Mutant Protein in Muscle Linked to Neuromuscular Disorder
A new therapeutic target for Kennedy’s disease and a potential treatment
Sometimes known as Kennedy’s disease, spinal and bulbar muscular atrophy (SBMA) is a rare inherited neuromuscular disorder characterized by slowly progressive muscle weakness and atrophy. Researchers have long considered it to be essentially an affliction of primary motor neurons – the cells in the spinal cord and brainstem that control muscle movement.
But in a new study published in the April 16, 2014 online issue of Neuron, a team of scientists at the University of California, San Diego School of Medicine say novel mouse studies indicate that mutant protein levels in muscle cells, not motor neurons, are fundamentally involved in SBMA, suggesting an alternative and promising new avenue of treatment for a condition that is currently incurable.
SBMA is an X-linked recessive disease that affects only males, though females carrying the defective gene have a 50:50 chance of passing it along to a son. It belongs to a group of diseases, such as Huntington’s disease, in which a C-A-G DNA sequence is repeated too many times, resulting in a protein with too many glutamines (an amino acid), causing the diseased protein to misfold and produce harmful consequences for affected cells. Thus far, human clinical trials of treatments to protect against these repeat toxicities have failed.
In the new paper, a team led by principal investigator Albert La Spada, MD, PhD, professor of pediatrics, cellular and molecular medicine, and neurosciences, and the associate director of the Institute for Genomic Medicine at UC San Diego, propose a different therapeutic target. After creating a new mouse model of SBMA, they discovered that skeletal muscle was the site of mutant protein toxicity and that measures which mitigated the protein’s influence in muscle suppressed symptoms of SBMA in treated mice, such as weight loss and progressive weakness, and increased survival.
In a related paper, published in the April 16, 2014 online issue of Cell Reports, La Spada and colleagues describe a potential treatment for SBMA. Currently, there is none.
The scientists developed antisense oligonucleotides – sequences of synthesized genetic material – that suppressed androgen receptor (AR) gene expression in peripheral tissues, but not in the central nervous system. Mutations in the AR gene are the cause of SBMA, a discovery that La Spada made more than 20 years ago while a MD-PhD student.
La Spada said that antisense therapy helped mice modeling SBMA to recover lost muscle weight and strength and extended survival.
“The main points of these papers is that we have identified both a genetic cure and a drug cure for SBMA – at least in mice. The goal now is to further develop and refine these ideas so that we can ultimately test them in people,” La Spada said.
Pictured: striated human skeletal muscle.
Spheres of influence
Specific language impairment (SLI) is something of a misnomer. It’s a condition in which a person, typically first identified as a child, has difficulty speaking or communicating normally, but without obvious cause. Their hearing and general health are fine. There are no environmental or rearing experiences to explain it. There are no other signs of developmental delay or neurological disorder.
SLI seems hardly specific at all. And it’s the most common of childhood language disorders, affecting 7 percent of children.
“The primary requirements for the diagnosis are the failure to master spoken and written language expression and comprehension despite normal nonverbal intelligence and no sensory or other physical or medical condition that could cause it,” said Tim Brown, PhD, a developmental cognitive neuroscientist in the UC San Diego School of Medicine’s Department of Neurosciences and the UC San Diego Center for Human Development.
“Because it’s largely a diagnosis of exclusions, SLI likely has more than one cause and might be made up of different subtypes. Different kids with SLI can have very different profiles of language strengths and weaknesses.”
Although there are standard clinical treatments for speech production disorders, said Brown, there is no universally accepted treatment for SLI, in part because the problem is believed to involve non-motor “high-level” aspects of language.
In a recent paper published in the journal Frontiers in Human Neuroscience, Brown, Julia L. Evans, PhD, of the Center for Research in Language at UC San Diego and the School of Behavioral and Brain Sciences at the University of Texas, Dallas, and colleagues, describe using a technology called anatomically constrained magnetoencephalography imaging to look for “higher-level” aspects of language in a young SLI patient without requiring him to make speech movements or process auditory input.
