Session 5
What drives ATP synthesis?
Chemical potential (change in pH, inside is alkaline) Electrical potential (inside is more negative) Proton-motive force
Adipogenesis the process of
preadipocytes differentiating into adipocytes
Describe the enzymatic reaction catalyzed by Sirt1
1. Catalyzed deacetylation of several proteins by consuming NAD+, generating NAM and 2'-O-acetyl-ADP-ribose 2. NAM is recycled back into NAD+ by the enzymes NAMPT (nicotinamide phosphorybosyltransferase), NMNAT, and NMN
Explain how muscle cells and brown fat cells are related
1. Derived from the same progenitor cell 2. Similar structure: Contain many mitochondria 3. Similar function: The many mitochondria in both use reduced agents from food breakdown to generate CO2 and water.
What does exercise induce?
1. Expression of peroxisome proliferation-activated receptor gamma coactivator 1 alpha. This boosts the expression of the membrane protein fibronectin type III domain containing 5 (FNDC5) 2. FNDC5 is proteolytically cleaved, and results in the release of irisin 3. Irisin is carried in the blood to white adipose tissue, which stimulates the browning of white fat
What are the molecular pathways involved in improved glucose homeostasis from calorie restriction, exercise, and resveratrol on the mitochondrial function and metabolic health
1. Robert stops eating his daily snicker 2. Less ATP produced 3. Decreased ATP levels causes AMPK to be phosphorylated (activated) by AMP and ADP binding to the gamma subunit which phosphorylates Thr 172 in the alpha subunit by kinases 4. Activated AMPK results in an increase in the NAD+ to NADH ratio (more oxidized than reduced) from catabolic pathways. AMPK also phosphorylates PGC1 alpha and primes it for deacetylation by SIRT1. 5. This ratio activates the deacetylase sirtuin 1 (SIRT1) which impacts mitochondrial capacity and allows in improved glucose homeostasis. sirtuin 1 deacetylases PGC1 alpha results in improved mitochondrial capacity and metabolic health More UCPs expressed, with UCP1 mRNA expression increased in adipocytes and UCP2 upregulated in skeletal muscle cells. Induction of genes that encode proteins of the mitochondrial respiratory chain, and total mitochondrial content is increased in these cells. In muscle cells, basal oxygen consumption is also notably increased.
How many calories does gluconeogenesis require per day
600
What is the mechanism regulating AMP-activated protein kinase (AMPK) activity
AMPK is a heterotrimeric complex of alpha, beta, and gamma subunits. AMP and ADP binding to the gamma subunit allosterically activates AMPK and facilitates the phosphorylation of Thr 172 site in the alpha subunit by upstream kinases
As ATP is used up, what happens?
ATP when used up, products are produced that are sensed by AMP-activated protein kinase, which orders cells to recharge by absorbing and burning more fat and sugar to produce ATP.
What is FOXO1 phosphorylated by and what happens to it?
Akt (kinase) phosphorylates FOXO1-> FOXO1 is excluded from the nucleus, where it is then ubiquitinated and degraded by the proteasome. This decreases gluconeogenesis in hepatocytes as glucose-6-phosphatase is no longer transcribed.
What happens in people who are nutritionally deprived
Anti-adipogenetic signals emanate from both the preadipocytes and mature adipocytes. Combined, this stops adipogenesis
UCP1 expression is increased by irisin in what cells?
Brown and beige adipose tissue, which results in less ATP produced while also being used, which results in weight loss and insulin sensitivity
What do the two types of progenitor cells in white adipose tissue yield?
Classical white fat cells that store energy in the form of fat droplets and to beige (or brite) fat cells. Beige fat cells express UCP1 and are similar in function to brown cells, but come from different progenitors.
What causes an increase in PGC1 expression in BAT and skeletal muscle?
Cold exposure
Symptoms of calorie restriction (cut 200 calories from daily caloric intake)
Decrease in body fat Increase in glucose tolerance Decrease in LDL cholesterol Increase in HDL cholesterol Decrease in triacylglycerol
Overall result of AMPK effect on liver and skeletal muscle
Decreased glucose levels Decreased ectopic fat deposition Increased insulin sensitivity Better metabolic milieu for the prevention or treatment of T2D, such as decreased circulating glucose, reduced plasma lipid, and ectopic fat accumulation as well as enhanced insulin sensitivity
AMPK effect on the liver
Decreased glucose production Decreased lipid synthesis Increased lipid oxidation
AMPK's effect on the pancreas
Decreased insulin secretion-> Decreased insulin levels
AMPK effect on adipose tissue
Decreased lipolysis Decreased lipogenesis-> Decreased circulating lipids and decrease ectopic deposition Increased insulin sensitivity
schematic representation of entry points in oxidative metabolism
Degradation of lipids, proteins, and carbohydrates gives rise to fatty acids, amino acids, and pyruvate, respectively. These molecules enter the tricarboxylic acid (TCA) cycle in the mitochondrion to be completely oxidized to CO2, with concomitant reduction of NAD+ and FAD to NADH and FADH2, respectively. The electrons are transported from the reduced coenzymes to O2 in the electron transport system, resulting in ATP synthesis.
