BioSci 37 Midterm 2

questions we ask in clinical trials

* is the brain functioning properly?
* what do certain parts of the brain do?
* is there evidence of disease?
* how does the brain change with disease?
* does a drug improve or worsen disease?

how we can answer questions in clinical trials

* neuropsychological/cognitive testing
* PET and MRI brain imaging
* CSF and blood biomarkers
* post-mortem tissue evaluation

questions we can ask in *in vitro* studies

* how do __brain cells__ function properly?
* how do __brain cells__ change with disease?
* what happens if I alter a __brain cell__?
* how do __cells__ respond to a drug?
* is a drug toxic to __cells__?

how we can answer these questions in *in vitro* studies

* isolate brain cells (from brain biopsies or generated stem cells)
* study cell properties and functions in a dish (electrophysiology, in vitro assay, microscopy, biochemistry, genetics, etc.)

questions we can ask in *in vivo* studies

* how does the brain function properly?
* how does the brain change with disease?
* what happens to the brain if I __alter a gene, protein, or cell__?
* does a drug improve or worsen disease?

how we can answer questions in *in vivo* studies

* modify the mouse genome for human gene/mutation
* introduce human proteins/pathology
* label and track specific proteins and cells (GFP)
* study disease/insult at specific stages
* study interactions of cells and brain components together (behavior, electrophysiology, microscopy, biochemistry, genetics, etc.)

animal model

a non-human species used in biomedical research because it can mimic aspects of a biological process or disease found in humans

ways animal models aid research and human health

* to study a disease, identify the cause (virus) and test treatments
* to test the safety and efficacy of a drug treatment

examples of contributions to science due to animal models

* vaccines (such as the COVID-19 vaccines)
* insulin
* HIV treatment
* organ transplants
* tissue regeneration with stem cells
* surgical techniques

sea slug (aplysia)

* **learning and memory**
* relatively few cells in its nervous system
* brain cells are relatively large
* significant learning capabilities (gill withdrawal reflex)
* small group of neurons respond to individual behavior

fruit fly (drosophila)

* **genetics**
* simple genetics
* share 60% of the same DNA with humans
* \~75% human disease-related genes
* relatively simple to manipulate individual genes

nematode (c. elegans)

* **genetics, aging**
* simple genome (the first multicellular organism to have its genome sequenced)
* short lifespan
* simple organism and nervous system
* display signs of aging
* helped discover the utility of GFP

zebrafish (danio rerio)

* **physiology, genetics**
* extremely fertile
* ease of experimental/gene manipulation
* embryos are transparent (easy to visualize early development process)
* high degree of genetic conservation with humans
* homologous brain structures to humans (synapses)
* exhibit age-related declines in cognitive function

mice (mus musculus)

* **genetics, brain complexity**
* most commonly used animal model for studying human disease
* genetically and biologically similar to humans
* 85-99% of genome is similar to humans
* can be genetically manipulated to mimic human disease
* can be inbred to generate identical strains (accurate and reproducible experiments)
* accelerated lifespan (2-3 years; 1 mouse year = 30 human years)

using clinical studies to study Alzheimer’s disease

1. NFTs and neuropil threads (AD)
2. Neuritic plaques (AD)

using in vitro studies to study Alzheimer’s disease

skin biopsy → patient fibroblasts → patient-derived iPSCs

using in vivo studies to study Alzheimer’s disease

humans → transgenic mice → plaques + neurofibrillary tangles

transgenic

an organism or cell whose genome has been altered by the introduction of one or more foreign DNA sequences from another species by artificial means

studying learning and memory in Alzheimer’s mice

water mazes

laws and regulations for animal use in research

reduction: using the fewest number of animals

refinement: giving the animals the least amount of pain possible

replacement: developing models where animals aren’t used

several advantages that animal models offer for the study of human brain disorders