They discovered that the adolescent boy’s brain represented objects in the opposite side of the brain than most people. “When he thinks about common objects, like a mouse, house, door, leaf or whale, and processes them vividly (like imagining their size), he uses his right brain hemisphere whereas most people rely most strongly on their left, which is thought to be the language processing hemisphere,” said Brown.
“This was true whether he was reading printed words of the objects or viewing pictures of them. With aMEG, we were able to show the specific regions of his brain that were used, with timing accurate down to the millisecond, which has not been seen before in SLI.”
Brown said the combination of spatial and temporal resolution gained using aMEG make it a promising method for better understanding what’s happening inside the brains of individual SLI patients. He said such precision may improve diagnoses and treatment.
“For example, although all children with SLI have language impairment, it may turn out that only a subset with SLI relies heavily on their right hemisphere for the cognitive processing of objects. Because of this difference in their brain’s functional organization, we might expect different cognitive or behavioral therapies to be effective for right hemisphere object processors versus left hemisphere processors. So the information about the individual child may be useful for both a better understanding of their problem and for leading them to a more appropriate treatment.”
Human neural progenitor cells isolated under selective culture conditions from the developing human brain and directed through lineage differentiation. Neural progenitor cells are stained green; differentiated astrocytes are orange. Nuclei are stained blue. Image courtesy of the National Institute of Neurological Disorders and Stroke.
Protein Switch Dictates Cellular Fate: Stem Cell or Neuron
Researchers at the University of California, San Diego School of Medicine have discovered that a well-known protein has a new function: It acts in a biological circuit to determine whether an immature neural cell remains in a stem-like state or proceeds to become a functional neuron.
The findings, published in the February 13 online issue of Cell Reports, more fully illuminate a fundamental but still poorly understood cellular act – and may have significant implications for future development of new therapies for specific neurological disorders, including autism and schizophrenia.
Postdoctoral fellow Chih-Hong Lou, working with principal investigator Miles F. Wilkinson, PhD, professor in the Department of Reproductive Medicine and a member of the UC San Diego Institute for Genomic Medicine, and other colleagues, discovered that this critical biological decision is controlled by UPF1, a protein essential for the nonsense-mediated RNA decay (NMD) pathway.
NMD was previously established to have two broad roles. First, it is a quality control mechanism used by cells to eliminate faulty messenger RNA (mRNA) – molecules that help transcribe genetic information into the construction of proteins essential to life. Second, it degrades a specific group of normal mRNAs. The latter function of NMD has been hypothesized to be physiologically important, but until now it had not been clear whether this is the case.
Wilkinson and colleagues discovered that in concert with a special class of RNAs called microRNA, UPF1 acts as a molecular switch to determine when immature (non-functional) neural cells differentiate into non-dividing (functional) neurons. Specifically, UPF1 triggers the decay of a particular mRNA that encodes for a protein in the TGF-? signaling pathway that promotes neural differentiation. By degrading that mRNA, the encoded protein fails to be produced and neural differentiation is prevented. Thus, Lou and colleagues identified for the first time a molecular circuit in which NMD acts to drive a normal biological response.
NMD also promotes the decay of mRNAs encoding proliferation inhibitors, which Wilkinson said may explain why NMD stimulates the proliferative state characteristic of stem cells.
“There are many potential clinical ramifications for these findings,” Wilkinson said. “One is that by promoting the stem-like state, NMD may be useful for reprogramming differentiated cells into stem cells more efficiently.
“Another implication follows from the finding that NMD is vital to the normal development of the brain in diverse species, including humans. Humans with deficiencies in NMD have intellectual disability and often also have schizophrenia and autism. Therapies to enhance NMD in affected individuals could be useful in restoring the correct balance of stem cells and differentiated neurons and thereby help restore normal brain function.”
