Project description:Asporin, also known as periodontal ligament-associated protein 1 (PLAP1), is a member of the family of small leucine-rich proteoglycan (SLRP) family. It is present within the cartilage extracellular matrix (ECM), and is reported have a genetic association with osteoarthritis. Its D14 allele has recently been found to be associated with lumbar disc degeneration in Asian subjects. There have been no studies, however, of this gene’s normal immunohistochemical localization within the human intervertebral disc, nor of expression levels in Caucasian individuals with disc degeneration. Studies were approved by our human subjects Institutional Review Board. Methods included immunohistochemical localization of asporin in the disc of humans and the sand rat (a small rodent with spontaneous age-related disc degeneration), and Affymetrix microarray analysis of asporin gene expression in vivo and in vitro. mmunohistochemical studies of human discs revealed that some, but not all, cells of the outer annulus expressed asporin. Fewer cells in the inner annulus contained asporin, and it was rarely present in cells in the nucleus pulposus. Similar patterns were found for the presence of asporin in lumbar discs of sand rats. Substantial relative gene expression levels were seen for asporin in both disc tissue and in annulus cells grown in three-dimensional culture. More degenerate human discs (Thompson grade 4) showed higher expression levels of asporin than did less degenerate (grade 1, 2 and 3) discs, p = 0.004. In the discs of Caucasian subjects studied here, and in the sand rat, greater immunolocalization levels were found in the outer compared to inner annulus. Localization was rare in the nucleus. Gene expression studies showed greatest expression of asporin in the more degenerate human discs in vivo. Disc Tissue samples were obtained via the National Cancer Institute Cooperative Tissue Network (CHTN) as well as surgical disc procedures performed on patients with herniated discs and degenerative disc disease. Tissue was fixed and paraffin embedded. Standard laser capture microdissection (LCM) techniques were used to collect the cells from which total RNA was isolated and analyzed via microarray. Based on the Thompson scouring system, unhealthy discs (grade 4) were compared to healthy discs (grades 2,3).

Project description:Purpose: Degenerative changes of the intervertebral disc are a leading cause of back pain and disability worldwide. However, precise mechanisms driving the initiation and progression of pathology have remained elusive. We find that adhesion G-protein coupled receptor Adgrg6 plays a critical role in maintaining postnatal intervertebral disc homeostasis. The goal of this study is to uncover early molecular changes in Adgrg6-defeicnet intervertebral discs prior to overt histopathology. Methods: Intervertebral disc mRNA profiles of 20-day-old wild type and Col2Cre; Adgrg6f/f mutant mice were generated by deep sequencing in triplicates. Cutadapt and perl scripts were used to remove the reads that contained adaptor contamination, low quality bases and undetermined bases. Then sequence quality was verified using FastQC. We used HISAT2 to map reads to the genome of Mus Musculus (GRCm38.88). The mapped reads of each sample were assembled using StringTie. Then, all transcriptomes from biological samples were merged to reconstruct a comprehensive transcriptome using perl scripts and gffcompare. After the ﬁnal transcriptome was generated, StringTie and Ballgown was used to estimate the expression levels of all transcripts. StringTie was used to perform expression level for mRNAs by calculating FPKM. The differentially expressed mRNAs were selected with log2 (fold change) >1 or log2 (fold change) <-1 and with statistical significance (p value < 0.05) by R package Ballgown. Results: We found 884 differential expressed genes with statistical significance (p value < 0.05, and with a more stringent cut-off adjusted p value <0.05 and fold-change >2, we observed 42 differential expressed genes. Enriched pathways and biological processes using gene ontology (GO) terms included extracellular matrix, positive regulation of fibroblast proliferation, extracellular matrix structural constituent conferring tensile strength, regulation of tyrosine phosphorylation of STAT protein, and ion transport. We also find significantly increased expression of fibrotic collagens, induced expression of some Suppressor of Cytokine Signaling (SOCS) genes, and dysregulated expression of some components associated with ion transport system. Several of the significantly upregulated genes are associated with biomarkers or risk of lumbar disc degeneration and osteoarthritis in humans or animal models. Conclusions: Our study provides detailed analysis of intervertebral disc transcriptomes from both wild type and Adgrg6-deficient mice, with three biological replicates, prior to overt histopathology. Our transcriptomic analysis demonstrated a robust dysregulation of several important pathways and components of the intervertebral disc homeostasis, including induction of fibrotic gene expression, alteration of ion transport component, as well as changes in some chondrogenic and catabolic factors, prior to the onset of histopathology and disc degeneration. These data strongly suggest that ADGRG6 signaling is a critical factor for the maintenance of healthy gene expression profiles in the IVD.

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Homo sapiens

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