Researchers at Università Cattolica and Fondazione Policlinico Universitario A. Gemelli IRCCS demonstrated that cognitive decline and brain damage typical of Alzheimer’s disease can be counteracted in mouse models using a nasal spray-delivered drug to inhibit overexpression of the brain enzyme S-acyltransferase (zDHHC) and reduce protein S-palmitoylation.
The studies, headed by Claudio Grassi, MD, PhD, director of the neuroscience department, and Salvatore Fusco, MD, PhD, with the collaboration of the University of Catania, were reported in PNAS “Inhibition of zDHHC7-driven protein S-palmitoylation prevents cognitive deficits in an experimental model of Alzheimer’s disease.” In their paper, the team concluded that their findings, involving post mortem brain tissue form AD patients, and in mouse models, “reveal a critical role of aberrant protein S-palmitoylation in the onset and progression of AD and provide evidence for developing therapeutic approaches targeting zDHHC enzymes.”
The development of Alzheimer’s disease is driven by alterations in certain proteins, including beta-amyloid and tau, which aggregate and accumulate in the brain. The functions of these proteins are regulated by multiple signals and modifications, including the attachment of a fatty acid molecule in a biochemical reaction called S-palmitoylation, which is performed by S-acyltransferase enzymes (zDHHC). “Protein post-translational modifications (PTM) play a crucial role in the modulation of synaptic function and their alterations are involved in the onset and progression of neurodegenerative disorders,” the authors wrote. S-palmitoylation is a PTM catalyzed by zinc finger DHHC domain containing (zDHHC) acyltransferases that affects both localization and activity of proteins regulating synaptic plasticity and amyloid-β (Aβ) metabolism.”
An increasing number of studies has shown the role of palmitoylated proteins in the regulation of synaptic plasticity and neuronal functions, the team further noted. “It has also been reported that proteins critically involved in AD (e.g., the amyloid precursor protein, amyloid precursor protein (APP), and Beta-Secretase 1, BACE1) are targets of S-palmitoylation).” However, they pointed out, the role of zDHHC enzymes and protein S-palmitoylation in the onset and progression of neurodegeneration and cognitive deficits in AD isn’t understood. “We hypothesized that aberrant S-palmitoylation of proteins regulating synaptic plasticity and Aβ metabolism might play a critical role in the development of AD.”
Through their newly reported studies the researchers observed that the post-mortem brains of Alzheimer’s disease patients, and those of mouse models of AD contained an excess of S-acyltransferase. They also found that higher concentrations of the enzyme were associated with worse cognitive performance. “… we reported that 3x Tg-AD mice, a well-characterized experimental model of AD, show increased expression of zDHHC enzymes and elevated levels of S-palmitoylation of proteins regulating synaptic plasticity and Aβ metabolism at an early phase of disease,” they stated.
“In previous studies, we demonstrated that altered S-palmitoylation of synaptic proteins plays a critical role in cognitive decline induced by metabolic diseases like type 2 diabetes (Spinelli et al., Nature Communications) and that brain insulin resistance may impact the amount of active zDHHC enzymes in the brain,” Prof. Fusco explained, citing previous work.
The authors also noted a well-established link between insulin resistance and neurodegenerative diseases, so much so that Alzheimer’s is often called type III diabetes. “The molecular crosstalk between alteration of insulin signaling and neurodegeneration has been extensively investigated, so that Alzheimer’s disease (AD) has also been named type III diabetes,” the investigators added.
“In this new study, we showed that in the early stages of Alzheimer, molecular changes resembling a scenario of brain insulin resistance cause an increase of zDHHC7 enzyme levels and alter the S-palmitoylation of key proteins involved in cognitive functions and beta-amyloid accumulation.”
“Our findings show that in animal models of Alzheimer’s disease, both pharmacological and genetic inhibition of protein S-palmitoylation can counteract the accumulation of harmful proteins in neurons and delay the onset and progression of cognitive decline,” the lead author of the study Francesca Natale, PhD, added. Post-mortem brain samples from Alzheimer’s disease patients also demonstrated elevated levels of zDHHC7 and S-palmitoylated proteins, with an inverse correlation between BACE1 S-palmitoylation levels and cognitive maintenance scores on the Mini Mental State Examination.
In experiments performed on the genetically modified AD model mice, researchers turned off zDHHC enzymes using an experimental nasal-spray containing the palmitoylation inhibitor 2-bromopalmitate. This approach successfully stopped neurodegeneration, reduced symptoms, and even extended the animals’ lifespan. “Chronic intranasal administration of the S-palmitoylation inhibitor 2-bromopalmitate counteracted synaptic plasticity and cognitive deficits, reduced the Aβ deposition in the hippocampus and extended the lifespan of both male and female 3x Tg-AD mice,” they wrote.
The investigators suggest their findings add new insight to the collective understanding of AD pathophysiology, and identify potential therapeutic targets. The collective data from the reported studies, the team concluded, “… reveal a key role of zDHHC enzymes in the development of neurodegeneration and cognitive deficits, and suggest that counteracting aberrant protein S-palmitoylation can be an additional therapeutic strategy for AD … our results may pave the way for future clinical trials, representing a significant step forward in the field of AD research and to discover effective treatments for neurodegenerative disorders.”
Grassi added, “Currently, no drugs can selectively block zDHHC7, and 2-bromopalmitate is not sufficiently precise.” However, with continued funding through the Italian Ministry of Health’s PNRR program new approaches will be tested, which may be translatable for therapeutic use. These may include genetic patches—small oligonucleotides that bind to the zDHHC7 enzyme’s RNA and prevent its maturation—or engineered proteins that can interfere with zDHHC enzyme activity.
