Here, we investigated the possible anti-cancer properties of bromelain in Kras mutant human colorectal carcinoma cell lines and a mouse model harboring a Kras mutation. Cell growth and proliferation were significantly reduced in the Kras mutant colorectal carcinoma cell lines following treatment with 50 μg/mL bromelain as assessed by crystal violet staining and a proliferation assay. To identify the molecules responsible for this action, the expression levels of genes involved in signaling pathways and miRNAs were analyzed by real-time PCR. Among the genes tested, down-regulation of ACSL-4 and up-regulation of miRNAs targeting ASCL-4 were observed in Caco2 cells. Compared to the Kras wild-type colorectal carcinoma cell lines, Kras mutant colorectal carcinoma cell lines exhibited a remarkably up-regulated expression of ACSL-4, which is responsible for ferroptosis sensitivity. Moreover, the knockdown of ACSL-4 by a specific shRNA inhibited erastin-induced ferroptosis in Kras mutant DLD-1 cells as assessed by propidium iodide staining and lipid reactive oxygen species measurement. Our findings indicate that bromelain effectively exerts cytotoxic effects in Kras mutant colorectal cancer cells compared to in Kras wild-type colorectal cancer cells. Differential expression of ACSL-4 is responsible for the differential action of bromelain in regulating ferroptotic cell death.

Even though increasing evidence indicates the importance of peroxisomal lipid metabolism in regulating biological and pathological events, its involvement in cartilage development has not been well studied. Here, we identified the importance of peroxisomal function, particularly the functional integrity of ABCD2, in the pathogenesis of osteoarthritis (OA). Knockdown of ABCD2 in OA chondrocytes induced the accumulation of very long chain fatty acids (VLCFAs) and apoptotic cell death. Moreover, knockdown of ABCD2 altered profiles of miRNAs that affect the expression level of ACSL4, a known direct regulator of lipid metabolism. Suppression of ACSL4 in human chondrocytes‐induced VLCFA accumulation, MMP‐13 expression, and apoptotic cell death. In vivo morph‐down of the ACSL4 homologue in zebrafish resulted in significant defects in cartilage development and in vivo knockdown of ACSL4 in cartilage tissue of an OA model mice promoted severe cartilage degradation. In summary, to the best of our knowledge, this is the first report suggesting that the regulatory network among peroxisomal ABCD2:ACSL4:VLCFA serves as a novel regulator of cartilage homeostasis, and these data may provide novel insights into the role of peroxisomal fatty acid metabolism in pathogenesis of human OA. Significance of the study Our study indicates that peroxisomal dysfunction is closely related to OA pathogenesis. Particularly, the functional integrity of ABCD2 may play an important role in OA pathogenesis via the accumulation of VLCFAs and stimulation of apoptotic death through altering profiles of miRNAs that target ACSL4. Our findings suggest that targeting the regulatory network among the peroxisomal ABCD2:ACSL4:VLCFA axis may provide a new potential therapeutic strategy for OA pathogenesis.

Studies have suggested that dysregulation of peroxisomal lipid metabolism might play an important role in colorectal cancer (CRC) development. Here, we found that KrasG12D-driven CRC tumors demonstrate dysfunctional peroxisomal β-oxidation and identified Nudt7 (peroxisomal coenzyme A diphosphatase NUDT7) as one of responsible peroxisomal genes. In KrasG12D-driven CRC tumors, the expression level of Nudt7 was significantly decreased. Treatment of azoxymethane/dextran sulfate sodium (AOM/DSS) into Nudt7 knockout (Nudt7−/−) mice significantly induced lipid accumulation and the expression levels of CRC-related genes whereas xenografting of Nudt7-overexpressed LS-174T cells into mice significantly reduced lipid accumulation and the expression levels of CRC-related genes. Ingenuity pathway analysis of microarray using the colon of Nudt7−/− and Nudt7+/+ mice treated with AOM/DSS suggested Wnt signaling as one of activated signaling pathways in Nudt7−/− colons. Upregulated levels of β-catenin were observed in the colons of KrasG12D and AOM/DSS-treated Nudt7−/− mice and downstream targets of β-catenin such as Myc, Ccdn1, and Nos2, were also significantly increased in the colon of Nudt7−/− mice. We observed an increased level of palmitic acid in the colon of Nudt7−/− mice and attachment of palmitic acid-conjugated chitosan patch into the colon of mice induced the expression levels of β-catenin and CRC-related genes. Overall, our data reveal a novel role for peroxisomal NUDT7 in KrasG12D-driven CRC development.

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