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Evidence suggests the existence of an intracardiac dopaminergic system that plays a pivotal role in regulating cardiac function and fibrosis through G-protein coupled receptors, particularly mediated by dopamine receptor 3 (D3R). However, the expression of dopamine receptors in cardiac tissue and their role in cardiac fibroblast function is unclear. In this brief report, first we determined expression of D1R and D3R both in left ventricle (LV) tissue and fibroblasts. Then, we explored the role of D3R in the proliferation and migration of fibroblast cell cultures using both genetic and pharmaceutical approaches; specifically, we compared cardiac fibroblasts isolated from LV of wild type (WT) and D3R knockout (D3KO) mice in response to D3R-specific pharmacological agents. Finally, we determined if loss of D3R function could significantly alter LV fibroblast expression of collagen types I (Col1a1) and III (Col3a1). Cardiac fibroblast proliferation was attenuated in D3KO cells, mimicking the behavior of WT cardiac fibroblasts treated with D3R antagonist. In response to scratch injury, WT cardiac fibroblasts treated with the D3R agonist, pramipexole, displayed enhanced migration compared to control WT and D3KO cells. Loss of function in D3R resulted in attenuation of both proliferation and migration in response to scratch injury, and significantly increased the expression of Col3a1 in LV fibroblasts. These findings suggest that D3R may mediate cardiac fibroblast function during the wound healing response. To our knowledge this is the first report of D3R's expression and functional significance directly in mouse cardiac fibroblasts.

Dopamine is a neurotransmitter heavily involved in neural pathways regulating the reward response, body movement, mood, and cognitive function. As such, much of the research on dopamine and its five receptor subtypes has been conducted to observe the in vivo function of each receptor subtype in neurological disorders. However, recent studies by colleagues from our institution have suggested that D3Rs may play a role in cardiac‐related aging, as 2‐month old D3 receptor knock‐out (D3KO) mice show age‐related changes in cardiac function similar to 2‐year old wild‐type (WT) mice. Thus, it would be interesting to understand the role of D3R expression in LV cardiac fibroblast and its function. We isolated, cultured and characterized cardiac fibroblasts from the left ventricles (LV) of WT (23‐weeks old) and D3KO (5 and 31‐week‐old) mice. Immunohistochemistry was performed to determine the expression of D3R in LV cardiac fibroblasts, and cell culture experiments were performed to examine possible changes in WT and D3KO cell migration and proliferation. Proliferation was measured via total cell count over time points of 6, 12, 24, and 36 hours, while migration in response to scratch wound was examined as percent change in area at 3, 6, 12, 24 hours, and every 12 hours thereafter up to 86 hours. Staining with antibodies for D3R successfully showed expression of this receptor in WT fibroblasts, while cell culture experiments showed reduced proliferation and migration of D3KO fibroblasts compared to WT. Migration of D3KO fibroblasts from 5‐week old mice were significantly different (*p<0.05) in response to an artificial wound when compared to 23‐week‐old mice. Additionally, upon isolation of LV cardiac fibroblasts from 5‐week‐old and 31‐week‐old D3KO and 23‐week‐old WT mice, cell volume from D3KO fibroblast isolation was markedly reduced compared to WT isolation under identical conditions (5‐fold and 10‐fold decrease in 5‐week and 31‐week D3KO, respectively). This data suggests that D3Rs play a role in LV cardiac fibroblast migration and proliferation and support previous observations of age‐related changes in cardiac function of D3KO mice.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.