Transcript lecture03-cell-physiology

Cellular Participation
In Physiology
Jim Pierce
Bi 145a
Lecture 3, 2009-2010
Cellular Physiology
 There is more to cells than just performing basal
functions.
 Cellular Physiology is the study of how cells
perform both basal and tissue specific functions.
 It is the bridge between molecular biology and
tissue function.
Cellular Physiology
 General Cellular Physiology

The study of inputs, metabolism, and outputs.

Our goal for this lecture is to look at examples of
inputs and outputs.
Cellular Physiology
 Specific Cellular Physiology

This is the study of specific aspects of cellular
function.

Our goal in this lecture is to discuss some of the
common functions: membrane function, cellular
structure, cellular motors, and secretion.
General Cell Physiology
 Homeostasis versus Active Function

Often, we want to do more than
“cruise along” at status quo.

This means doing stuff
Homeostasis
 What is homeostasis?
 It is central to understanding physiology, and makes
metabolism much easier.
 It is the property of a system to try to maintain
constancy in the face of external perturbations.
Homeostasis
 Regulation

When a system maintains some variable despite
internal or external perturbation.
 Control

When a force adjusts the output of a system over
time.
 Refrigerator Thermostat
 Glycogen in a Myocyte
Homeostasis
 Figuring out the Refrigerator is easy
 The thermostat controls

The “dial” indicates the set point
 A circuit in the Refrigerator regulates.


It compares the actual temperature to
the thermostat’s set point
It heats or cools accordingly
Refrigerator
Cooling
Homeostasis
 Glycogen is not so easy.
 What controls glycogen levels?


There is no thermostat.
The myocyte does not receive a specific
“glycogen level signal.”
Homeostasis
 What controls glycogen levels?

There are external signals that inform the myocyte of the
state of the body.

There are internal signals that inform the myocyte of the
state of the cell.

The cell must integrate these signals to make that
decision.
Homeostasis
 The way a cell integrates these signals to
make that decision is called
A Control Structure
Homeostasis
 How is glycogen level regulated?



Because there is no thermostat,
it is not a simple “compare” like the fridge
Instead the pathway “pays attention” to every
reaction, intermediate, and final product
This is called a
Regulatory Structure
Homeostasis
 How is glycogen level regulated?
 The Regulatory Structure is affected by
the Control Structure.
 It is through those interactions that
the Regulatory Structure obeys the
Control Structure
Homeostasis
 What makes up these structures?
 Cells Do Chemistry.

(they do physics, too, but I don’t like physics so I won’t
talk about it)
 Chemical Compounds (stuff)
 Processes Involving Chemical Compounds (a way
to change stuff)
Homeostasis
 Structures are composed of reactions
AB
CD
EF
Metabolism
Xsource
supply
demand
-->
M -->
(in a nutshell)
Xsink
Regulatory Network
Xsource
supply
demand
-->
M -->
(in a nutshell)
Xsink
Control Network
Xsource
supply
demand
-->
M -->
(in a nutshell)
Xsink
Why is this confusing?
 The final product has the greatest effect on
the flux through metabolism
 So the USE of the final product
exerts CONTROL
Regulation versus Control
 So certain Regulatory structures give
“Control” to the end product
 This is probably why biologists use
“regulate” and “control” interchangeably
 Just remember, like precision and accuracy,
control and regulation are different!
Metabolism and its Control
 So how do we describe these things?
 We start with a Model of the system
Metabolic Pathway
A B C D
A set of metabolites and reactions involving those metabolites.
(note that a metabolic pathway can be described by graph theory)
Generalized Linear Metabolic
Pathway
A B C D
Generalized Branched
Metabolic Pathway
Generalized Substrate Cycle
Metabolic Network
Control and Regulation
 We can then describe how any given thing
(enzyme, molecule, extrinsic parameter)
affects any other given thing
 This gives a bunch of variables
 This allows a mathematical model
Control in Dynamical Systems
Models That Exist:
 Linear Systems

Linear Models
 Non-Linear Systems


Non-Linear Models
Linear Models
Metabolism
 There is more to metabolism than just the graph of
the reactions
 Location of the reactions

Cytosolic, Membrane Bound, Nuclear
 Job in “the bigger picture”

Anabolism versus Catabolism
Control by Supply
 Feedforward Control:

1) Can achieve high control of flux

2) High control of flux forces us to have low
control of metabolites!

