The Deregulated Autophagy of Mitochondria May Be Involved in the Pathogenesis in Primary Biliary Cirrhosis
Motoko Sasaki, Masami Miyakoshi, Yasunori Sato, Yasuni Nakanuma. Kanazawa University Graduate School of Medicine, Kanazawa, Japan
Background: We have reported the deregulated autophagy and following cellular senescence characterize the biliary epithelial lesions in primary biliary cirrhosis (PBC). Although it is well known that serum anti-mitochondrial antibodies (AMAs) are detected in most patients with PBC, the significance of AMAs in the pathogenesis of PBC has not been fully clarified, so far. Since mitochondria are major targets of autophagy, we hypothesized that the deregulated autophagy of mitochondria may be related to the autoimmune pathogenesis in PBC.
Design: We examined immunohistochemically the expression of pyruvate dehydrgenase complex-E2 component (PDC-E2), a major target of AMAs, in livers taken from the patients with PBC (n=42) and control livers (n=77) including primary sclerosing cholangitis (PSC) and normal livers. We examined the co-localization of PDC-E2 with microtubule-associated proteins-light chain 3b (LC3), an autophagy marker, p62/sequestosome-1 (p62), a deregulated autophagy marker, and lysosomal-associated membrane protein 1 (LAMP-1) by double immunofluorescence. We also examined the co-localization of PDC-E2 with autophagy-related markers LC3, p62 and LAMP-1 in cultured mouse biliary epithelial cells (BECs) treated with various stress, such as H2O2 (100μM, 2hr), and serum deprivation with and without lysosome inhibitor bafilomycin A.
Results: The expression of PDC-E2 was absent or faint in BECs in small bile ducts in control livers. In contrast, an intense granular and vesicular expression of PDC-E2 was seen in small bile ducts in PBC, especially in the damaged ones. The granular and vesicular expression of PDC-E2 was significantly more frequent in small bile ducts in PBC, compared with control livers (p<0.01). The expression of PDC-E2 was co-localized with LC3 and partly with LAMP-1 in the damaged bile ducts in PBC. The locolization of PDC-E2 and p62 was different and not co-localized in BECs in PBC. In cultured BECs, the number of LC3-positive autophagic vacuoles was significantly more increased, when treated with various stress (p<0.01). The co-localization of PDC-E2 with LC3-punctae, suggesting the autophagy of mitochondria, was seen in BECs treated with various stress, especially in BECs treated with serum deprivation and bafilomycin A.
Conclusions: The granular and vesicular expression of PDC-E2 was increased in biliary epithelial lesions in PBC and closely related to the deregulated autophagy. The abnormal expression of PDC-E2 associated with deregulated autophagy may be related to the autoimmune mechanism directed to PDC-E2 in PBC.
Monday, March 19, 2012 2:30 PM
Platform Session: Section E, Monday Afternoon