His team searches beyond the hallmark Alzheimer’s disease proteins for alternative treatments

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In his laboratory at the USF Health Byrd Alzheimer’s Center, neuroscientist David Kang, PhD, focuses on how different types of proteins damage the brain when they accumulate there. In the case of Alzheimer’s disease, decades of good science has zeroed in on amyloid and tau, as the two types of hallmark proteins driving the disease process that ultimately kills brain cells.

Dr. Kang and his team investigate molecular pathways leading to the formation large, sticky amyloid plaques between brain cells, and to the tau neurofibrillary tangles inside brain cells –including the interplay between the two proteins. But, he is quick to point out that amyloid and tau are “not the full story” in the quest to understand how normally aging brains go bad.

“Our goal is to understand as much of the entire Alzheimer’s disease process as possible and then target specific molecules that are either overactive or underactive, which is part of the drug discovery program we’re working on,” said Dr. Kang, professor of molecular medicine and director of basic research for the Byrd Alzheimer’s Center, which anchors the USF Health Neuroscience Institute.

Neuroscientist David Kang, PhD, (third from left)  stands with his team in his laboratory at the Byrd Alzheimer’s Center, which anchors the USF Health Neuroscience Institute.

Attacking dementia from different angles 

Dr. Kang’s group takes a multifaceted approach to studying the biological brain changes that impair thinking and memory in people with Alzheimer’s, the most common type of dementia, as well as Lewy body, vascular and frontotemporal dementias.

That includes examining how damaged mitochondria, the energy-producing power plants of the cell, contribute to pathology in all neurodegenerative diseases. “Sick mitochondria leak a lot of toxins that do widespread damage to neurons and other cells,” Dr. Kang said.

Dr. Kang’s team was the first to identify how mutations of a gene, called CHCHD10, which contributes to both frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), cause both mitochondrial dysfunction and protein pathology called TDP-43. Their findings on the newly identified mitochondrial link to both neurodegenerative diseases were published in Nature Communications in 2017.

The role of selective degradation in ridding cells of abnormal proteins, old or damaged organelles (including mitochondria) and other debris is another key line of research pursued by Dr. Kang and colleagues.

A single stained nerve cell | Microscopic image courtesy of Kang lab

“We believe something more fundamental is going wrong in the brain during the aging process to tip the balance toward Alzheimer’s disease – beyond what we call proteinopathy” or deposits of malformed proteins like toxic amyloid and tau, said Dr. Kang, whose work is bolstered by nearly $8 million in grant funding from the National Institutes of Health (NIH), the Veterans Administration (VA merit awards) and the Florida Department of Health.

“I think one of the fundamental things happening is that the (cellular) plumbing system isn’t working to clear out all the accumulating junk,” he said. “That’s why we’re looking at the protective clearance mechanisms (autophagy and mitophagy) that would normally quickly remove misfolded proteins and dysfunctional mitochondria.”

Unfortunately, pharmaceutical trials to date have yielded no effective treatments for Alzheimer’s disease, the sixth leading cause of death in the U.S.  Most clinical studies have centered on developing medications to block or destroy the amyloid protein plaque formation, and a few have targeted the tau-containing neurofibrillary tangles. The five Alzheimer’s drugs currently available may provide temporary relief of symptoms, such as memory loss and confusion. But, they do not prevent or delay the mind-robbing disease as toxic proteins continue to build up and dismantle the brain’s communication network.

Lesson learned: The critical importance of intervening earlier

Some scientists argue that the “amyloid hypothesis” approach is not working. Dr. Kang is among those who maintain that amyloid plays a key role in initiating the disease process that leads to brain atrophy in Alzheimer’s – but that amyloid accumulation happens very early, as much as 10 to 20 years before people experience memory problems or other signs of dementia.

Early detection and treatment are key, Dr. Kang says, because as protein plaques and other lesions continue to accumulate in the brain, reversing the damage may not be possible.

