Panoply™ Human HRH4 Knockdown Stable Cell Line

Diabetic patients have elevated systemic histaminergic activity. A few studies have implicated histamine in the pathogenesis of diabetes, but its precise role in the development of diabetic retinopathy remains unclear. Here, researchers investigated the role of histamine receptor H4 (HRH4) in regulating retinal pigment epithelium (RPE)-derived pro- and anti-angiogenic factors under diabetic conditions. Studies have shown that serum and vitreous levels of VEGF, IL-6, histamine, and HDC are higher in patients with diabetic retinopathy than in non-diabetic subjects. HRH4 is overexpressed in RPE both in vivo and in vitro. In ARPE-19 cells cultured under hyperglycemic conditions, histamine treatment upregulates VEGF and IL-6 expression and downregulates PEDF expression. Hyperglycemia-induced p38 phosphorylation, and the consequent upregulation of VEGF and IL-6 and downregulation of PEDF, were inhibited by small interfering RNA-mediated knockdown of HRH4 in ARPE-19 cells. In summary, HRH4 is a key regulator of VEGF, IL-6, and PEDF in RPE under hyperglycemic conditions, and the p38 mitogen-activated protein kinase pathway mediates this regulatory mechanism.

In ARPE-19 cells cultured in high-glucose medium, VEGF and IL-6 levels were higher than in cells grown in osmotic-controlled medium. Histamine supplementation enhanced the high-glucose-induced transcriptional upregulation of VEGF and IL-6 in ARPE-19 cells (Figure 1A, B). Conversely, PEDF expression was downregulated in ARPE-19 cells exposed to high-glucose medium, and the fold change in PEDF expression between the high-glucose and osmotic-controlled groups increased after histamine supplementation (Figure 1C). Next, to determine the role of HRH4 in amplifying the high-glucose-mediated upregulation of VEGF and IL-6 and downregulation of PEDF in histamine-induced ARPE-19 cells, HRH4 was silenced in ARPE-19 cells using siRNA. In HRH4 knockdown ARPE-19 cells treated with histamine, VEGF and IL-6 expression was significantly suppressed (Figure 1D, E). Notably, HRH4 knockdown suppressed histamine-induced transcription of VEGF and IL-6 in both the high-glucose and osmotic-controlled groups. Furthermore, the downregulation of PEDF expression was ameliorated in HRH4-knockdown ARPE-19 cells cultured under high glucose conditions (Figure 1F).

Figure 1. Role of HRH4 in modulating the expression of pro-angiogenic and anti-angiogenic factors in ARPE-19 cells. (Lee B J, et al., 2020)