What specifically happens in those with chronic overnutrition?
Disruption of local signaling networks, which leads to impaired adipogenesis and adipose expandability which causes two things: 1. Adipocyte hypertrophy and dysfunction, secondary adipose inflammation, and... 2. Ectopic lipid accumulation at extra-adipose sites (liver and muscle) which both contribute to insulin resistance
How does exposure to the cold affect heat production?
Exposure to the cold activates the sympathetic nervous system, which releases norepinpephrine to activate SERCA-mediated heat production under the control of SLN in cardiac and skeletal muscles. Norepinephrine also stimulates brown adipose tissue programming in conjunction with irisin and peptides released from the skeletal and cardiac muscle.
True or False: Classical white fat cells come from the same progenitor cell as a beige fat cell
False
True or False: White fat cells come from the same progenitor cell as brown fat cells
False
True or False: Brown fat cells and beige fat cells come from the same progenitor cell
False: different progenitors, different colors.
FOXO1 name
Forkhead box protein O1
What do skeletal muscle cells do with glucose 6 phosphate?
Formed from glycogen, glucose 6 phosphate enters glycolysis and serves as an energy source to support muscle contraction
What is PGC1 (peroxisome proliferator-activated receptor-gamma co-activator 1) expression high?
High levels of PGC1 mRNA expression occur in brown adipose tissue (BAT, heart, brain, and kidneys.
What happens to people who have a continuous positive energy balance (overnutrition)?
Hypertrophic adipocytes and preadipocytes secrete factors that stimulate preadipocyte differentiation. These factors block negative adipogenic signals, but release positive adipogenic factors
Symptoms of metabolic syndrome
Increase in body fat Decrease in glucose tolerance Increase in LDL Decrease in HDL Increase in triacylglycerol
Gluconeogenesis
Increased blood glucose levels from non-carbs Happens in the cytosol of liver cells FOXO1 goes to the nucleus and directs glucose metabolism toward gluconeogenesis
AMPK effect on skeletal muscle
Increased glucose uptake Increased lipid oxidation Increased mitochondrial biogenesis
UCP1 is upregulated by...
Irisin
How does irisin work?
Irisin binds to white adipose tissue and upregulates the expression of PPAR alpha and UCP1, resulting in weight loss and increased insulin sensitivity as well as the browning of white fat into beige fat cells.
How can only the liver do gluconeogenesis?
It has glucose-6-phosphatase
glucose 6 phosphatase is present in what tissues?
Liver and kidney
In its un-phosphorylated state, where is FOXO1 and what does it do?
Localized in the nucleus, it binds to the insulin response sequence located in the promoter for glucose-6-phosphatase and increases its rate of transcription, thus enhancing gluconeogenesis.
Mitochondria subunit 1 does what to NADH?
Oxidizes it to NAD+
How does PGC1 induce thermogenesis?
PGC1 coordinates transcription of genes involved in thermogenesis, such as with the induction of UCPs, genes of the mitochondrial respiratory chain such as ATP synthase and cytochrome c oxidase subunits (COX) II and IV and mitochondrial biogenesis
Explain JAK-STAT signaling in white and brown adipose tissues
Precursor cells are exposed to different transcriptional programs that control the adipogenesis of white and brown adipocytes, with JAK and STAT members being different for the two.
Why does UCP1 result in less ATP produced?
Protons are entering the channel in the intermembrane without ATP being made
In the liver, what does glycogen breakdown mean?
Release of glucose into the blood when the blood glucose levels drop, which requires glucose 6 phosphatases to convert glycogen to glucose.
What is the influence of sirtuin 1 (SIRT1) on glucose homeostasis?
SIRT1 deacetylases coactivator PGC1alpha, increasing the expression of genes for gluconeogenesis SIRT1 potentiates FOXO1 activity in hepatocytes to direct glucose metabolism towards gluconeogenesis
Explain how STAT5 is activated
STAT5 activation is carried out by kinases associated with transmembrane receptors. 1. An extracellular cytokine binds to the TM cytokine receptor. The cytokine receptor has JAK kinase bound to it. When cytokine binds to the receptor, JAK kinase is activated 2. Activated JAK adds a phosphate group to a specific tyrosine residue on the receptor, resulting in the production of phosphotyrosine 3. STAT5 binds to the phosphorylated tyrosines using the SH2 domain. 4. As JAK is still attached to the receptor, it then phosphorylates STAT5, occurring at a tyrosine residue at the c-terminus of the protein 5. Phosphorylated STAT5 dissociates from the receptor 6. The SH2 domain of the STAT 5 proteins are used to dimerize with another STAT5 protein which also uses its SH2 domain. The dimers can either be homodimers or heterodimers (STAT5-STATX). The dimerized STAT5 represents the active form of the protein, and translocates into the nucleus. Once in the nucleus, the dimers bind to STAT5 response elements, which results in the transcription of specific sets of genes.