(That means AMPLIFICATION)
Control By Demand
 Feedback Control

1) Can achieve high control of flux

2) High control of flux forces us to have high
control of metabolites!
Metabolic Control Analysis
 We can prove that:

1) Feedback is the way we get control of both
flux and concentration.

2) Feedforward is the way we get control of flux
and amplification.
Internal State
 The first consideration in “doing stuff”
is the Internal State of the Cell
 The set of DNA, RNA, and protein (especially
“transcription factors”)
 Organelles and Compartmentalization
 Membrane and its Potential
 Secondary messengers
Internal State
 Sometimes, the decision to Activate
is the Internal State
 The best studied example is Cell Cycle


There is an internal clock
(multiple, actually)
In many cases, the ticking of the clock alone is
the largest stimulus for cell division
Internal State
 A closely related (and more interesting) example is
Early Development
 Much of the earliest patterning results from internal
state



Distribution of Bicoid mRNA (Drosophila)
Distribution of Vg-1 protein (Xenopus)
Random Genetic and Positional Noise
(Chick rotates with gravity,
Mouse random based on position in ICM)
(Bi 182 for more info!)
Internal State
 Other basal functions include:



Basal secretion in glands
Basal membrane potential patterns
Anabolism and Catabolism
for Housekeeping
Internal State
 In the case of cell cycle,
the output includes:





Replicating DNA and organelles
Nuclear Division
Cytosol Division
A huge number of checkpoints
Lots of error correcting
Internal State
 In the case of early development
the output consists of:


Spacial and Temporal Patterning
of space (intra and extracellular)
Interpreting “Internal state” into
Cellular Phenotype
General Cell Physiology
 Obviously, though, internal state cannot be
the only cue!
 In a complex organism, even making ATP
depends on the state of the organism!

(a fat cell should never steal glucose
from a starving brain cell)
General Cell Physiology
 Types of Inputs:
 Small Molecules


Neurotransmitters, Steroids, Peptides
Non steroid, non peptide hormones
General Cell Physiology
 Types of Inputs:
 Large Molecules




ICAMs, Selectins, Integrins
Lipoproteins
Other Immunoglobulins
Other Glycoproteins
Small Molecules
 Why Small Molecules?

They are very versatile

They can carry information (in both
concentration and concentration gradient)
They can diffuse or be transported.

Small Molecules
 Why Small Molecules?



They are very efficient
The earliest “computation” on small molecules
was probably bacterial chemotaxis
Food (i.e. reduced molecules) was transduced
into swimming behavior
Small Molecules
 Why Small Molecules?

They are very efficient

This system can be harnessed by using specific
small molecules as a signal

Ever notice that many neurotransmitters are
decarboxylated amino acids?
Small Molecules
 Examples of Small Molecules
 Addition / Integration


Two inhibitory cells both release GABA onto the
same dendrite, increasing hyperpolarization
Each parathyroid cell releases hormone into the
blood, and response is a function of “total
hormone” levels.
Small Molecules
 Retention

Insulin binds to its receptor and is internalized,
providing continued signaling.
 Degredation

Serum Catecholamine-O-Methyl-Transferase has
different rates of catecholamine removal than
neuronal reuptake machinery
Small Molecules
 Gradient


Retinoic Acid (vitamin A) and HOX genes
DPP in certain non-mammal animals
 Target


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Autocrine – stimulates self
Paracrine – stimulates neighbor
Neurocrine – neural synapse
Endocrine – stimulates distant cell via blood
Neuroendocrine – neural secretion into blood
Large Molecules
 Why Large Molecules?


