Mitochondrial genetics and osteoarthritis.

The genetic contribution is one of the most notable factors that play a main role in the risk of OA. Despite the genetics of this disease is complex and the finding of risk-related genes has been very challenging, evidence for genetic predisposition has been reported. Besides, in the last years recent evidences indicate that the mitochondrion is implicated in OA. In this context, the mtDNA haplogroups, defined as individual groups characterized by the presence of a particular set of single nucleotide polymorphisms (SNPs) in the mtDNA sequence, emerged as new genetic variants involved in this pathology. Moreover, it has been described that mtDNA damage not only accumulates in OA chondrocytes, but also that OA chondrocytes have limited mtDNA repair capacity. In this review we will focus on the influence of mitochondrial genetics and the mtDNA haplogroups in the prevalence, severity and progression of the OA disease, as well as their incidence on many OA-related features, such as serum levels of OA-related molecular markers, Nitric Oxide production or telomere length.

Mitochondrial haplogroups define two phenotypes of osteoarthritis.

OBJECTIVE: To assess a mitochondrion-related phenotype in patients with osteoarthritis (OA). METHODS: Serum levels of the following OA-related biomarkers: matrix metalloproteinase-1 (MMP-1); MMP-3; MMP-13; myeloperoxidase (MPO); a peptide of the alpha-helical region of type II collagen, Coll2-1, and its nitrated form Coll2-1NO(2); a C-terminal neoepitope generated by the collagenase-mediated cleavage of collagen type II triple helix, C2C; the C-propeptide of collagen type II, CPII; hyaluronic acid (HA); human cartilage glycoprotein 39, YKL-40; cartilage oligomeric matrix protein; and cathepsin K were analyzed in 48 OA patients and 52 healthy controls carrying the haplogroups H and J. Logistic regression models and receiver operating characteristic (ROC) curves were performed to predict the onset of OA. RESULTS: MMP-13 was the only biomarker significantly increased in OA patients compared to healthy controls in both haplogroups H and J. The collagen type II biomarkers, Coll2-1, Coll2-1NO(2), the Coll2-1NO(2)/Coll2-1 ratio, C2C, CPII, and the C2C:CPII ratio were significantly increased in OA patients carrying haplogroup H compared to OA carriers of the haplogroup J. Two logistic regression models for diagnosis were constructed and adjusted for age, gender, and body mass index. For haplogroup H, the biomarkers significantly associated with OA were MMP-13 and Coll2-1; the area under the curve (AUC) of the ROC curve for this model was 0.952 (95% CI = 0.892-1.012). For haplogroup J, the only biomarker significantly associated with OA was MMP-13; the AUC for this model was 0.895 (95% CI = 0.801-0.989). CONCLUSION: The mitochondrial DNA haplogroups are potential complementary candidates for biomarkers of OA; their genotyping in conjunction with the assessment of classical protein molecular markers is recommended.