To many, Down syndrome (DS) is a childhood condition. But improved health care means that individuals with DS now routinely reach age 50 or 60 years of age, sometimes beyond. However, if they live long enough, people with Down syndrome are almost certain to develop Alzheimer’s disease (AD).
Risk estimates vary, but the National Down Syndrome Society says that nearly 25 percent of individuals with DS over the age of 35 show signs of Alzheimer’s-type dementia, a percentage that dramatically increases with age. Almost all develop dementia by the age of 60.
“The more we learn about Down syndrome and Alzheimer’s disease, the more we realize these conditions – one seen at birth, the other quite late in life – are two sides of the same coin,” said William C. Mobley, MD, PhD, professor and chair of the Department of Neurosciences at UC San Diego School of Medicine. “Autopsies of DS and AD brains reveal virtually identical pathologies – the same telltale amyloid plaques and neurofibrillary tangles.”
Under the auspices of the Alzheimer’s Disease Cooperative Study (ADCS), based at the University of California, San Diego School of Medicine, a new clinical study called the Down Syndrome Biomarker Initiative (DSBI) was launched in March 2013. According to the study’s director, Michael Rafii, MD, PhD – medical director of the ADCS – its aim is to discover indicators of Alzheimer’s and study progression of the disease, with the ultimate goal of better understanding brain aging and AD in adults with Down syndrome.
The three-year pilot study has enrolled 12 participants, aged 30 to 60 years of age. Study participants will be screened for various biomarkers of AD, using tests that include three types of brain scans, retinal amyloid imaging and blood tests, among others.
“Findings to date using MRI and amyloid PET scans indicate that individuals with Down syndrome show the same brain patterns as those in the general population with the earliest stages of the memory-robbing disease, called prodromal AD,” said Rafii. He added that indications of increased brain amyloid deposition – the insoluble protein aggregates found in the brains of patients with AD that are thought to be an underlying cause of the disease – is similar in individuals with DS and those in the general population with AD.
People with amyloid deposition in the brain experience progressive cognitive deterioration. Brain atrophy – shrinking of the brain’s hippocampus – caused by the amyloid buildup, affects routine functional abilities, ultimately leading to complete physical disability.
“By understanding the progression of the disease in people with Down syndrome and those in the general population, we hope discoveries can be made in each group that can be shared between both populations,” said Rafii.
The design of the DSBI pilot study is patterned after the Alzheimer’s Disease Neuroimaging Initiative (ADNI), which began in 2004 to establish neuroimaging and biomarker measures of AD. ADNI tracked the changes taking place in the brains of 800 older people, either free of symptoms or diagnosed with late-stage mild cognitive disorder and early Alzheimer’s disease.
“Our aim is for the Down Syndrome Biomarker Initiative to mirror ADNI’s successes,” Rafii said. “ADNI has helped the international Alzheimer’s research community learn significant lessons about the pathology and biomarkers of AD, which in turn has driven new ways of looking at the disease and new studies that we hope will lead to viable treatments. We are confident we can do the same thing for Down syndrome.”
$100 Million Gift Launches Sanford Stem Cell Clinical Center
UC San Diego-based effort will speed discoveries to new drugs and treatments for patients
In a bold and singular step toward delivering the therapeutic promise of human stem cells, businessman and philanthropist T. Denny Sanford has committed $100 million to the creation of the Sanford Stem Cell Clinical Center at the University of California, San Diego.
The Sanford Center will accelerate development of drugs and cell therapies inspired by and derived from current human stem cell research; establishing, promoting and disseminating clinical trials and patient therapies that will help more quickly transform promise into reality.
“This gift and the creation of the Sanford Stem Cell Clinical Center will further UC San Diego’s leadership in stem cell science and therapeutics, and advance our region’s reputation as an international, collaborative hub for stem cell research,” said Pradeep K. Khosla, chancellor of UC San Diego. “This Center will support the goals and vision of our strategic planning process by translating discoveries into therapies that will improve and save lives.”