“One reason we’ve been disappointed in the clinical trials is because so far they have primarily targeted patients who are already symptomatic,” Dr. Kang said. “Over the last decade we’ve learned that by the time someone is diagnosed with early Alzheimer’s disease, or even mild cognitive impairment, the brain has degenerated a lot. And once those nerve cells are gone they do not, for the most part, regenerate… The amyloid cascade has run its course.”

As protein plaques and other lesions continue to accumulate, becoming apparent with MRI imaging, reversing the damage may not be possible.  So, for anti-amyloid therapies – or even those targeting downstream tau – to work, patients at risk of Alzheimer’s need to be identified and treated very early, Dr. Kang said.

USF Health is recruiting healthy older adults with no signs of memory problems for a few prevention trials. A pair of Generation Program studies will test the effectiveness of investigational anti-Alzheimer’s drugs on those at high genetic risk for the disease before symptoms start. And, the NIH-sponsored Preventing Alzheimer’s with Cognitive Training (PACT) study is examining whether a specific type of computerized brain training can reduce the risk of mild cognitive impairment and dementias like Alzheimer’s disease in those age 65 and older.

To accelerate early intervention initiatives, more definitive tests are needed to pinpoint biomarkers that will predict Alzheimer’s disease development in genetically susceptible people. Dr. Kang is hopeful about the prospects.  His own team investigates how exosomes, in particular the lipid vesicles that shuttle proteins and other molecules from the brain into the circulating bloodstream, might be isolated and used to detect people at risk of proteinopathy.

“I think within the next five years, some type of diagnostic blood test will be available that can accurately identify people with early Alzheimer’s brain pathology, but not yet experiencing symptoms,” he said.

Graduate research assistant Yan Yan, a member of Dr. Kang’s research team, works at a cell culture hood.

Searching for alternative treatment targets

Meanwhile, Dr. Kang’s laboratory continues searching for other treatment targets in addition to amyloid and tau — including the enzyme SSH1, which regulates the internal infrastructure of nerve cells, called the actin cytoskeleton. SSHI, also known as slingshot, is needed for amyloid activation of cofilin, a protein identified by the USF Health neuroscientists in a recent study published in Communications Biology as a possible early culprit in the tauopathy process.

“Cofilin is overactive in the brains of Alzheimer’s patients so if we can inhibit cofilin by targeting slingshot, it may lead to a promising treatment,” Dr. Kang said.

Ultimately, as with other complex chronic diseases, Alzheimer’s may not be eliminated by a single silver-bullet cure.  Rather, Dr. Kang said, a combination of approaches will likely be needed to successfully combat the neurodegenerative disorder, which afflicts 5.8 million Americans.

“I think prevention through healthy living is definitely key, because brain aging is modifiable based on things like your diet as well as physical activity and brain exercises,” he said.  “Also, we need to focus on earlier diagnosis, before people become symptomatic, and develop next-generation drugs that can attack the disease on multiple fronts.”

Xingyu Zhao, PhD, a research associate in the Department of Molecular Medicine, is among the scientists in Dr. Kang’s laboratory studying the basic biology of the aging brain.

Fascinated by how the brain works — and malfunctions

Dr. Kang came to USF Health in 2012 after nearly 20 years as a brain researcher at the University of California San Diego, where he earned M.S. and PhD degrees in neurosciences and completed NIH National Research Service Award fellowships in the neuroplasticity of aging.

As an undergraduate Dr. Kang switched from studying engineering to a dual major in science/psychology. He began focusing on neurosciences in graduate school, he said, because tackling how the brain works and malfunctions was fascinating and always challenged him.

“With every small step forward, we learn something else about the basic biology of the aging brain,” said Dr. Kang, “It’s not just helpful in discovering what therapeutic approaches may work best against Alzheimer’s disease – we’re also learning more about other neurodegenerative conditions affecting the brain.”

In addition to leading day-to-day research operations at the Byrd Center and helping to recruit new Alzheimer’s investigators, Dr. Kang holds the Mary and Louis Fleming Endowed Chair in Alzheimer’s Research and serves as a research neurobiologist at the James A. Haley Veterans Haley Veterans’ Hospital.

