In a mouse model of INCL reduced S‐palmitoylation of cytosolic thioesterase APT1 contributes to microglia proliferation and neuroinflammation

Abstract

S-palmitoylation is a reversible posttranslational modification in which a 16-carbon saturated fatty acid (generally palmitate) is attached to specific cysteine residues in polypeptides via thioester linkage. Dynamic S-palmitoylation (palmitoylation-depalmitoylation), like phosphorylation-dephosphorylation, regulates the function of numerous proteins, especially in the brain. While a family of 23 palmitoyl-acyl transferases (PATS), commonly known as ZDHHCs, catalyze S-palmitoylation of proteins, the thioesterases, localized either in the cytoplasm (eg, APT1) or in the lysosome (eg, PPT1) mediate depalmitoylation. Previously, we reported that APT1 requires dynamic Spalmitoylation for shuttling between the cytosol and the plasma membrane. APT1 depalmitoylated H-Ras to regulate its signaling pathway that stimulates cell proliferation. Although we demonstrated that APT1 catalyzed its own depalmitoylation, the ZDHHC(s) that S-palmitoylated APT1 had remained unidentified. We report here that ZDHHC5 and ZDHHC23 catalyze APT1 Spalmitoylation. Intriguingly, lysosomal Ppt1-deficiency in Cln1 −/− mouse, a reliable animal model of INCL, markedly reduced ZDHHC5 and ZDHHC23 levels. Remarkably, in the brain of these mice decreased ZDHHC5 and ZDHHC23 levels suppressed membrane-bound APT1, thereby, increasing plasma membrane-localized H-Ras, which activated its signaling pathway stimulating microglia proliferation. Increased inflammatory cytokines produced by microglia together with increased complement C1q level contributed to the transformation of astrocytes to neurotoxic A1 phenotype. Importantly, neuroinflammation was ameliorated by treatment of Cln1 −/− mice with a PPT1-mimetic small molecule, N-tert(Butyl)hydroxylamine (NtBuHA). Our results revealed a novel pathway to neuropathology in an INCL mouse model and uncovered a previously unrecognized mechanism of the neuroprotective actions of NtBuHA and its potential as a drug target.

Glial Dysfunction and Its Contribution to the Pathogenesis of the Neuronal Ceroid Lipofuscinoses

“…Astrocytes resembling “A1” or neurotoxic status have been reported in more common neurodegenerative diseases such as Alzheimer's disease (AD) ( 70 ), amyotrophic lateral sclerosis (ALS) ( 71 ), and Parkinson's disease ( 72 ). Similarly, the pronounced typical A1-specific molecular signature has been recently reported in the forebrains of Ppt 1 −/− mice ( 73 ), suggesting a neurotoxic function of astrocytes in CLN1 disease. However, caution is needed in using the current A1/A2 classifications to interpret pathological roles of astrocytes, because such a binary A1/A2 paradigm may be an oversimplification of potentially more wide-ranging and heterogeneous states of astrogliosis ( 74 ).…”

Cortical interneuron loss and seizure generation as novel clinically relevant disease phenotypes in Cln2R207X mice

“…Here, we found a delay of several months between the early onset of CD68-positive microglial activation and the late onset of elevated staining for MHC-II (M1 marker) and Clec7a (M2 or DAM) in Cln2 R207X brains, suggesting progressive differences in the nature of microglial activation during CLN2 pathogenesis. In addition, our RT-qPCR evidence for changes in the expression of only a subset of A1/A2-specific astrocytic markers are in stark contrast to the pronounced typical A1-specific molecular signature transformation that occurs in Cln1 -/- mice [47]. While the contribution of the heterogeneous subtypes of reactive astrocytes to neurodegeneration remains unclear, such data highlight the distinct molecular and functional nature of astrogliosis in CLN2 disease compared with CLN1 disease.…”

IL-1R/C3aR signaling regulates synaptic pruning in the prefrontal cortex of depression

“…In addition to phosphorylation-dephosphorylation, palmitoylation-depalmitoylation, another reversible posttranslational modification, also regulates the function of numerous proteins in the brain [30]. DHHC7, a Fig.…”

“…DHHC7 is commonly suggested to be crucial for non-genomic rapid responses to steroid hormones to brain organization [32]. Besides, palmitoylation is involved in microglia proliferation and neuroinflammation [33]. A recent study showed that a palmitoylation cycle modulated the activation and nucleus translocation of STAT3 in response to inflammation [20].…”