* relatively “cheap” compared to human studies
* enable drug testing
* can be made to develop human brain pathology

unique properties of stem cells

* remarkable capacity/potential to __renew__ themselves
* can __differentiate__ into many different cell types

why stem cells are important

* generate tissue during development
* maintain proper tissue __homeostasis__

pluripotent stem cells

* can differentiate into **all cells** of the adult body
* cannot give rise to an entire organism
* source: blastocyst

adult stem cells

* found in a tissue or organ and can differentiate to generate the **specialized cell** type of that tissue or organ

totipotent cells

* potential to give rise to **any type of cell** or **an entire functional organism**
* source: 4-cell embryo

multipotent cells

* can develop into more than one cell type, but are more limited than pluripotent cells
* give rise to a limited range of **cells within a tissue**
* source: organs

advantages of embryonic stem cells

* can propagate indefinitely in an undifferentiated state - potential to differentiate into any cell type of the body
* relatively easy to grow

disadvantages of embryonic stem cells

* ethical implications associated with use; collecting ESCs results in the destruction of the blastocyst
* high rate of cell division - risk of tumor formation
* risk of rejection by body
* harbors donor’s genes

therapeutic potential of embryonic stem cells

cell replacement/regenerative therapies, tissue engineering and disease modeling

advantages of adult stem cells

* with limited capacity of self-renewal, pose lesser risk of tumor formation
* less moral implications associated with use
* less risk of rejection

disadvantages of adult stem cells

* rare, present in small quantities
* relatively hard to harvest/purify
* not as plastic as ESCs (cannot differentiate into as many different cells)
* during aging, adult stem cells accumulate damage

therapeutic potential of adult stem cells

cell replacement therapies

how neural stem cells differ from other stem cells

neural stem cells are relatively quiescent and do not participate in tissue renewal or replace neurons lost to injury or disease

neural stem cells

* multipotent stem cells found in the adult brain
* can differentiate into astrocytes, oligodendrocytes, and neurons

induced pluripotent stem cells

derived from skin or blood cells that have been reprogrammed back into an embryonic-like (pluripotent) state

advantages of iPSC

* development of an unlimited source of any type of human cell needed for therapeutic purposes
* move away from controversial use of human embryonic stem cells
* potential for personalized therapy to get around risk of immune rejection

disadvantages of iPSC

* cost and time
* still need immunosuppressant for transplant
* development of teratoma (cancer risk)
* still harbor donor’s genetics and epigenetics

therapeutic potential of iPSC

* similar to other stem cells, modeling and investigating human diseases (unlimited supply of once-inaccessible human tissue), screen drugs

brain organoids

* hPSC-derived three-dimensional in vitro culture systems that recapitulate the developmental processes and organization of the developing human brain
* can be formed by iPSC

potential use of stem cells

1. replace or repair damaged tissue or group of cells that can’t heal itself
2. use stem cells to provide nutrients to sick cells
3. enhance endogenous neurogenesis

stem cells for neurodegenerative diseases

* stem cells treatment designed to target and create dopamine neurons
* clinical trials have been controversial
* patients reported dyskinesia
* __Parkinson’s disease pathology may propagate from host to grafts__

caveats of stem cells for neurodegenerative diseases

* can the brain integrate new neurons?
* tumor formation
* immune rejection
* __new transplanted cells may develop the same pathology__

alternative strategy of stem cells for neurodegenerative diseases

stem cells can be used to deliver trophic or neuroprotective factors to the brain

neurodevelopmental disorders

a group of conditions that appear during childhood involving some alteration or disruption in the development of the CNS

intellectual disability (mental retardation)

* failure to acquire intellectual abilities across cognitive domains at a normal rate (before 18 years)
* defined as an IQ of less than 70
* difficulties in adaptive functioning/life skills such as communication, self-care, home living, and social or interpersonal skills

causes of intellectual disability

genetics, infections, substances, metals/chemicals, UV radiation, lack of nutrition, oxygen deprivation, head injury

genetic causes of intellectual disability

* chromosomal abnormalities
* copy number variations (CNVs) - abnormal number of copies of one or more sections of DNA
* single gene mutations

