Inclusion Body Myopathy associated with Paget's disease of the bone, and Frontotemporal Dementia (IBMPFD, OMIM 167320), was first reported by Kimonis et al. in 2000 and was subsequently attributed to being caused by mutations in the gene encoding Valosin-Containing Protein (VCP) in 2004. The disease is associated with progressive limb girdle muscle weakness and early demise from respiratory insufficiency. Muscle pathology is significant for vacuoles, TDP-43 and ubiquitin-positive inclusions. There is great interest in understanding the cellular and molecular pathophysiological mechanism(s) underlying VCP disease in view of the overlap with other common neurodegenerative diseases. Our laboratory has generated the first knock-in mouse model with the most common VCP R155H mutation, which has many features of human VCP-associated myopathy including progressive muscle, bone, spinal cord and brain pathology. The VCPR155H/R155H homozygous mice exhibit rapid progressive weakness and accelerated pathology including disrupted autophagosome formation and mitochondrial dysfunction and typically die by 21 days. However, feeding pregnant VCPR155H/+ heterozygous dams with a lipid- enriched diet (LED) resulted in the reversal of the lethal phenotype in homozygous offspring. The LED fed mice showed improvement of motor activity, muscle pathology, and autophagy/mitophagy signaling cascades. A targeted lipidomic analysis of skeletal muscle and liver revealed elevations in tissue levels of non-esterified palmitic acid and ceramide (d18:1/16:0), the latter of which has been implicated in binding and recruiting LC3-II labeled autophagosomes to damaged mitochondria for lysosomal degradation, also termed 'lethal mitophagy'. Preliminary in vitro studies demonstrated that ceramide treatments increased expression levels of the autophagy markers p62/SQSTM1 and LC3-II in myoblasts. We hypothesize that decreasing the levels of the ceramide intermediates in the homozygote mice fed the LED ameliorates the pathophysiologic manifestations of VCP disease.
In Aim 1, we will utilize the VCP mouse model and in vitro cell systems as an innovative translational approach to explore the intermediate steps in ceramide metabolism that are altered in VCP disease.
In Aim 2, we will investigate mechanisms underlying LED supplementation rescue of the sphingolipid- induced lethal autophagy, mitophagy, mitochondrial dysfunction and apoptosis signaling pathways.
In Aim 3, we will evaluate the effects of reducing ceramide on disease pathology by pharmacologic drugs. We hope that these studies will lead to potential new therapeutic strategies in VCP and related diseases.
We have discovered elevated C18 ceramides in VCP inclusion body myopathy and have rescued lethality in homozygote mice with a lipid-enriched diet. Manipulating C18 ceramide and its interaction with autophagy/ mitophagy/apoptosis signaling pathways may have therapeutic potential for VCP and related disorders.