The Sanford Center will integrate operations at four locations: the UC San Diego Jacobs Medical Center and a nearby proposed clinical space, both scheduled to open in 2016; the UC San Diego Center for Advanced Laboratory Medicine (CALM); and the Sanford Consortium for Regenerative Medicine (SCRM). It will provide essential physical and human resources needed to leverage stem cell research currently being conducted at the Sanford Consortium – an innovative “collaboratory” of San Diego scientists from UC San Diego, the Sanford-Burnham Medical Research Institute, the Salk Institute for Biological Studies, The Scripps Research Institute and the La Jolla Institute for Allergy & Immunology – and other institutions on and around the Torrey Pines mesa, such as the J. Craig Venter Institute.
“Every day, scientists learn more about the regenerative powers of stem cells, which tantalize with their potential to treat, cure, even prevent, myriad afflictions, including cancer, Lou Gehrig’s disease and spinal cord injury. I see it in the amazing collaborative advances by researchers and doctors in the Consortium and across the La Jolla mesa,” said Sanford. “I believe we’re on the cusp of turning years of hard-earned knowledge into actual treatments for real people in need. I want this gift to push that reality faster and farther.”
The image above depicts 12 functional regions of the brain clustered by genetic influence, either in terms of cortical thickness or by cortical surface area. The numbers identify specific regions. For cortical thickness: 1. Motor-premotor-supplementary area; 2. Superior parietal cortex; 3. Inferior parietal cortex; 4. Perisylvian region; 5. Occipital cortex; 6. Ventromedial occipital cortex; 7. Ventral frontal cortex; 8. Temporal pole; 9. Medial temporal cortex; 10. Middle temporal cortex; 11. Dorsolateral prefrontal cortex and 12. Medial prefrontal cortex. For surface area: 1. Motor-premotor cortex; 2. Dorsolateral prefrontal cortex; 3. Dorsomedial frontal cortex; 4. Orbitofrontal cortex; 5. Pars opercularis and subcentral region; 6. Superior temporal cortex; 7. Posterolateral temporal cortex; 8. Anteromedial temporal cortex; 9. Inferior parietal cortex; 10. Superior parietal cortex; 11. Precuneus; and 12. Occipital cortex.
Delving deeper into brain-building
Given its incredible structural complexity – 100 billion chattering neurons connected by a network of perhaps a quadrillion synaptic connections – it can hardly be surprising that the actual construction of a human brain is equally complex and marvelous.
A new paper by researchers at UC San Diego School of Medicine and VA San Diego Healthcare System underscores that point by plotting for the first time how genes influence the development and thickness of the cerebral cortex – the thin, outermost sheet of neural tissue, often dubbed “gray matter,” that plays a key role in high-level mental functions like memory, attention, perceptual awareness, thought, language and consciousness.
Writing in this week’s early edition of PNAS, William S. Kremen, PhD, professor of psychiatry, and colleagues describe mapping genetic influences and the varying thicknesses of the cortex.
The work adds a new dimension to a 2012 study by the same scientists that rendered the first atlas of the surface of the human brain based on genetic information.
“There are two major dimensions on the cortical ribbon or cortical sheet,” said first author Chi-Hua Chen, PhD. “One is the horizontal dimension for the expansion of surface area and the other is the vertical dimension for the size of cortical thickness. The 2012 work was to study the genetic topography of surface area; this study was to study cortical thickness.”
The researchers found that genetic influences work differently depending upon the direction taken during brain development. On the surface of the cortex, the effects are most striking horizontally, with maximum differences between those at the anterior or front of the brain compared to the posterior or back of the brain. With cortical thickness, the differences were dictated vertically, with maximum deviation measured dorsal (top) to ventral (bottom).