Down syndrome

* occurs when a person has an extra (full or partial) copy of chromosome 21
* most frequent form of ID

clinical features of Down syndrome

dysmorphic features, seizures, psychomotor slowing and congenital malformation

physical features of Down syndrome

low muscle tone, small stature, upward slant to the eyes, single deep crease across center of the palm

trisomy 21 (nondisjunction)

when an error in cell division occurs, called nondisjunction, and results in an embryo with three copies of chromosomes instead of two

translocation

when the total number of chromosomes in the cells remains 46; however, an additional full or partial copy of chromosome 21 attaches to another chromosome, usually chromosome 14

mosaicism

when an individual has a mixture of two types of cells, some containing the usual 46 chromosomes and some containing 47

clinical presentation of Down syndrome

* morphosyntax, verbal short-term memory, and explicit long-term memory (impaired language and verbal memory abilities)
* seizures
* early-onset dementia that resembles Alzheimer’s disease

macroscopic features of Down syndrome

* reduced brain volume in frontal and temporal areas and cerebellum
* functional disturbances in hippocampus

microscopic features of Down syndrome

* alterations in dendritic spine structure
* decreased number/distribution of neurons
* synaptic degeneration
* reduced neurogenesis
* Alzheimer’s disease-related pathology

Down syndrome and Alzheimer’s disease

* most people with Down syndrome develop AD pathology by middle age
* early onset familial AD caused by mutations in PSEN1, PSEN2, and APP
* APP, amyloid precursor protein, is a gene that is located in chromosome 21
* rare DS translocation cases where APP is not triplicated do not develop AD

trisomy 13

Patau syndrome

trisomy 18

Edwards syndrome

a case of DS caused by chromosomal translocation may have

it may have some or all Chr21 genes triplicated

fragile x syndrome

* genetic condition that causes intellectual disability
* affect __1:2000 boys__ and 1:8000 girls
* inherited in an x-linked dominant pattern
* caused by a mutation in a single gene, located on the x chromosome
* mutation of DNA segment called __CGG triplet repeat__ within the __FMR1 gene__, creating a microscopic appearance of a gap
* CGG segment is repeated more than __200 times__
* turns off the FMR1 gene, which prevents the gene from producing __FMRP protein,__ which disrupts nervous system functions (synaptic connectivity)

clinical symptoms of fragile x

* visuospatial and verbal impairments
* behavioral characteristics may include stereotypic movements and atypical social development
* some also meet the diagnostic criteria for autism

autism spectrum disorder (ASD)

broad range of conditions characterized by challenges with social skills, repetitive behaviors, speech, and nonverbal communication

prevalence of ASD

* affects 2% of children
* increasing worldwide
* 1 in 36 children in the US
* boys are 4 times more likely than girls

autistic disorder

* impairments in areas of the brain responsible for **social interaction, communication, and imaginative play (skills and behavior)**
* apparent before age 3
* also includes stereotyped behaviors, interests, and activities

what are causes of autism?

both genetic and environmental factors

cerebrovascular demand

* CNS accounts for \~2% of total body weight
* CNS receives 15% of the blood that the heart pumps to all the body’s organs and tissue under resting conditions
* CNS has a high rate of metabolic activity; high demand for glucose and oxygen

cerebrovascular perfusion

20% of all oxygen and 50% of all glucose consumed goes to the brain

internal carotid arteries

* front
* carries blood to the brain

vertebral arteries

* back
* carries blood to the brain

arteries

deliver oxygenated blood, glucose, other nutrients to the brain

veins

carry deoxygenated blood back to heart, removing carbon dioxide, lactic acid, and other metabolic products

why the CNS is sensitive to interruptions in blood flow

1. cells of the CNS can’t store glycogen and therefore must obtain glucose directly from blood
2. most cells of the CNS don’t have access to fatty acids for energy, which increase demands for glucose
3. CNS cells can’t obtain energy from anaerobic metabolism during periods of reduced oxygen availability, thus requiring uninterrupted oxygen and glucose support to stay alive

stroke

* occurs when blood flow to the brain is blocked
* when there isn’t enough blood flow to the brain to meet metabolic demand, this limited oxygen supply leads to brain tissue damage and loss of neurological function
* aka transient ischemic attack or cerebrovascular accident

