A lay summary written by Amisha Parmar, Research Technician, The University of Sheffield.
Background
Alzheimer’s disease (AD) is a devastating neurodegenerative condition in the elderly and the most common form of dementia. This neurodegenerative condition is caused by the progressive loss of structure and function of nerve cells (neurons), that may ultimately lead to neuronal death. AD is characterised by the accumulation of insoluble, sticky protein products known as amyloid beta plaques (containing the protein amyloid beta) and neurofibrillary tangles (containing the protein TAU) in the brain. AD patients suffer with a gradual decline in memory, thinking and reasoning skills. Therapeutic interventions are ongoing, targeting the removal of the accumulated insoluble protein/s, but this approach alone may not be sufficient to reverse functional deficits in the AD brain.
Advanced therapy medicinal products (ATMPs) are medicines for humans that are based on genes (which are the coding sequence for proteins), tissues or cells. They offer revolutionary new opportunities for the treatment of disease and injury. Therefore, gene therapies that target neuroprotection (stops neurons from dying) may be an effective option to treat individuals suffering from AD. Gene therapy is a technique that modifies a person’s genes to treat or cure disease. Gene therapies involve various approaches such as replacing a disease-causing gene with a healthy copy of the gene; inactivating a disease-causing gene that is not functioning properly; or introducing a new or modified gene into the body to help treat a disease.
Both animal studies and human studies have shown that there is less of the protein Caveolin-1 (Cav-1) in diseased neurons in AD. Cav-1 plays a critical role in neuroprotection and thus, preserves higher cognitive functions such as learning and memory in the brain.
Why is the study important?
In this study, Cav-1 was chosen as a gene therapy candidate. Tests were performed to see whether Cav-1 gene therapy in an experimental mouse model of AD (PSAPP1) could improve higher brain function. PSAPP mice exhibit learning and memory deficits at 9 and 11 months, respectively, which is associated with decreased expression of Cav-1. Thus, this study provides vital information about how beneficial Cav-1 gene therapy can be in an AD mouse model and suggestive of further assessment in other neurodegenerative diseases.
What did the authors do and how did they do it?
The authors categorised PSAPP mice in two groups. One group of animals were treated with Cav-1 gene therapy. Animals in another group were not treated with anything, used as control group. The authors looked at the behaviour2 of the mice and the internal structure (morphology) of the neurons at the age of 9 months and 11 months. PSAPP mice that had been treated with Cav-1 gene therapy were compared with the control mice.
In this study, the behavioural tests named as open field and fear conditioning were used to understand the behaviour of each mouse. In the open field test, the exploratory and locomotor (movement in a transparent apparatus) activity of mice is recorded. The apparatus consists of an arena surrounded by high walls, to prevent escape, and the floor of the open field is divided into squares. The mouse is placed in the apparatus and the number of square crossings, rearing, and time spent moving are used to assess the activity of the rodent. Higher exploration and locomotion activity suggests normal behaviour of mice.
Moreover, the fear conditioning test is used to study fear learning and memory in mice. Fear Conditioning is a type of associative learning task in which mice learn to associate a particular neutral conditional stimulus (a tone) with an aversive unconditional stimulus (a mild electrical foot shock) and show a conditional response (such as freezing). After repeated pairings of tone and electrical foot shock, mouse learns to fear both the tone and training context.
What are the results?
PSAPP mice treated with Cav-1 gene therapy had elevated levels of the Cav-1 gene. Furthermore, the open field and conditional fear learning tests show that the mice which were not treated with Cav-1 gene delivery exhibited reduced learning and memory recall. In contrast diseased mice with elevated levels of the Cav-1 gene kept their memory recall function at the age of 11 months.
Furthermore, the morphology of the neurons was studied using microscopy. Various markers (proteins responsible for the maintenance of morphology in healthy neurons) were used to study the morphological changes in neurons. The localization and levels of markers of interest were assessed using advanced molecular biology techniques.
In summary, this study demonstrates that Cav-1 gene delivery delays neurodegeneration and cognitive deficits in PSAPP mouse model of AD.
What do the finding mean going forward for people with the disease?
Findings from this study suggest that Cav-1 might serve as a novel gene therapy target to preserve or delay neurodegenerative conditions in AD and other forms of brain disease of unknown causative factor/s.
Author list: Shanshan Wang, Joseph S. Leem, Sonia Podvin, Vivian Hook, Natalia Kleschevnikov, Paul Savchenko, Mehul Dhanani, Kimberly Zhou, Isabella C. Kelly, Tong Zhang, Atsushi Miyanohara, Phuong Nguyen, Alexander Kleschevnikov, Steve L. Wagner, John Q. Trojanowski, David M. Roth, Hemal H. Patel, Piyush M. Patel, and Brian P. Head
Publication details including date of publication: Mol Ther Methods Clin Dev. 2021 Mar 29; 21:434-450. doi: 10.1016/j.omtm.2021.03.021. eCollection 2021 Jun 11. PMID: 33981778
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PSAPP: Mouse carrying mutated forms of APP and PSEN1(PS) gene. In humans, alteration in these genes causes AD.
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Behavioural tests are used to study behavioural aspects of animals such as movement, learning, memory, anxiety etc.