According to Chen, the findings confirm other evidence that cortical construction involves different mechanisms of brain development. “I think the importance and relevance of this study is that human cortical morphology is under genetic control that shows orderly spatial patterns on the cortical ribbon,” she said. Previous animal studies had suggested as much, but the concept of brain development through genetic gradation has not been well-studied in humans.
While there are no immediate clinical applications for the research, Chen and Kremen say the findings will further understanding of how complex genetic influences affect cortical morphology and aid future efforts to identify involved genes and associated neurological disorders.
“The genetic underpinnings of the brain are poorly understood, especially for the human brain,” said Kremen. “New genomic technologies are making it possible to explore this area and answer, from a genetic perspective, how genes affect brain development and how they are involved in neurological disorders like Alzheimer’s disease, mild cognitive impairment, schizophrenia and autism.
A transmission electron micrograph (false color) depicting a neuron from a patient who suffered from Alzheimer’s disease. The cell nucleus is green, the body of the cell yellow and the surrounding tissue blue. Filaments that form neurofibrillary tangles – a hallmark of AD – are colored red. Image courtesy of Thomas Deerinck, NCMIR
Why don’t we all get Alzheimer’s disease?
Alzheimer’s disease afflicts an estimated 5 million Americans, with the number projected to triple by 2050. Currently, no therapy has been shown to slow the progression of the neurodegenerative disease, let alone cure it. The last drug to even temporarily ease symptoms of AD – memantine – was approved a decade ago.
These are worrisome facts that fuel profound questions and concerns, not least among them whether we can afford not to find a remedy.
But the dilemma presents an altogether different question as well: Why don’t we all get Alzheimer’s disease?
The happy reality is that the vast majority of people will never develop the devastating neurological condition. Subhojit Roy, MD, PhD, an associate professor in the departments of Pathology and Neurosciences at the UC San Diego School of Medicine, and colleagues recently proposed an answer in a paper published in the journal Neuron.
As it turns out, every brain cell possesses the ingredients necessary to spark AD, but nature has wisely devised ways to keep the explosive cellular ingredients apart.
“It’s like physically separating gunpowder and match so that the inevitable explosion is avoided,” said Roy, a cell biologist and neuropathologist in the Shiley-Marcos Alzheimer’s Disease Research Center at UC San Diego. “Knowing how the gunpowder and match are separated may give us new insights into possibly stopping the disease.”
The main players are a pair of proteins called APP and BACE-1, both abundant in the brain but largely kept apart from one another. In AD, said Roy, these proteins too often combine with calamitous consequences.
You can read the full news release and watch a video here.
The epigenetics of Parkinson’s disease
Parkinson’s disease (PD) is a neurodegenerative disorder with high incidence in the elderly, caused by a combination of environmental and genetic factors. In addition, epigenetic changes – changes in gene expression that are caused by non-genetic factors – such as DNA methylation have recently been associated with PD.
In the August 1 online edition of the Landes Biosciences journal Epigenetics, researchers from the University of California, San Diego School of Medicine investigated genome-wide methylation in brain and blood samples from PD patients. They observed a distinctive pattern of methylation involving many genes previously associated with the disease, supporting the role of epigenetic alterations as a molecular mechanism in neurodegeneration.
DNA methylation, a biochemical process that is one of the methods used to regulate the expression of genes, represents a highly promising biomarker for neurodegenerative disorders. Emerging techniques allow monitoring DNA methylation from blood – a method that could replace post-mortem brain tissue as a way to detect PD.
“Since early identification of pathological changes is crucial to enable therapeutic intervention in Parkinson’s disease before major neurologic damage occurs, these findings could prove important in monitoring disease progression and the effectiveness of treatment,” said lead author Paula Desplats, PhD, project scientist with the Department of Neurosciences at UC San Diego School of Medicine.
In this study, Desplats and UC San Diego colleagues Eliezer Masliah, MD, Wilmar Dumaop and Douglas Galasko, MD, report differential methylation for several genes, and identified concordant methylation alterations in a subset of genes in both the brain and blood samples of patients with PD.
