Differential tissue-specific damage caused by bacterial epididymo-orchitis in the mouse

Abstract

Ascending bacterial urinary tract infections can cause epididymo-orchitis. In the cauda epididymidis, this frequently leads to persistent tissue damage. Less coherent data is available concerning the functional consequences of epididymo-orchitis on testis and caput epididymidis. This in vivo study addresses the functional and spatial differences in responsiveness of murine epididymis and testis to infection with uropathogenic Escherichia coli (UPEC). Whole transcriptome analysis (WTA) was performed on testis, caput, corpus and cauda epididymidis of adult C57BL/6 J wildtype mice. Following UPEC-induced epididymo-orchitis in these mice, epididymal and testicular tissue damage was evaluated histologically and semi-quantitatively at 10 days and 31 days post-inoculation. Expression of inflammatory markers and candidate antimicrobial genes were analysed by RT-qPCR. WTA revealed distinct differences in gene signatures between caput and cauda epididymidis, particularly amonst immunity-related genes. Cellular and molecular signs of testicular inflammation and disruption of spermatogenesis were noticed at day 10, but recovery was observed by day 31. In contrast to the cauda, the caput epididymidis did not reveal any signs of gross morphological damage or presence of pro-inflammatory processes despite confirmed infection. In contrast to beta-defensins, known UPEC-associated antimicrobial peptides (AMP), like Lcn2, Camp and Lypd8, were inherently highly expressed or upregulated in the caput following infection, potentially allowing an early luminal protection from UPEC. At the time points investigated, the caput epididymidis was protected from any obvious infection/inflammation-derived tissue damage. Studies addressing earlier time-points will conclude whether in the caput epididymidis a pro-inflammatory response is indeed not essential for effective protection from UPEC.

Pathomechanisms of Autoimmune Based Testicular Inflammation

“…In EAO mice, the epididymis underwent a region-specific immune response positively correlating to the severity of orchitis (28,84). Similar to the observed differential immune responsiveness in a model of acute bacterial epididymitis (85,86), the distally located cauda epididymidis and vas deferens show a severe immune reaction in EAO mice characterized by an upregulated expression of cytokines and immunomodulatory factors (Tgfb1, Ccl2, Il1b, Il10, Tnf, Foxp3, Ido1), immune cell infiltration, fibrosis and epithelial damage resulting in a loss of tissue integrity and subsequent aggregation of displaced spermatozoa within the interstitium (84). The proximal regions (initial segment and caput), in contrast, do not reveal histopathological alterations or an upregulated expression of cytokines, although these regions are more densely vascularized and harbor a high number of resident immune cells (87,88).…”

Immune Cell Subtypes and Their Function in the Testis

“…Similarly, following E. coli -induced epididymo-orchitis, inflammation in the testis quickly resolves after the initial infiltration of immune cells and impairment of spermatogenesis. However, without therapeutic intervention, inflammation of the epididymis continues to remain ( 35 ). These observations suggest that the testis has a remarkable ability to resolve inflammation via mechanisms likely involving TM.…”

Differential Immune Response to Infection and Acute Inflammation Along the Epididymis

“…Emerging evidence on cellular and molecular levels has resulted in the hypothesis that the epididymis is “a series of organs side-by-side” ( 9 ). This hypothesis is evidenced by particular region-specific characteristics in regards to (a) the composition of the epithelium ( 4 , 5 ), (b) the distribution and phenotype of resident immune cells subpopulations ( 10 – 13 ), and (c) differential gene expression profiles ( 1 , 2 , 14 , 15 ). In line with that, septae segregate different segments and have been demonstrated to function as diffusion barriers, possibly creating distinct interstitial microenvironments ( 16 , 17 ).…”

“…Various in vivo and in vitro models have clearly pointed to striking region-specific differences in the epididymal immune response. The clearest observation is that the cauda epididymidis is much more sensitive to inflammatory-inflicted damage than the caput epididymidis [ Figure 1D ( 14 , 34 , 35 )]. These observations are complemented by data from patients with acute bacterial epididymitis where in most cases the cauda is predominantly impacted, particularly in severe cases when an abscess is diagnosed ( 36 ).…”

“…After infection, fundamentally disparate immune responses and associated immunopathologies were observed in different epididymal regions ( Figures 1C, D ). The caput epididymidis remains mostly unaffected throughout the course of infection despite the presence of bacteria and the expression of signaling molecules required to sense bacteria and mount inflammatory responses against them [see Region-Specific Immune Responses to LPS-Induced Epididymitis ( 14 , 34 )]. Similar region-specific immune reactions have also been observed in a mouse model of experimental autoimmune epididymo-orchitis ( 35 ).…”