They can “mark” an area of extracellular space.
(i.e. they stay put)
They convey information about tissue structure
(both cell-cell and cell-ECM).
Large Molecules
 Consider Neural Crest Cells
 Early development “encodes” space with a set of
small molecules, gradients, and large molecules.
 Neural crest cells migrate through this space, using
the cellular computer to respond to spacial
differences
Large Molecules
 Consider a skin injury…
 The cells at the edge of the injury lose the
suppressing signal from cell-cell adhesion
receptors.
 …But they cannot grow without the stimulating
signal from the basement membrane.
Large Molecules
 Thus, these large signals are key to tissue
functioning.
 We spend so much time thinking about the
small signals (Bi/CNS 150) that we
sometimes forget how much information is
encoded in these large molecules.
Large Molecules
 Every time two cells stick together, they are
communicating
 Every time a cell sits in the extracellular
matrix, it is listening to its surroundings
General Cell Physiology
 Also remember: a huge portion of the signals
are suppressive.
 In the brain…
 On the basement membrane…
 In the glands...
General Cell Physiology
 Secondary Messengers
 yuk.
Secondary Messengers
 Words of advice about these guys:
 Anything can function as a secondary
messenger if it can convey information, such
as small molecules, assembled structures,
and even the membrane itself.
Secondary Messengers
 Always think about the cellular compartment where
the secondary messenger is located; different
compartments have different properties.



The surface of the membrane is two dimensional, and
therefore is better for diffusion.
Cytosolic messengers can overcome three dimension
diffusion by assembly.
On the flip side, cytosolic messengers can also change
compartments and locations in the cell.
Secondary Messengers
 Do not fall into the trap of thinking of certain
messengers as “activating” or “suppressing.”



cAMP
cGMP
Ca++
Secondary Messengers
 “Secondary messengers” only get their name
because they're supposedly restricted to the
cell itself.


Some hormones (steroids) compute like
secondary messengers
Some secondary messengers (nitric oxide) can
change cells like hormones.
General Cell Physiology
 Concept Questions?
Cancer
 We talked about:



Homeostasis
Regulation versus Control
How one could actually study it
 Now:

Cancer
Cancer
 Tumor


Tumere – “swelling”
What can cause swelling?



Too Many Cells
Too Much Extracellular Matrix
Too Much Fluid
 Neoplasm


Neo – “new” Plasm – “growth”
Too Many Cells
Cancer
 Neoplasm




Benign – Cells stay where they are
Malignant – Cells invade somewhere new
Often benign ends in –oma (lipoma)
Often malignant ends in
-carcinoma = malignant from epithelium
 -sarcoma
= malignant from meso/endothelium

Cancer
 Is benign “benign?”

A benign fatty growth that squishes the trachea
and suffocates the patient
 Is malignant “malignant?”

A slow growing skin cancer that never causes
any symptoms and the patient
dies 20 years later of a heart attack
Cancer
Cancer
Multi-Hit Theory
 Cancer doesn’t develop overnight
 After “watching” many different tumors, one
begins to notice a progression.
 Over time, the tumor gets uglier, bigger,
grows faster, and grows in new places.
Multi Hit Theory
 The multi-hit theory was proposed simply by
watching the DNA
 The older or more severe the tumor…
 … the more DNA mutations that
could be found.
Multi Hit Theory
 So it was hypothesized that cancer develops
by sequential epigenetic mutations
 In that case, a predisposition to cancer occurs
from germ line mutations, which is how
many important genes were found
Multi Hit Theory
 Further Support arrived with the
identification of viruses that induce cancer
 These viruses contained mutated genes


v-myc (v-genes in general) = Viral myc
c-myc (c-genes) = Cellular myc
Multi Hit Theory
 These viral genes were called
Oncogenes – (onko (greek) – mass )
 Their corresponding cellular genes were called
“proto-oncogenes” (proto – first)
 They behave (generally) as
gain-of-function phenotype
Multi Hit Theory
 Another class of genes were described that
provided “resistance” to carcinogenesis
from viruses
 These genes were called
Tumor Suppressor Factors
 They behaved (generally) like
loss of function phenotype
Multi Hit Theory
 So the multi-hit theory is the idea that cancer
arises through a series of steps
 Each one corresponds to a “gain of function” or
“loss of function” mutation
in a specific gene
 Thus explaining what surgeons had been
observing since Brahman period medicine in early
India
Multi Hit Theory
 But that implies that cancer is
“Growth out of control”
 Uncontrolled Cell Cycle, which accelerates
and accelerates.
Cancer
 So why is it so difficult to grow
cancer cells in a dish?
Cancer
 Primary Cultures