What are the balancers between disease predisposing metabolic syndrome and calorie restriction?
Sirtuins PGC-1 AMPK Diet and physical activity
What is the role of AMPK in the regulation of whole-body glucose homeostasis?
The activation of AMPK turns on ATP-generating processes while switching off ATP-consuming processes.
What happens to the adipocytes when there is chronic overnutrition?
The fat cells (adipocytes) hypertrophy (increase in size). As a result, this causes ectopic lipid accumulation in the liver and muscle as well as adipose tissue inflammation
PPAR alpha is
a transcription factor upregulated by irisin in beige adipose tissue that results in more energy expenditure and weight loss and insulin sensitivity
Explain how muscle cells and brown fat cells differ
The mitochondria in muscle cells produce ATP in addition to CO2 and H2O to support muscle contraction, while classical brown fat cells contain mitochondria with the UCP1 protein (Uncoupling protein 1), which directly releases energy as heat and NO ATP IS GENERATED. Heat is generated instead.
Using correct JAK-STATs, explain how a precursor cell becomes a functioning white adipocyte
The precursor cell is introduced to STAT5, which induces adipogenesis and the PC becomes a white adipocyte. White adipocytes have GH receptors on them with few mitochondria in the cytoplasm. Macrophages are floating around as well. The WAs are then introduced to GH and STAT5, which results in the following functions: 1. Lipolysis 2. Insulin sensitivity 3. Lipid metabolism 4. Glucose metabolism
Using correct JAK-STATs, explain how a precursor cell becomes a functioning brown adipocyte
The precursor cell is introduced to Tyk2-STAT3, which induces adipogenesis and the PC becomes a brown adipocyte. Brown adipocytes have no receptors on them with a lot of mitochondria in the cytoplasm. Macrophages are floating around as well with IL-4 receptors. The BAs are then introduced to IL-4 and STAT6, which results in the following functions: 1. Increase energy expenditure 2. Increase in Norepinephrine
When you exercise, what do muscle cells do?
They absorb glucose and fatty acids from the bloodstream to replenish ATP, which is broken down, sensed by AMPK, and signals more absorption, which is then burnt again. Exercise accelerates this process because muscle contraction activates AMPK.
FOXO1
Transcription factor that regulates gluconeogenesis and glycogenolysis by insulin signaling
Describe the structure of mitochondrial uncoupling proteins
Tripartite structure that consists of three repeats: two hydrophobic regions per repeat that form transmembrane alpha-helices. Six alpha helical regions span the phospholipid bilayer of the mitochondrial inner membrane In each repeat, a long hydrophilic tube in the mitochondrial matrix connects the two attached transmembrane alpha helices The bundle of alpha helices can form a hydrophilic channel in the core of the UCPs, and access to this core may be controlled by gates (which are formed by the loops)
True or False: Cells that make up muscle and brown fat are derived from the same progenitor cells
True
True or False: the adipocyte number increases in childhood and adolescence, with the number leveling off and remaining constant in adulthood
True
True or False: The muscle cells do glycolysis, while the liver does gluconeogenesis
True muscle cells do not have glucose 6 phosphatase, thus they cannot perform gluconeogenesis and the resulting glucose is broken down and none is circulated through the bloodstream.
Describe the structure of ATP synthase
Two functional domains, F0 and F1 Large enzyme complex of the inner mitochondrial membrane that catalyzes the formation of ATP from ADP and Pi accompanied by the flow of protons from the p to the N side of the membrane
The lower the temperature, the greater expression of what protein in brown and beige fat cells?
UCP1
When is AMPK activated?
When you do not have enough ATP. It turns on ATP generating pathways that are catabolic. (TCA, glycolysis, fatty acid beta-oxidation, transamination deamination)
Are adipocytes fat cells?
Yes
Do hibernating animals also take advantage of UCPs, and if so, how?
Yes They use uncoupling of BAT mitochondria to generate heat during their slumber The uncoupling protein thermogenin in the mitochondria of BAT provide an alternative route for protons to re-enter the mitochondrial matrix, which causes the energy conserved by the proton pumping to be dissipated as heat
Can significant weight loss occur as a result of decrease in adipocyte volume?
Yes, this is because the adipocyte number remains the same in adults, and the reason behind weight gain and loss is not the decrease or increase in the number of adipocytes, rather their volume. Adipocytes can get bigger and smaller in size. In thin individuals, the cells shrink, which makes them look thin.
Describe glucose 6 phosphatase
integral membrane protein of the ER with its active site facing the luminal side of the ER. Hydrolyzes glucose 6 phosphates in the ER lumen after G6P is brought in via a G6P transporter protein (T1). Product glucose and Pi pass to the cytosol on specific transporters. Glucose through glucose transporter T2 and Pi through Pi transporter T3. Glucose is then transported out of the cell via GLUT2 on the PM and results in increased blood glucose concentration.