He has authored more than 50 peer-reviewed journal articles on brain aging and Alzheimer’s disease research. A member of the NIH Clinical Neuroscience and Neurodegeneration Study Section since 2016, he has served on multiple national and international editorial boards, scientific panels and advisory boards.

Dr. Kang sits next to a computer monitor depicting stained microscopic images — a single neuron (far left) and the two hallmark pathological proteins for Alzheimer’s disease, tau tangles (center) and amyloid plaques (right).

Some things you may not know about Dr. Kang

• His parents were Presbyterian missionaries in Africa, so he spent nine years of his early life (third through 10^th grade) in Nigeria.
• Dr. Kang practices intermittent fasting, often forgoing breakfast and eating only within an 8-hour window. Animal studies indicate the practice may contribute to lifespan and brain health by improving cellular repair through the process of autophagy, he said. “Autophagy really kicks your cells’ plumbing system into gear to clear out all the waste.”

-Video and photos by Allison Long, USF Health Communications and Marketing

An antagonist that blocks a specific interaction between the protein apoE and amyloid precursor protein appears promising in a preclinical study led by USF Health

TAMPA, Fla. (June 12, 2019) — Apolipoproten E (apoeE) is a major genetic risk factor for the development of Alzheimer’s disease, yet the protein tends to be understudied as a potential druggable target for the mind-robbing neurodegenerative disease.

Study lead author Darrell Sawmiller, PhD (left), and senior author Jun Tan, PhD, MD

Now a research team led by the University of South Florida Health (USF Health) Morsani College of Medicine reports that a novel apoE antagonist blocks apoE interaction with N-terminal amyloid precursor protein (APP). Moreover, this peptide antagonist, known as 6KApoEp, was shown to reduce Alzheimer’s-associated beta amyloid (β-amyloid) accumulation and tau pathologies in the brain, as well as improving learning and memory in mice genetically engineered to mimic symptoms of Alzheimer’s disease.

Many failed anti-amyloid therapies for Alzheimer’s disease have been directed against various forms of the protein β-amyloid, which ultimately forms clumps of sticky plaques in the brain. The presence of these amyloid plaques is one of the major hallmarks of Alzheimer’s disease.

The USF Health research findings suggests that disrupting apoE physical interaction with N-terminal APP may be a new disease-modifying therapeutic strategy for this most common type of dementia.

The preclinical study was published online May 2 in Biological Psychiatry, a journal of Psychiatric Neuroscience and Therapeutics.

Microscopic image shows the merging of APP (red) and apoE (green) in brain cells.  This co-localization (yellow) suggests an age-associated increase in apoE-N-terminal APP interaction and higher production of the toxic amyloid-β (Aβ) protein characteristic of Alzheimer’s disease.

“For the first time, we have direct evidence that the N-terminal section of apoE itself acts as an essential molecule (ligand) to promote the binding of apoeE to the N-terminal region of APP outside the nerve cell,” said the study’s lead author Darrell Sawmiller, PhD, an assistant professor in the USF Health Department of Psychiatry & Behavioral Neurosciences. “This receptor-mediated mechanism plays a role in the development of Alzheimer’s disease. Overstimulation of APP by apoE may be an earlier, upstream event that signals other neurodegenerative processes contributing to the amyloid cascade.”

“Initially we wanted to better understand how apoE pathologically interacts with APP, which leads to the formation of β-amyloid plaques and neuronal loss,” said study senior author Jun Tan, PhD, MD, a professor in the USF Health Department of Psychiatry & Behavioral Neurosciences.  “Our work further discovered an apoE derivative that can modulate structural and functional neuropathology in Alzheimer’s disease mouse models.”

Microscopic image depicts the merging of APP and apoE in cell cultures (above).  Depleting the N-terminal region of apoE reduces APP and apoE physical interaction (below).