prevalence of strokes

* no. 3 cause of death in the US
* every 40 seconds someone in the US experiences one
* risk increases with age; for each decade after age 55, risk doubles

ischemic stroke

* 80-85% of all strokes
* blockage inside a blood vessel that deprives an area of the brain from glucose and oxygen
* two types of blockages: __embolic__ or __thrombotic__

hemorrhagic stroke

* 15-20% of all strokes
* weakened or diseased blood vessels rupture leading to bleeding into or around the brain
* when an artery bleeds into the brain, the brain cells and tissue do not get oxygen and nutrients
* pressure can also build up and irritation and swelling can occur, leading to further brain damage

thrombotic ischemic stroke

* caused by a thrombus (blood clot) that develops in the arteries and occludes the artery
* usually seen in older persons with high cholesterol, diabetes, and atherosclerosis
* may be preceded by one or more “mini-strokes” or transient ischemic attacks (TIAs)

transient ischemic attacks

* result from a temporary blockage of an artery
* stroke symptoms resolve in less than 24 hours
* usually resolves in 15-20 mins
* more than 1/3 of people will go on to have an actual stroke
* 5% within 1 month
* 12% within 1 year
* 20% within 2 years
* 25% within 3 years

embolic ischemic stroke

* occurs when a plaque or blood clot that forms elsewhere in the body (embolus), breaks off, travels to the brain and blocks the artery
* often result from heart disease or heart surgery
* occurs rapidly and without any warning

two main categories of hemorrhagic strokes

* intracerebral hemorrhage
* subarachnoid hemorrhage

intracerebral hemorrhage

bleeding is from the blood vessels within the brain

subarachnoid hemorrhage

bleeding is in the subarachnoid space

types of stroke

* ischemic stroke
* hemorrhagic stroke

hemorrhage (from high blood pressure)

* ruptured aneurysm
* arteriovenous malformations (AVMs)

aneurysm

a weakened, ballooned area of the artery wall

arteriovenous malformations (AVMs)

consists of a disorderly tangled web of arteries and veins

signs of a stroke

* sudden numbness or weakness, especially in one side of the body
* sudden confusion or trouble speaking or understanding speech
* sudden trouble speaking in one or both eyes
* sudden trouble walking, dizziness, or loss of balance or coordination
* sudden severe headache with no known cause

penumbra

* zone of reversible ischemia around the core of the irreversible infarction - salvageable in the first few hours after ischemic stroke onset

treatments for ischemic stroke

* tissue plasminogen activator (tPA)
* endovascular or mechanical thrombectomy
* carotid endarterectomy

tissue plasminogen activator (tPA)

* treatment for ischemic stroke
* helps dissolve clot and improve blood flow (must give within 3 hours of stroke onset)

endovascular or mechanical thrombectomy

* treatment for ischemic stroke
* clot in large artery

carotid endarterectomy

* treatment for ischemic stroke
* severe buildup of plaque

treatments for hemorrhagic stroke

surgery to clip aneurysm (stop bleeding), remove blood, reduce pressure (shunt)

traumatic brain injury

* non-degenerative, non-congenital insult to the brain from an external mechanical force
* possibility of temporary or permanent impairments of cognitive, physical, and psychosocial functions
* associated with a diminished or altered state of consciousness
* one form of acquired brain injury

the “silent epidemic”

* most individuals don’t know about brain injury, let alone its consequences or impact on behavior
* minor blows to the head or “concussions” are often not perceived as “brain injuries,” and yet 15% of these individuals will have chronic problems post injury
* most people assume one needs to lose consciousness to have a brain injury

mild TBI

* 85% of all TBIs
* seen ER or MD office
* identified as a “concussion”
* not followed by medical community in many cases

moderate to severe TBI

* 15% of all TBIs
* typically hospitalized
* identified as “TBI”
* known and followed by medical community

mild TBI/concussion

* 85% have full recovery within 3-6months post event
* 15% experience chronic symptoms which significantly interfere with their daily functioning