TNFα increases tyrosine hydroxylase expression in human monocytes

Abstract

Most, if not all, peripheral immune cells in humans and animals express tyrosine hydroxylase (TH), the rate limiting enzyme in catecholamine synthesis. Since TH is typically studied in the context of brain catecholamine signaling, little is known about changes in TH production and function in peripheral immune cells. This knowledge gap is due, in part, to the lack of an adequately sensitive assay to measure TH in immune cells expressing lower TH levels compared to other TH expressing cells. Here, we report the development of a highly sensitive and reproducible Bio-ELISA to quantify picogram levels of TH in multiple model systems. We have applied this assay to monocytes isolated from blood of persons with Parkinson’s disease (PD) and to age-matched, healthy controls. Our study unexpectedly revealed that PD patients’ monocytes express significantly higher levels of TH protein in peripheral monocytes relative to healthy controls. Tumor necrosis factor (TNFα), a pro-inflammatory cytokine, has also been shown to be increased in the brains and peripheral circulation in human PD, as well as in animal models of PD. Therefore, we investigated a possible connection between higher levels of TH protein and the known increase in circulating TNFα in PD. Monocytes isolated from healthy donors were treated with TNFα or with TNFα in the presence of an inhibitor. Tissue plasminogen activator (TPA) was used as a positive control. We observed that TNFα stimulation increased both the number of TH+ monocytes and the quantity of TH per monocyte, without increasing the total numbers of monocytes. These results revealed that TNFα could potentially modify monocytic TH production and serve a regulatory role in peripheral immune function. The development and application of a highly sensitive assay to quantify TH in both human and animal cells will provide a novel tool for further investigating possible PD immune regulatory pathways between brain and periphery.

DAT and TH expression marks human Parkinson’s disease in peripheral immune cells

“…1H ). Consistent with recent reports 20 , 67 , 68 , these data support the interpretation that dopaminergic proteins may mediate immune functions in PBMCs, and that PBMCs expressing DAT and TH may delineate PD in human patients relative to healthy controls.…”

“…In myeloid cells, dopaminergic proteins such as DAT and TH modulate immune functions and attenuate runaway inflammation 20 , 67 – 69 , 120 – 123 . For instance, DAT activity on peripheral immune cells regulates cytokine release following immune stimulation 123 .…”

“…PD patients were compared to age/sex-matched control subjects. PBMCs from patients with Parkinson’s disease and healthy control subjects were isolated by density gradient centrifugation using Ficoll-Paque and assessed by flow cytometry to detect myeloid cells expressing TH and DAT 20 , 21 , 69 , 123 , (Fig. 2B , Supplementary Fig.…”

“…Monocytes serve as front-line effector cells, and depending on the disease or injury, monocytes can adopt a range of intermediate phenotypes from pro-inflammatory to anti-inflammatory 53 , 54 . Importantly, PBMC-derived monocytes express an entire complement of dopaminergic signaling machinery: TH, vesicular monoamine transporter (VMAT2), dopamine receptors (DRD1-DRD5) and dopamine transporters (DATs) 20 , 47 , 55 – 62 . Immune cells’ dopamine receptor expression and function have been implicated in PD and PD-like neurodegeneration 63 – 66 .…”

α-Synuclein-induced dysregulation of neuronal activity contributes to murine dopamine neuron vulnerability

“…2 and 3 ) leads to increased TH levels that can contribute to increased intracellular dopamine 80 , 82 – 87 . Since the frequently used approaches of western blotting or ICC do not provide purely quantitative data of protein expression to test this hypothesis, we developed an enzyme-linked immunosorbent assay (ELISA) 88 to quantify TH levels in α-syn-overexpressing neurons (Fig. 4i ).…”