gms | German Medical Science

Objectives: Mesenchymal stem cells (MSCs) have been shown to play an important role in cartilage repair due to their high proliferative and chondrogenic potential. In addition, their number is increased in human osteoarthritic (OA) knee articular cartilage but the reason for this phenomenon is unknown. Sympathetic nerve fibers are present in various joint tissues and the sympathetic neurotransmitter norepinephrine (NE) was detected in the synovial fluid of trauma and OA patients. NE inhibits trauma bone marrow-derived MSCs (trauma-BMSCs) chondrogenesis and might therefore play a role in OA pathogenesis. However, the effects of NE on BMSC proliferation have not yet been analyzed. The present study was initiated to compare the effect of NE on the proliferation of trauma- and OA-BMSCs.

Methods: BMSCs were isolated from the bone marrow of trauma and OA patients (both n=5). Gene expression of adrenergic receptors was analyzed by RT-PCR (α1A-, α1B-, α1D-, α2A-, α2B-, α2C-, β1-, β2- and β3- adrenergic receptors). Cells were treated with NE in different concentrations (10^-9 to 10^-5 M), the specific β2-adrenergic receptor agonist formoterol (10^-7 M) and the specific α2-adrenergic receptor agonist UK14,304 (10^-8 M) in monolayer culture for 7 days under physioxic conditions (2% O₂, 5% CO₂). On day 7, cells were counted and cell viability was determined by measuring LDH activity.

Results and conclusion: Both trauma- and OA-BMSCs express a subset of adrenergic receptors (α1A-, α1B-, α2A-, α2B-, α2C- and β2-adrenergic receptors). Expression of both α1-receptors was higher in trauma- compared to OA-BMSCs. In contrast, OA-BMSCs showed higher expression of α2-receptors compared to t-BMSCs. Treatment with NE in high concentrations (10^-5 and 10^-6 M) as well as formoterol inhibited the proliferation of both trauma- and OA-BMCSs significantly and to the same extent compared to untreated controls. NE in low concentrations or UK14,304 did not influence BMSC proliferation. Cell viability was not affected by any treatment. Our results demonstrate that, depending on its concentration, the sympathetic neurotransmitter NE plays an important role in the proliferation of BMSCs. While high NE concentrations (10^-7 to 10^-5 M) and formoterol act via β-adrenergic receptors, low NE concentrations (10^-9 to 10^-8 M) and UK14,304 bind to α-adrenergic receptors. Therefore, effects of NE on BMSC proliferation are mediated by the β2-adrenergic receptor. This is an interesting starting point for future studies focusing on downstream signaling (ERK1/2- and PKA-pathway). Targeting β2-signaling might provide novel therapeutic options in OA treatment.