Earlier studies by the UC San Diego researchers reported a significant decrease in DNA methylation in the frontal cortex of patients with PD and the related disorder called Dementia with Lewy bodies. Here, they further investigated the extent of epigenetic deregulation by analyzing genome-wide DNA methylation profiles in both postmortem frontal cortex samples and peripheral blood leukocytes (or PBLs) from the same individuals in a cohort of PD patients. They then compared these profiles to those of age-matched, healthy control subjects. Individual methylation profiles obtained from blood distinguished control subjects from those with PD.
“We observed similar overall methylation patterns in the brain and blood, and that the same functional groups were affected – genes involved with cell communication, as well as with cellular and metabolic processes, such as genes related to cell death,” Desplats said.
The scientists’ analyses suggest that a number of methylation changes are shared between brain and blood, positioning 124 genes (which co-varied among blood and brain tissues) as candidates for biomarker discovery.
Since accurate diagnosis of PD cannot currently be achieved until clear motor features have developed (which occurs when half of more of neurons in a particular region of the brain called the substantia nigra), increasing efforts are being dedicated to identifying early, non-motor symptoms. These may include depression and sleep disorders as well as olfactory dysfunction or reduced sense of smell.
Top: Vesicles containing APP (green) and BACE (red) are normally segregated in neurons. Bottom: After neuronal stimulation, known to produce more beta-amyloid, APP and BACE converge in common vesicles, depicted in yellow.
Why Don’t We All Get Alzheimer’s Disease?
Though one might think the brains of people who develop Alzheimer’s disease (AD) possess building blocks of the disease absent in healthy brains, for most sufferers, this is not true. Every human brain contains the ingredients necessary to spark AD, but while an estimated 5 million Americans have AD – a number projected to triple by 2050 – the vast majority of people do not and will not develop the devastating neurological condition.
For researchers like Subhojit Roy, MD, PhD, associate professor in the Departments of Pathology and Neurosciences at the University of California, San Diego School of Medicine, these facts produce a singular question: Why don’t we all get Alzheimer’s disease?
In a paper published in the August 7 issue of the journal Neuron, Roy and colleagues offer an explanation – a trick of nature that, in most people, maintains critical separation between a protein and an enzyme that, when combined, trigger the progressive cell degeneration and death characteristic of AD.
“It’s like physically separating gunpowder and match so that the inevitable explosion is avoided,” said principal investigator Roy, a cell biologist and neuropathologist in the Shiley-Marcos Alzheimer’s Disease Research Center at UC San Diego. “Knowing how the gunpowder and match are separated may give us new insights into possibly stopping the disease.”
The severity of AD is measured in the loss of functioning neurons. In pathological terms, there are two tell-tale signs of AD: clumps of a protein called beta-amyloid “plaques” that accumulate outside neurons and threads or “tangles” of another protein, called tau, found inside neurons. Most neuroscientists believe AD is caused by the accumulating assemblies of beta-amyloid protein triggering a sequence of events that leads to impaired cell function and death. This so-called “amyloid cascade hypothesis” puts beta-amyloid protein at the center of AD pathology.
Creating beta-amyloid requires the convergence of a protein called amyloid precursor protein (APP) and an enzyme that cleaves APP into smaller toxic fragments called beta-secretase or BACE.
“Both of these proteins are highly expressed in the brain,” said Roy, “and if they were allowed to combine continuously, we would all have AD.”
But that doesn’t happen. Using cultured hippocampal neurons and tissue from human and mouse brains, Roy – along with first author Utpal Das, a postdoctoral fellow in Roy’s lab, and colleagues – discovered that healthy brain cells largely segregate APP and BACE-1 into distinct compartments as soon as they are manufactured, ensuring the two proteins do not have much contact with each other.
“Nature seems to have come up with an interesting trick to separate co-conspirators,” said Roy.