**5.2 Biological significances of α-amylase expressed in the duodenum**

α-Amylase has been shown to be expressed by tissues other than the pancreas and salivary glands, but the biological significance has not been elucidated. The increased α-amylase expression in obese mouse liver suggests that liver α-amylase may be a biomarker for obesity [34]. It has been hypothesized that α-amylase expressed in the brain may be an energy source in Alzheimer's disease [3]. Here, it was shown that the expression of α-amylase by Caco-2 cells was suppressed by RNA interference (RNAi), and affected cell proliferation and differentiation [33]. The expression of α-amylase was suppressed to about 30% by siRNA (small interfering RNA), and four kinds of cell differentiation markers were quantified by real-time PCR. All four differentiation markers were reduced in cells transfected with α-amylase siRNA compared to cells transfected with control siRNA (**Figure 9A**). This result indicates that α-amylase expression is required for cell differentiation. Furthermore, it was shown that the cell proliferation of cells transfected with α-amylase siRNA was dramatically reduced depending on the cell-seeding concentration (**Figure 9B**).
