Iron regulatory proteins 1 and 2 have opposing roles in regulating inflammation in bacterial orchitis

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Abstract

Acute bacterial orchitis (AO) is a prevalent cause of intrascrotal inflammation, often resulting in sub- or infertility. A frequent cause eliciting AO is uropathogenic Escherichia coli (UPEC), a gram negative pathovar, characterized by the expression of various iron acquisition systems to survive in a low-iron environment. On the host side, iron is tightly regulated by iron regulatory proteins 1 and 2 (IRP1 and -2) and these factors are reported to play a role in testicular and immune cell function; however, their precise role remains unclear. Here, we showed in a mouse model of UPEC-induced orchitis that the absence of IRP1 results in less testicular damage and a reduced immune response. Compared with infected wild-type (WT) mice, testes of UPEC-infected Irp1–/– mice showed impaired ERK signaling. Conversely, IRP2 deletion led to a stronger inflammatory response. Notably, differences in immune cell infiltrations were observed among the different genotypes. In contrast with WT and Irp2–/– mice, no increase in monocytes and neutrophils was detected in testes of Irp1–/– mice upon UPEC infection. Interestingly, in Irp1–/– UPEC-infected testes, we observed an increase in a subpopulation of macrophages (F4/80+CD206+) associated with antiinflammatory and wound-healing activities compared with WT. These findings suggest that IRP1 deletion may protect against UPEC-induced inflammation by modulating ERK signaling and dampening the immune response.

Authors

Niraj Ghatpande, Aileen Harrer, Bar Azoulay-Botzer, Noga Guttmann-Raviv, Sudhanshu Bhushan, Andreas Meinhardt, Esther G. Meyron-Holtz