The LDD transcriptome dataset was obtained from the Gene Expression Omnibus. We used linear regression and meta-analysis to screen and integrate the differentially expressed genes associated with BMPs in LDD. Genome-wide association studies (GWASs) of LDD were from FinnGen and UKBB. The expression quantitative trait loci (eQTLs) and DNA methylation quantitative trait loci from the blood were identified via the summary data-based Mendelian randomization (SMR) method, and the possible blood BMP genes and their regulatory elements associated with the risk of LDD were prioritized. Intestinal eQTLs and fecal microbial QTLs (mbQTLs) were integrated, and the potential interactions between BMP gene expression in host intestinal tissue and the gut microbiota were revealed through SMR and colocalization analysis. The GWAS catalog (GCST90246169) was used to validate SMR results.

Results

A meta-analysis of five datasets revealed that 113 BMP genes were differentially expressed between LDD and control tissues. Seven genes were selected as candidate pathogenic genes of LDD via the three-step SMR method: CREB1, BMP6, PTCH1, GLI1, MEG3, GALNS, and NF1. SMR analysis also revealed five possible gut genes: HFE, MET, MAPK3, NPC1, and GDF5. The correlation between the gut microbiota and BMP gene expression in intestinal tissues was verified by eQTL-mbQTL colocalization.

Conclusion

This multi-omics study revealed that the BMP genes associated with LDD are regulated by DNA methylation. There are genetic differences between gut gene expression and the gut microbiota. These findings provide evidence for new therapeutic targets in the future.

A new target for treating intervertebral disk degeneration: gut microbes

Intervertebral disk degeneration (IDD) is a common clinical spinal disease and one of the main causes of low back pain (LBP). Generally speaking, IDD is considered a natural degenerative process with age. However, with the deepening of research, people have discovered that IDD is not only related to age, but also has many factors that can induce and accelerate its progression. In addition, the pathogenesis of IDD remains unclear, resulting in limited traditional treatment methods that cannot effectively prevent and treat IDD. Conservative treatment may lead to patients' dependence on drugs, and the pain relief effect is not obvious. Similarly, surgical treatment is highly invasive, with a longer recovery time and a higher recurrence rate. With the deepening of exploration, people have discovered that intestinal microorganisms are an important symbiotic microbial community in the human body and are closely related to the occurrence and development of various diseases. Changes in intestinal microorganisms and their metabolites may affect the body's inflammatory response, immune regulation, and metabolic processes, thereby affecting the health of the intervertebral disk. In this context, the gut microbiota has received considerable attention as a potential target for delaying or treating IDD. This article first introduces the impact of gut microbes on common distal organs, and then focuses on three potential mechanisms by which gut microbes and their metabolites influence IDD. Finally, we also summarized the methods of delaying or treating IDD by interfering with intestinal microorganisms and their metabolites. Further understanding of the potential mechanisms between intestinal microorganisms and IDD will help to formulate reasonable IDD treatment strategies to achieve ideal therapeutic effects.

Causal effects of specific gut microbiota on spinal stenosis diseases: a two-sample mendelian randomization study

Background

Although recent observational studies and clinical trials have indicated a strong association between the gut microbiota and spinal stenosis diseases, the causal relationship between them remains unclear.

Methods

Based on large-scale genome-wide association studies, we employed two-sample Mendelian randomization (MR) to analyse the causal relationships between the gut microbiota (GM) and 3 spinal stenosis diseases: adolescent idiopathic scoliosis (AIS), lumbar spondylolisthesis (LS), and spinal stenosis (SS). MR analysis was performed using the inverse variance weighting (IVW) method as the primary approach, supplemented by MR‒Egger regression, weighted median, and weighted mode analyses. MR-PRESSO and MR‒Egger regression were employed to assess horizontal pleiotropy. Cochran's Q test was used to evaluate heterogeneity. Further leave-one-out sensitivity analysis was conducted to ascertain the reliability of the causal relationships.

Results

The IVW method identified 9 gut microbiota taxa (9 genera) that were causally related to AIS, 14 taxa (4 phyla, 2 classes, 2 orders, 1 family, and 5 genera) to LS, and 4 taxa (2 classes, 1 order, and 1 genus) to SS. The Cochrane Q test results did not indicate heterogeneity. Moreover, both the MR‒Egger intercept test and the MR-PRESSO global test demonstrated that our findings were robust against potential horizontal pleiotropy. Furthermore, leave-one-out analysis provided additional evidence supporting the reliability of our identified causal relationships.

Conclusion

Our findings have substantiated the potential causal impact of specific GM taxa on AIS, LS, and SS, thereby offering novel insights into the mechanisms mediated by the gut microbiota in these three diseases and laying the foundation for targeted preventive measures in further research.

Microbiota-bone axis in ageing-related bone diseases

Bone homeostasis in physiology depends on the balance between bone formation and resorption, and in pathology, this homeostasis is susceptible to disruption by different influences, especially under ageing condition. Gut microbiota has been recognized as a crucial factor in regulating host health. Numerous studies have demonstrated a significant association between gut microbiota and bone metabolism through host-microbiota crosstalk, and gut microbiota is even an important factor in the pathogenesis of bone metabolism-related diseases that cannot be ignored. This review explores the interplay between gut microbiota and bone metabolism, focusing on the roles of gut microbiota in bone ageing and aging-related bone diseases, including osteoporosis, fragility fracture repair, osteoarthritis, and spinal degeneration from different perspectives. The impact of gut microbiota on bone metabolism during aging through modification of endocrinology system, immune system and gut microbiota metabolites are summarized, facilitating a better grasp of the pathogenesis of aging-related bone metabolic diseases. This review offers innovative insights into targeting the gut microbiota for the treatment of bone ageing-related diseases as a clinical therapeutic strategy.