Alzheimer’s disease is a global epidemic, afflicting an estimated 50 million people worldwide and 5.8 million in the U.S, according to the Alzheimer’s Association.  With the aging of the Baby Boomer generation, the prevalence of the debilitating disease is expected to increase dramatically in the coming years.  Currently, no treatments exist to prevent, reverse or halt the progression of Alzheimer’s disease, and current medications may only relieve dementia symptoms for a short time.

Dr. Sawmiller, Ahsan Habib, PhD, and Lucy (Hauyan) Hou, MD, of the USF Health Department of Psychiatry and Behavioral Neurosciences (all lead authors) collaborated with colleagues from the Laboratory of Neurosciences at the National Institute on Aging (NIA), the Department of Neuroscience at Johns Hopkins University School of Medicine, the USF Center for Neurosurgery and Brain Repair, and Saitama Medical University in Japan.  Other study authors included Takashi Mori, PhD; Anran Fan, PhD; Jun Tian, BS; Brian Giunta, MD, PhD; Paul R. Sanberg, PhD; and Mark P. Mattson, PhD.

The research was supported by an NIA grant from the National Institutes of Health.

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-Photos by Torie M. Doll, USF Health Communications and Marketing
-Microscopic images courtesy of Drs. Darrell Sawmiller and Jun Tan

USF Health study links Aβ-activated enzyme cofilin with the toxic tau tangles in major neurodegenerative disorders like Alzheimer’s disease

Neurofibrillary tau tangles (stained red) are one of the two major brain lesions of Alzheimer’s disease. Blue fluorescent stain (DAPI) depicts the nerve cell nuclei.

TAMPA, Fla. — The two primary hallmarks of Alzheimer’s disease are clumps of sticky amyloid-beta (Aβ) protein fragments known as amyloid plaques and neurofibrillary tangles of a protein called tau.  Abnormal accumulations of both proteins are needed to drive the death of brain cells, or neurons. But scientists still have a lot to learn about how amyloid impacts tau to promote widespread neurotoxicity, which destroys cognitive abilities like thinking, remembering and reasoning in patients with Alzheimer’s.

While investigating the molecular relationship between amyloid and tau, University of South Florida neuroscientists discovered that the Aβ-activated enzyme cofilin plays an essential intermediary role in worsening tau pathology.

Their latest preclinical study was reported March 22, 2019 in Communications Biology.

The research introduces a new twist on the traditional view that adding phosphates to tau (known as phosphorylation) is the most important early event in tau’s detachment from brain cell-supporting microtubules and its subsequent build-up into neurofibrillary tangles. These toxic tau tangles disrupt brain cells’ ability to communicate, eventually killing them.

David Kang, PhD, director of basic research at the Byrd Alzheimer’s Center, USF Health Neuroscience Institute, was senior author of the Communications Biology paper.

“We identified for the first time that cofilin binds to microtubules at the expense of tau – essentially kicking tau off the microtubules and interfering with tau-induced microtubule assembly. And that promotes tauopathy, the aggregation of tau seen in neurofibrillary tangles,” said senior author David Kang, PhD, a professor of molecular medicine at the USF Health Morsani College of Medicine and director of basic research at Byrd Alzheimer’s Center, USF Health Neuroscience Institute.

Dr. Kang also holds the Fleming Endowed Chair in Alzheimer’s Research at USF Health and is a biological scientist at James A. Haley Veterans’ Administration Hospital. Alexa Woo, PhD, assistant professor of molecular pharmacology and physiology and member of the Byrd Alzheimer’s Center, was the study’s lead author.

The study builds upon previous work at USF Health showing that Aβ activates cofilin through a protein known as Slingshot, or SSH1. Since both cofilin and tau appear to be required for Aβ neurotoxicity, in this paper the researchers probed the potential link between tau and cofilin.

The microtubules that provide structural support inside neurons were at the core of their series of experiments.

Alexa Woo, PhD, an assistant professor of molecular pharmacology and physiology at the USF Health Morsani College of Medicine, was the paper’s lead author.

