Impairment of electroneutral Na⁺transport and associated downregulation of NHE3 contributes to the development of diarrhea following in vivo challenge withBrachyspiraspp.

Abstract

The effect of Brachyspira hyodysenteriae and Brachyspira hampsonii spirochetosis on Na+ transport was assessed in the colon to determine its contribution to diarrheal disease in pigs following experimental infection. Electrogenic and electroneutral Na+ absorption was assessed in Ussing chambers by radiolabeled 22Na flux and pharmacological inhibitory studies. Basal radiolabeled 22Na flux experiments revealed that mucosal-to-serosal flux ( Jms) was significantly impaired in B. hyodysenteriae and B. hampsonii-diseased pigs. Inhibition of epithelial sodium channel via amiloride did not significantly reduce electrogenic short-circuit current ( Isc) in the proximal, apex, and distal colonic segments of diseased pigs over control pigs, suggesting that a loss of electroneutral Na+ absorption is responsible for diarrheal development. These findings were further supported by significant downregulation of Na+/H+ exchanger (NHE1, NHE2, and NHE3) mRNA expression in the proximal, apex, and distal colonic segments paired with decreased protein expression of the critical NHE3 isoform. The decrease in NHE3 mRNA expression appears not to be attributed to the host’s cytokine response as human IL-1α did not modify NHE3 mRNA expression in Caco-2 cells. However, a whole cell B. hampsonii lysate significantly downregulated NHE3 mRNA expression and significantly increased p38 phosphorylation in Caco-2 cells. Together these findings provide a likely mechanism for the spirochete-induced malabsorptive diarrhea, indicated by a decrease in electroneutral Na+ absorption in the porcine colon due to Brachyspira’s ability to inhibit NHE3 transcription, resulting in diarrheal disease. NEW & NOTEWORTHY This research demonstrates that diarrheal disease caused by two infectious spirochete spp. is a result of impaired electroneutral Na+ absorption via Na+/H+ exchanger 3 (NHE3) in the porcine colon. Our findings suggest that the decrease in NHE3 mRNA and protein is not likely a result of the host’s cytokine response. Rather, it appears that these two Brachyspira spp. directly inhibit the transcription and translation of NHE3, resulting in the development of diarrhea.

Gut-associated cGMP mediates colitis and dysbiosis in a mouse model of an activating mutation in GUCY2C

“…Parathyroid hormone–induced inhibition of Nhe3 transcription in opossum kidney proximal tubule cells was mediated by enhanced Egr-1 binding to the core Nhe3 promoter and activation of JAK-STAT3 activity ( Neri et al, 2015 ). A recent study indicated that p38 activation in human colonic Caco2 cells was correlated with a reduction in Nhe3 transcription ( Enns et al, 2020 ). We showed earlier that PKGII activates p38, which in turn results in the increased recruitment of Sp1 to the p21 promoter, resulting in enhanced p21 transcription ( Basu et al, 2014 ).…”

Human intestinal spirochetosis, a sexually transmissible infection? Review of six cases from two sexually transmitted infection centres in Barcelona

“…5,6 The development of diarrhoeal disease in pigs may be caused by Brachyspira hyodysenteriae and Brachyspira hampsonii, as a result of the inhibition of the transcription and translation of Na þ /K þ exchanger 3. 23 This is the reason why, persistent chronic diarrhoea (for more than 4 weeks) is the most common clinical presentation of HIS, when it is symptomatic. 2,4,6,7,19,20,[24][25][26] Other possible manifestations of HIS are constipation, alternating diarrhoea and constipation, abdominal pain, blood in the stools, vomiting or nausea, anal discharge, mucus in the stools, appendicitis-like symptoms, inflammatory reactions (crypt abscesses and ulcers) or spirochetemia (mainly in immunosuppressed patients).…”

Brachyspira hyodysenteriae Infection Reduces Digestive Function but Not Intestinal Integrity in Growing Pigs While Disease Onset Can Be Mitigated by Reducing Insoluble Fiber

“…Few studies have evaluated intestinal barrier permeability, digestive function, and intestinal metabolism in B. hyodysenteriaechallenged pigs. Further, as B. hyodysenteriae is a large intestinal pathogen, investigations have been primarily limited to the cecum and colon (5,8,9). However, as the small intestine is the primary site of nutrient digestion and absorption (10), understanding if B. hyodysenteriae infection alters small intestinal integrity and function is highly relevant and applicable to developing mitigation strategies.…”