Thick Skin on the Dorsal Spine in Osteoproliferative Disease: Ossification of the Posterior Longitudinal Ligament and Diffuse Idiopathic Skeletal Hyperostosis

Background Although the correlation between reduced skin thickness and reduced bone density has been investigated, no study has evaluated skin thickness and osteoproliferative diseases, including ossification of the posterior longitudinal ligament (OPLL) and diffuse idiopathic skeletal hyperostosis (DISH). Methodology This retrospective cohort study consisted of 99 consecutive patients aged ≥60 years treated for spinal surgery at our hospital between January 2022 and March 2023. Skin thickness was measured at the dorsal side of the cervical, thoracic, and lumbar vertebrae on the sagittal cross-section image of whole-spine CT. Based on the median value, skin thickness was categorized into two groups based on a median thickness of 4 mm. Bone mineral density (BMD) was assessed. The sum of the vertebral body and intervertebral bridging osteophytes of the anterior longitudinal and posterior longitudinal ligament were defined as the OALL index and OPLL index. Serum levels of bone metabolism-related markers, such as tartrate-resistant acid phosphatase type 5b, procollagen I N-propeptide, 25-hydroxyvitamin D, and periostin, were measured. To assess the association between skin thickness and imaging findings, we calculated the adjusted odds ratios, adjusting for age, sex, and body mass index (BMI) and using univariate and multivariate logistic regression analyses. Results No significant differences were found in skin thickness in the three dorsal regions of the cervical, thoracic, and lumbar spine (median = 3.3 mm versus 3.5 mm versus 3.4 mm, p = 0.357) and bone metabolism-related markers. Adjusting for age, sex, and BMI, cervical, thoracic, and lumbar skin thicknesses were related to DISH, the OPLL index, and the OPLL and OPLL index, respectively. Conclusions Skin thickness did not correlate with BMD but with the amount of spinal ossification. A correlation was found between skin thickness and vertebral and intervertebral ossification; vertebral osteophytes, OPLL, and DISH may be more common in thicker skin.

Association between gut microbiota and spinal stenosis: a two-sample mendelian randomization study

Introduction

Considerable evidence has unveiled a potential correlation between gut microbiota and spinal degenerative diseases. However, only limited studies have reported the direct association between gut microbiota and spinal stenosis. Hence, in this study, we aimed to clarify this relationship using a two-sample mendelian randomization (MR) approach.

Materials and Methods

Data for two-sample MR studies was collected and summarized from genome-wide association studies (GWAS) of gut microbiota (MiBioGen, n = 13, 266) and spinal stenosis (FinnGen Biobank, 9, 169 cases and 164, 682 controls). The inverse variance-weighted meta-analysis (IVW), complemented with weighted median, MR-Egger, weighted mode, and simple mode, was used to elucidate the causality between gut microbiota and spinal stenosis. In addition, we employed mendelian randomization pleiotropy residual sum and outlier (MR-PRESSO) and the MR-Egger intercept test to assess horizontal multiplicity. Cochran's Q test to evaluate heterogeneity, and "leave-one-out" sensitivity analysis to determine the reliability of causality. Finally, an inverse MR analysis was performed to assess the reverse causality.

Results

The IVW results indicated that two gut microbial taxa, the genus Eubacterium fissicatena group and the genus Oxalobacter, have a potential causal relationship with spinal stenosis. Moreover, eight potential associations between genetic liability of the gut microbiota and spinal stenosis were implied. No significant heterogeneity of instrumental variables or horizontal pleiotropy were detected. In addition, "leave-one-out" sensitivity analysis confirmed the reliability of causality. Finally, the reverse MR analysis revealed that no proof to substantiate the discernible causative relationship between spinal stenosis and gut microbiota.

Conclusion

This analysis demonstrated a possible causal relationship between certain particular gut microbiota and the occurrence of spinal stenosis. Further studies focused on the mechanism of gut microbiota-mediated spinal stenosis can lay the groundwork for targeted prevention, monitoring, and treatment of spinal stenosis.

A view on the skin-bone axis: unraveling similarities and potential of crosstalk

The phrase "skin as a mirror of internal medicine," which means that the skin reflects many of the diseases of the internal organs, is a well-known notion. Despite the phenotypic differences between the soft skin and hard bone, the skin and bone are highly associated. Skin and bone consist of fibroblasts and osteoblasts, respectively, which secrete collagen and are involved in synthesis, while Langerhans cells and osteoclasts control turnover. Moreover, the quality and quantity of collagen in the skin and bone may be modified by aging, inflammation, estrogen, diabetes, and glucocorticoids. Skin and bone collagen are pathologically modified by aging, drugs, and metabolic diseases, such as diabetes. The structural similarities between the skin and bone and the crosstalk controlling their mutual pathological effects have led to the advocacy of the skin-bone axis. Thus, the skin may mirror the health of the bones and conversely, the condition of the skin may be reflected in the bones. From the perspective of the skin-bone axis, the similarities between skin and bone anatomy, function, and pathology, as well as the crosstalk between the two, are discussed in this review. A thorough elucidation of the pathways governing the skin-bone axis crosstalk would enhance our understanding of disease pathophysiology, facilitating the development of new diagnostics and therapies for skin collagen-induced bone disease and of new osteoporosis diagnostics and therapies that enhance skin collagen to increase bone quality and density.