What Are Memories Made Of?

Summary: A new study evaluates the roles AKT proteins play in synaptic plasticity, brain development and neuropsychiatric disorders.

Source: University of Colorado at Boulder.

Ask a nonscientist what memories are made of and you’ll likely conjure images of childhood birthday parties or wedding days. Charles Hoeffer thinks about proteins.

For five years, the assistant professor of integrative physiology at CU Boulder has been working to better understand a protein called AKT, which is ubiquitous in brain tissue and instrumental in enabling the brain to adapt to new experiences and lay down new memories.

Until now, scientists have known very little about what it does in the brain.

But in a new paper funded by the National Institutes of Health, Hoeffer and his co-authors spell it out for the first time, showing that AKT comes in three distinct varieties residing in different kinds of brain cells and affecting brain health in very distinct ways.

The discovery could lead to new, more targeted treatments for everything from glioblastoma–the brain cancer Sen. John McCain has–to Alzheimer’s disease and schizophrenia.

“AKT is a central protein that has been implicated in a bevy of neurological diseases yet we know amazingly little about it,” Hoeffer said. “Our paper is the first to comprehensively examine what its different forms are doing in the brain and where.”

Discovered in the 1970s and known best as an “oncogene” (one that, when mutated, can promote cancer), AKT has more recently been identified as a key player in promoting “synaptic plasticity,” the brain’s ability to strengthen cellular connections in response to experience.

“Let’s say you see a great white shark and you are scared and your brain wants to form a memory of what’s going on. You have to make new proteins to encode that memory,” he said. AKT is one of the first proteins to come online, a central switch that turns on the memory factory.

But not all AKTs are created equal.

For the study, Hoeffer’s team silenced the three different isoforms, or varieties, of AKT in mice and observed their brain activity.

They made a number of key discoveries:

AKT2 is found exclusively in astroglia, the supportive, star-shaped cells in the brain and spinal cord that are often impacted in brain cancer and brain injury.

“That is a really important finding,” said co-author Josien Levenga, who worked on the project as a postdoctoral researcher at CU Boulder. “If you could develop a drug that targeted only AKT2 without impacting other forms, it might be more effective in treating certain issues with fewer side-effects.”

The researchers also found that AKT1 is ubiquitous in neurons and appears to be the most important form in promoting the strengthening of synapses in response to experience, aka memory formation. (This finding is in line with previous research showing that mutations in AKT1 boost risk of schizophrenia and other brain disorders associated with a flaw in the way a patient perceives or remembers experiences.)

AKT3 appears to play a key role in brain growth, with mice whose AKT3 gene is silenced showing smaller brain size.

Immunohistology using isoform-specific antibodies revealed distinct expression patterns for each AKT isoform in the hippocampus. AKT1 was mainly expressed in the cell body layers, with the greatest levels in stratum pyramidale of CA1. AKT2 was mostly expressed in specific cells in the molecular layer of the dentate gyrus, CA3 and CA1. AKT3 was also mainly expressed in the cell body layers of the hippocampus and showed strong expression in the hilus and CA3. Bottom panels show single Akt knockout (KO) tissue to validate the specificity of the antibodies. NeuroscienceNews.com image is credited to Hoeffer et al./eLife.

“Before this, there was an assumption that they all did basically the same thing in the same cells in the same way. Now we know better,” Hoeffer said.

He notes that pan-AKT inhibitors have already been developed for cancer treatment, but he envisions a day when drugs could be developed to target more specific versions of the protein (AKT1 enhancers for Alzheimer’s and schizophrenia, AKT2 inhibitors for cancer), leaving the others forms untouched, preventing side-effects.

More animal research is underway to determine what happens to behavior when different forms of the protein go awry.

“Isoform specific treatments hold great promise for the design of targeted therapies to treat neurological diseases with much greater efficacy and accuracy than those utilizing a one-size-fits-all approach,” the authors conclude. “This study is an important step in that direction.”

About this neuroscience research article

Lead author and postdoctoral researcher Josien Levenga, and postdoctoral researcher Helen Wong and graduate student Ryan Milstead also contributed to the study.

Funding: Funding provided by Alzheimer’s Association, Brain and Behavior Research Foundation, National Institutes of Health, Linda Crnic Institute, Simons Foundation, Sie Foundation.

Source: Lisa Ann Marshall – University of Colorado at Boulder
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is credited to Hoeffer et al./eLife.
Original Research: Open access research in eLife.

Cite This NeuroscienceNews.com Article

[cbtabs][cbtab title=”MLA”]University of Colorado at Boulder “What Are Memories Made Of?.” NeuroscienceNews. NeuroscienceNews, 26 January 2018.
<https://neurosciencenews.com/memory-akt-genetics-8380/>.[/cbtab][cbtab title=”APA”]University of Colorado at Boulder (2018, January 26). What Are Memories Made Of?. NeuroscienceNews. Retrieved January 26, 2018 from https://neurosciencenews.com/memory-akt-genetics-8380/[/cbtab][cbtab title=”Chicago”]University of Colorado at Boulder “What Are Memories Made Of?.” https://neurosciencenews.com/memory-akt-genetics-8380/ (accessed January 26, 2018).[/cbtab][/cbtabs]


AKT isoforms have distinct hippocampal expression and roles in synaptic plasticity

AKT is a kinase regulating numerous cellular processes in the brain, and mutations in AKT are known to affect brain function. AKT is indirectly implicated in synaptic plasticity, but its direct role has not been studied. Moreover, three highly related AKT isoforms are expressed in the brain, but their individual roles are poorly understood. We find in Mus musculus, each AKT isoform has a unique expression pattern in the hippocampus, with AKT1 and AKT3 primarily in neurons but displaying local differences, while AKT2 is in astrocytes. We also find isoform-specific roles for AKT in multiple paradigms of hippocampal synaptic plasticity in area CA1. AKT1, but not AKT2 or AKT3, is required for L-LTP through regulating activity-induced protein synthesis. Interestingly, AKT activity inhibits mGluR-LTD, with overlapping functions for AKT1 and AKT3. In summary, our studies identify distinct expression patterns and roles in synaptic plasticity for AKT isoforms in the hippocampus.

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