Died if they weren’t attached to a surface
Died if there were too many
Died if there were too few
Died without serum or growth factors
Died with too much serum or growth factors
…And often just died anyway
Cancer
 HeLa cells

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1951 – Johns Hopkins Medical School
Henrietta Lacks, mother of four
Cervical Cancer cells were cultured by George
Gay, MD without permission.
They grew “horrifically”
Cancer
 Prior to HeLa cells, primary cultures
of human cells had a “finite” lifespan
 Just to keep them alive for a week took the
addition of “serum” with its panoply of
unknown factors.
Cancer
 So how could cancer be so awful,
if it won’t even grown in a dish?
 The answer lies in “phenotypes”
 Cancer is better thought of as a
“Disease of Gain-of-Phenotype”
Cancer
 There are many different phenotypes:

Needs




basement membrane
neighboring cells
growth factors
Abilities




Secretion, Absorption
Metabolism
Cell Cycle
Computation
Cancer
 These include “new” or “unusual”
phenotypes:

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
Invasion through basement membrane
Ability to migrate
Ability to live in a new milieu
Blood
 Lymph Nodes
 Other Tissues

Cancer

Evasion of Immune System


Resistance to killing (similar to viruses)
Resistance to Aging
Telomeres
 DNA Damage

Cancer

Secretion of Hormones
Autocrine Stimulation
 Growth Factors
 Recruitment of “support” (angiogenesis)

Cancer
 So every tumor is a different combination of
“phenotypes”
 Disease progression is sequential addition of
new phenotypes, each which result from
mutations
Cancer
 External / Internal signals for survival
 Gaining proliferative phenotype
 Losing apoptotic / senescent phenotype
 Gaining metastatic phenotypes
 Avoiding immune respone
 Angiogenesis and other novel phenotypes
Cancer
 These mutations often make the cell appear
less differentiated and more multipotent.
 So in many ways, understanding Cancer is
very similar to understanding Stem Cells
(and their differentiation phenotypes)
Cancer
 For more on Clinical Aspects of Cancer
Try out my brand new Bi 23, Winter 09-10
Cancer Examples
 Esophageal Adenocarcinoma

Fastest Rising Western Cancer
(~500% in the last 30 years)
Normal Esophageal Mucosa
Normal Layers
Esophageal Cancer
 Chronic gastroesophageal reflux

Leads to Acid and Bile Exposure
 The cells
will try to
protect
themselves
Barrett’s Esophagus
With Esophagitis
Esophageal Cancer
 To defend itself, the cell “gains” the
phenotype of “mucous secretion”
Normal
Barrett’s
Esophageal Cancer
 This is called “metaplasia”
- Metaplasia is when one tissue type changes to
another tissue type that “naturally” occurs in the
body in a different location
 Metaplasia requires that the cell respond to
stimuli and change phenotype
Esophageal Cancer
 The mechanisms of metaplasia depend on
the tissue and stimulus, but often involve
DNA damage
 In the case of Esophageal Cancer, bile acids
are carcinogenic



Skin Cancer – UV light
Lung Cancer – Smoking
Cervical Cancer – HPV
Esophageal Cancer
 Not surprisingly, continued acid exposure
allows progressive accumulation of DNA
damage
 It becomes carcinoma when:


It grows without regard to neighbors
It is able to cross the basement membrane
Esophageal Cancer
Barrett’s
Adenocarcinoma
Adenocarcinoma
Cancer Progression
 What we see is:


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Primary Injury (bile)
Progressive DNA damage
Gain of Phenotypes
“Pre-Cancer” – not yet across the
Basement Membrane
“Cancer” – crossed over
Metastasis – gone somewhere else
Good Cancer / Bad Cancer
 Why focus on cell cycle and apoptosis?
 Removing checkpoints and error correcting
facilitates gain-of-phenotype
 Apoptosis is the solution for excessive DNA
damage, broken apoptosis leads to proliferation
despite severe damage.
Questions?