Alterations in expression of p11 and SERT in mucosal biopsy specimens of patients with irritable bowel syndrome

Abstract

Background & aims: The pathophysiology of irritable bowel syndrome (IBS) remains enigmatic; abnormalities in serotonin metabolism have been implicated. Two proteins that influence the function of serotonin and serotonergic receptors are serotonin transporter protein (SERT or soluble carrier protein, SLC6A4) and p11 (S-100A10, or calpactin I light chain). Both proteins are reported to be associated with depression-like states, a frequent comorbid condition in IBS. We explored the hypothesis that expression of these 2 proteins in colonic and rectal mucosa is abnormal in patients with IBS as compared with healthy controls.

Methods: Messenger RNA (mRNA) expression of SLC6A4 and p11 was measured in sigmoid and rectal mucosal biopsy specimens. Genotype of the promoter for SLC6A4 was also assessed in all participants. Validation studies explored reproducibility of 2 biopsy specimens taken from the same region and biopsy specimens taken an average of approximately 3 months apart.

Results: We found normal colonic mucosal expression of SLC6A4 in diarrhea (IBS-D)- or constipation-predominant IBS (IBS-C). On the other hand, p11 expression was increased in IBS. No significant effect on p11 mRNA expression in sigmoid colon or rectum was noted from antidepressant treatment in any of the analyzed subgroups.

Conclusions: Colonic mucosal expression of SLC6A4 in IBS is normal. Given that overexpression of p11 can increase serotonergic receptor functions (eg, 5-HT(1B) receptors), these data support the need for further study of the interaction between p11 expression in health and disease and its role in the therapeutic response to serotonergic agents, including antidepressants.

Figure 1

Relative SLC6A4 mRNA expression in mucosal biopsies from (A) sigmoid colon and (B) rectum in healthy controls, IBS-D and IBS-C patients. Filled circles refer to participants receiving antidepressant medications. Data are expressed relative to the control genes SART1 (left) and ACTB (right). For sigmoid colon, data points represent the average value of two samples per subject. Median values per group are shown as horizontal lines.

Figure 2

Bland-Altman plots of the relative SLC6A4 mRNA expression level in two sigmoid biopsies taken at the same sigmoidoscopy in controls and IBS. Data are expressed relative to the control genes SART1 (left) and ACTB (right). Units of both axes are fold difference of SLC6A4 over control gene. Dashed lines represent the 95% confidence intervals for the mean difference between the biopsies.

Figure 3

Bland-Altman plots of the relative SLC6A4 mRNA expression level within 10 subjects (5 controls and 5 IBS) in rectal and sigmoid colon mucosal biopsies over time. Median time between endoscopies was 82 days. Data are expressed relative to the control genes SART1 (top row) and ACTB (bottom row). Units of both axes are fold difference of SLC6A4 over control gene. The averaged values from the initial two sigmoid biopsies were used for this analysis.

Figure 4

Comparison of mucosal SLC6A4 mRNA expression between SLC6A4 promoter genotypes. Data of SLC6A4 mRNA are expressed in relation to the control genes SART1 (upper panel) and ACTB (lower panel). Results from sigmoid and rectal biopsies are shown on the left and right, respectively. Horizontal lines represent medians.

Figure 5

S100A10 (p11) mRNA expression in mucosal biopsies from (A) sigmoid colon and (B) rectum in healthy controls and IBS-D and IBS-C patients based on two different RTQ-PCR TaqMan assays (p11 exon 1–2 and p11 exon 2–3). Filled circles refer to participants receiving antidepressant medications. Data are expressed relative to the control gene B2M. For sigmoid colon, data points represent the average value of two samples per subject. Median values per group are shown as horizontal lines. Asterisks represent p-values <0.05 (*) or <0.01 (**) in two-group comparisons following significant Kruskal-Wallis tests.