Osteopontin (OPN) is a bone-derived phosphoglycoprotein related to physiological and pathological mechanisms that nowadays has gained relevance due to its role in the immune system response to chronic degenerative diseases, including rheumatoid arthritis (RA) and osteoarthritis (OA). OPN is an extracellular matrix (ECM) glycoprotein that plays a critical role in bone remodeling. Therefore, it is an effector molecule that promotes joint and cartilage destruction observed in clinical studies, in vitro assays, and animal models of RA and OA. Since OPN undergoes multiple modifications, including posttranslational changes, proteolytic cleavage, and binding to a wide range of receptors, the mechanisms by which it produces its effects, in some cases, remain unclear. Although there is strong evidence that OPN contributes significantly to the immunopathology of RA and OA when considering it as a common denominator molecule, some experimental trial results argue for its protective role in rheumatic diseases. Elucidating in detail OPN involvement in bone and cartilage degeneration is of interest to the field of rheumatology. This review aims to provide evidence of the OPN’s multifaceted role in promoting joint and cartilage destruction and propose it as a common denominator of AR and OA immunopathology.

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a severe complication associated with the neurotoxic effects of circulating autoantibodies in the central nervous system (CNS) manifested frequently as a learning and memory deficit. Pristane-induced lupus in BALB/c female mice is an experimental model that resembles some clinical and immunological SLE pathogenesis associated with environmental factors. Nevertheless, there is no experimental evidence that relate pristane-induced lupus with cognitive dysfunction associated with autoantibodies production. Objective: To evaluate cognitive impairment related to memory deficits in a pristane-induced lupus BALB/c female mice related to mRNA expression levels of NR2A/2B hippocampal subunits in short and long-term memory task at 7 and 12 weeks after LPS exposition (7wLPS and 12wLPS) in a behavioral test with the employment of Barnes maze. Methods: Fifty-four female BALB/c mice of 8-12 weeks old were included in 2 experimental groups: 7 and 12 weeks after lypopolissacharide (LPS) exposure and classified in subgroups (control, pristane and pristane+LPS). To determine cognitive dysfunction, mice were tested in a Barnes maze. Serum anti-Sm antibodies and relative expression of hippocampal NR2A/NR2B subunits were quantified. Results: Pristane and pristane+LPS mice showed a prolonged escape latency at 7wLPS than at 12wLPS in short-term memory. Downregulation of hippocampal NR2A subunit was more evident than NR2B in pristane and pristane+LPS at 7wLPS and 12wLPS. The anti-Sm autoantibodies levels correlate with the relative expression of NR2A. Conclusion: Downregulation of hippocampal NR2A/2B subunits in the pristane-model of lupus in BALB/c mice may be related to anti-Sm autoantibodies production with the consequence of cognitive impairment in early stages of autoimmune disease.