Aberrant upregulation of the glycolytic enzyme PFKFB3 in CLN7 neuronal ceroid lipofuscinosis

Abstract

CLN7 neuronal ceroid lipofuscinosis is an inherited lysosomal storage neurodegenerative disease highly prevalent in children. CLN7/MFSD8 gene encodes a lysosomal membrane glycoprotein, but the biochemical processes affected by CLN7-loss of function are unexplored thus preventing development of potential treatments. Here, we found, in the Cln7∆ex2 mouse model of CLN7 disease, that failure in autophagy causes accumulation of structurally and bioenergetically impaired neuronal mitochondria. In vivo genetic approach reveals elevated mitochondrial reactive oxygen species (mROS) in Cln7∆ex2 neurons that mediates glycolytic enzyme PFKFB3 activation and contributes to CLN7 pathogenesis. Mechanistically, mROS sustains a signaling cascade leading to protein stabilization of PFKFB3, normally unstable in healthy neurons. Administration of the highly selective PFKFB3 inhibitor AZ67 in Cln7∆ex2 mouse brain in vivo and in CLN7 patients-derived cells rectifies key disease hallmarks. Thus, aberrant upregulation of the glycolytic enzyme PFKFB3 in neurons may contribute to CLN7 pathogenesis and targeting PFKFB3 could alleviate this and other lysosomal storage diseases.

CLN7 mutation causes aberrant redistribution of protein isoforms and contributes to Batten disease pathobiology

“…CLN7 and age-matched control iPSc were specified to iNPC capable of generating post-mitotic neurons. CLN7 neurons presented with enlarged lysosomes, and we have previously reported elevated SCMAS and disease-specific phenotypes in these CLN7 iNPC (16,17). Using a commercially available polyclonal antibody raised against the N-terminal 37 amino acids of CLN7/MFSD8, we detected characteristic immunostaining of cytosolic vesicles with partial overlap with LAMP1 and p62 immunoreactivity and intense staining of the nucleus.…”

“…We recently described a metabolic phenotype in Cln7 Δex2 mice caused by mitochondrial dysfunction resulting in elevated ROS, bioenergetic collapse ( 17 ). In alignment with this study, BD iNPC had elevated mitochondrial membrane potential and superoxide production compared to control iNPC under steady-state conditions ( Fig.…”

“…We have previously reported that CLN7 iNPC and Cln7 Δex2 mouse cortical neurons share a mitochondrial bioenergetic phenotype ( 17 ) so we sought to delineate what disease phenotypes in iNPC are due to loss-of-function in order to identify potential novel gain-of-function phenotypes. First, we confirmed that CLN7 iNPC have elevated mitochondrial membrane potential and ROS, consistent with mitochondrial stress.…”

“…Interestingly, like CLN7, CLN3 can also be considered a member of the MFS family ( 6 ). Improved understanding of molecular pathogenicity has enabled the identification of tamoxifen ( 16 ) and the PFKFB3 inhibitor AZ67 ( 17 ) as FDA approved repurposed drugs capable of ameliorating aspects of CLN7 BD in patient iNPCs and Cln7 Δex2 mice. Overall, a complete understanding from gene expression to protein functions will facilitate targeted and efficient therapies for the NCLs.…”

Long-term progression of retinal degeneration in a preclinical model of CLN7 Batten disease as a baseline for testing clinical therapeutics

“…One surprising outcome of our study was the sensitivity to intraperitoneally (IP) injected anaesthetics. Cerebral and retinal impaired lysosomal function has been shown in Cln7 KO mice, 30 , 31 , 44 , 45 , 46 which can impact the ability to metabolize drug compounds. We find that care should be taken in treatment of human CLN7 Batten disease patients when prescribing drugs or considering anaesthetic options and routes of delivery.…”