Beta‐catenin inhibition as a novel therapeutic strategy for porphyria

Abstract

Background– The porphyrias are metabolic disorders caused by enzymatic defects in heme biosynthesis, leading to excessive accumulation of porphyrins and their precursors in the liver or bone marrow, the most active tissues in heme biosynthesis. The specific patterns of accumulation of the heme precursors aminolevulinic acid (ALA) and other intermediate compounds define clinical features of these diseases such as acute neurovisceral attacks, skin lesions, and mental changes. These debilitating diseases remain incurable, and there is an unmet need to develop effective therapies to treat them. Because the liver is either a source or sink for porphyrins, we investigated the role of Wnt/beta‐catenin pathway in this disease. Wnt/beta‐catenin signaling is an evolutionarily conserved pathway that plays an important role in liver health and pathophysiology by regulating genes important in metabolism and proliferation.Methods– 3,5‐Diethoxycarbonyl‐1,4‐dihydrocollidine (DDC) induces hepatic porphyria in mice and is utilized to identify signaling pathways involved in injury progression. The metabolism of DDC creates a potent inhibitor of ferrochelatase (FC), the terminal enzyme in the heme pathway, which causes the buildup of porphyrin precursors. These precursors can cause cellular abnormalities such as oxidative stress, mitochondrial dysfunction, protein aggregation and inhibition of crucial functions such as autophagy. We studied pharmacological inhibition of Wnt/beta‐catenin signaling by utilizing a beta‐catenin DsiRNA formulated into a lipid nanoparticle in mice fed DDC diet.Results– Our data demonstrates that mice with pharmacologically inhibited beta‐catenin have decreased liver injury due to significantly fewer porphyrin deposits. This is due to suppression of ALA‐S and ALA‐D enzymes which catalyze the first and second steps of heme biosynthesis respectively. Significantly, we identified a strong TCF4 binding site in the intron region of the Alad gene, implicating ALA‐D as a direct Wnt/beta‐catenin target. Our data, therefore, establishes a novel role of the Wnt/beta‐catenin pathway in regulating heme biosynthesis by inhibiting early steps in heme biosynthesis pathway and reducing toxic porphyrin accumulation. Furthermore, our data reveal that mice lacking beta‐catenin have increased induction of autophagy over baseline that contributes to the protection from injury by clearing accumulated toxic porphyrins.Conclusions– These observations collectively offer a novel opportunity to remedy porphyria by targeting the Wnt/beta‐catenin signaling pathway. Our next studies will further validate ALA‐D as the mechanistic target of beta‐catenin in the heme biosynthesis pathway. Because prior research has established crosstalk between autophagy and the Wnt signaling pathway, we will also investigate the role of beta‐catenin in regulating autophagy during porphyria.