Without microtubules, axons and dendrites could not assemble and maintain the elaborate, rapidly changing shapes needed for neural network communication, or signaling. Microtubules also function as highly active railways, transporting proteins, energy-producing mitochondria, organelles and other materials from the body of the brain cell to distant parts connecting it to other cells. Tau molecules are like the railroad track ties that stabilize and hold train rails (microtubules) in place.

Using a mouse model for early-stage tauopathy, Dr. Kang and his colleagues showed that Aβ-activated cofilin promotes tauopathy by displacing the tau molecules directly binding to microtubules, destabilizes microtubule dynamics, and disrupts synaptic function (neuron signaling) — all key factors in Alzheimer’s disease progression. Unactivated cofilin did not.

The researchers also demonstrated that genetically reducing cofilin helped prevent the tau aggregation leading to Alzheimer’s-like brain damage in mice.

An amyloid plaque (stained red), one of the two major brain lesions of Alzheimer’s disease, is shown here with the Aβ-activated enzyme cofilin (green) and nerve cell nuclei (blue).

“Our data suggests that cofilin kicks tau off the microtubules, a process that possibly begins even before tau phosphorylation,” Dr. Kang said. “That’s a bit of a reconfiguration of the canonical model of how the pathway leading to tauopathy works.”

Since cofilin activation is largely regulated by SSH1, an enzyme also activated by Aβ, the researchers propose that inhibiting SSH1 represents a new target for treating Alzheimer’s disease or other tauopathies. Dr. Kang’s laboratory is working with James Leahy, PhD, a USF professor of chemistry, and Yu Chen, PhD, a USF Health professor of molecular medicine, on refining several SSH1 inhibitors that show preclinical promise as drug candidates.

The research described in this Communications Biology paper was supported by grants from the VA, the NIH National Institute on Aging, and the Florida Department of Health.

Schematic of activated cofilin in tauopathy, which leads to pathological brain changes in people with Alzheimer’s disease and other major neurodegenerative disorders | Courtesy of Alexa Woo

-Photos by Allison Long, USF Health Communications and Marketing

Amyvid is the first and only FDA-approved diagnostic PET tracer for imaging beta amyloid plaques in the living brain

Tampa, FL – (Sept. 5, 2012) The USF Health Byrd Alzheimer’s Institute’s Eric Pfeiffer Imaging Center is one of only a limited number of PET imaging sites in Florida to offer Amyvid brain imaging.  Amyvid is a diagnostic PET (positron emission tomography) tracer to detect the presence or absence in the brain of significant amyloid plaques, a hallmark of Alzheimer’s disease, while patients are still alive.  The radiotracer allows physicians to see evidence of amyloid plaques in patients with cognitive impairment when providing clinical evaluation for Alzheimer’s disease and other causes of cognitive decline.

Alzheimer’s disease (AD) is one of many possible causes of dementia or cognitive impairment. Patients with symptoms of cognitive impairment can be misdiagnosed with Alzheimer’s disease, and up to one in five patients without AD pathology upon autopsy are clinically diagnosed with the neurodegenerative disease. In conjunction with clinical assessment, an imaging test or brain scan could detect the presence of neuritic, beta-amyloid plaques in the living brain.

An Amyvid PET scan is intended for use in adult patients with early stage dementia or memory problems. Amyvid is injected into the blood stream, where it binds to amyloid plaques in the living brain. An Amyvid PET scan is not a covered service under Medicare. For questions on payment and scheduling for Amyvid PET imaging, call (813) 396-0728.

 For more information about Amyvid, visit www.amyvid.com

 -USF Health-

USF Health’s mission is to envision and implement the future of health. It is the partnership of the USF Health Morsani College of Medicine, the College of Nursing, the College of Public Health, the College of Pharmacy, the School of Biomedical Sciences and the School of Physical Therapy and Rehabilitation Sciences; and the USF Physician’s Group. The University of South Florida is a global research university ranked 50^th in the nation by the National Science Foundation for both federal and total research expenditures among all U.S. universities.

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