Metabolism
Which mouse would have higher body fat? Conventionally raised mice or germ free mice. Why?
Conventionally raised mice would have higher body fat then germ free mice and conventionally raised rederived mice. This wasn't because of food intake or energy expenditure.
This is because germ free mice can't degrade plant polysaccharides. Bacteria have a great capacity to degrade plant polysaccharides (germ free mice don't have bacteria). This is because bacteria suppress transcription of fasting-induced adipose factor (Faif) from the intestine. In germ free mice, there is high expression of faif. In conventionally raised mice there is low expression. If you KO this gene, you get a lean animal (?).
What is fasting-induced adipose factor do?
It is important for regulation of the deposition of fat
Obese animals have different bacterial composition in their gut than lean animals. Describe the differences.
Obese animals have increased firmicutes and decreased bacteroidetes. OB/OB mice fed a regular mouse diet gained a lot of fat because they had different composition of microbiota.
What happens if you transfer microbiota from a donor obese mouse to a regular mouse?
This transfers the obesity phenotype of the obese mouse to a a regular mouse and it increases it's body fat
What happens if you feed a germ free mouse a high fat, high sugar diet? What would happen to a regular mouse? Why?
Germ free mice are protected from developing obesity even with a bad diet. Regular mice gained a lot of weight.
This is because germ free mice have high Faif compared to regular mice, even on the same diet. Also, there is continual activation of energy sensor (AMPK) in the liver, gut, muscle, adipose tissue in the germ free mice, which signals for them not to eat. In regular animals they have lower AMPK, so it suggests to keep eating.
What does the microbiota of obese humans look like?
It has a lack of diversity and lack of changes in the composition, similar to mice
What happens when you transfer human fecal matter to a germ free mouse?
The germ free mouse would have the characteristics of the human donor (lean or obese)
What happens if you co-house a lean mouse with a mouse that had a donation of obese microbiota (but still lean) and fed them a regular diet?
The obese mouse would stay lean because the microbiota that are responsible for normal metabolism dominated.
What happens if you co-house a lean mouse with a mouse with obese microbiota and fed them a high fat high sugar diet?
The mouse with obese microbiota would become obese.
Human microbiota can be transfered to mice, but diet, microbiota, and genetics all interact.
What happens if you take microbiota from a stunted, underweight person and give it to a mouse? What happens when you co-house it with a healthy mouse?
The microbiota wll make the mouse lean. If you co-house it with a healthy mouse, the mouse would become healthy again because healthy microbiota dominates over stunted growth microbiota. There are five bacteria that are capable of treating underweight people and bring back body weight (in mice)
Change in microbiota is linked to ___ even in the face of leanness. Explain.
A high fat diet is an independent mechanism for changing the composition of the gut microbiota and is associated with obesity, but obesity is not essential for it. Aka. High fat diet can determine microbiota, independently of obesity.
Compare the gut microbiota between wild type and ob/ob pair fed mouse (who are not obese).
Wild type mice still had distinct microbiota compared to ob/ob mice, even when they weren't obese. Ob/ob mice that are pair fed to wild type mice aren't obese because they are fed a good diet.
Ob/ob mice have a ____ (lower or higher) proportion of Akkermansia.
Lower
They fed mice a prebiotic, even with a HF diet you have a lower content of akkermansia but you can rescue that by feeding it a probiotic.
Feed ob/ob regular diet, it has low bacteria, feed it a probiotic you can stimulate the production of akkermansia.
Even when you're feeding a high fat high sugar diet, if you increased the amount of akkermansia, you can lower the fat, they become thinner even when having a bad diet.
How does Akkermansia work?
It works through actions on the enteroendocrine system by increasing the production of GLP-1 (natural ozempic) which increases insulin sensitivity and reduces inflammation.
What is bacterial LPS?
Baterial LPS is an increase in endotoxin, which you see in obese animals and humans. This is due to a change in barrier function.
LPS isn't a single molecule, it's dozens of different molecules. Not all LPS' are bad, only acylated LPS is bad
In obesity, what happens if there is a break in the barrier? What regulates this barrier?
You will get low grade inflammation and metabolic endotoxemia (leaky gut). LPS and AEA (natural endocannabinoid) regulates the barrier
How does LPS work?
LPS acts via TLR4 to give rise to changes throughout the body, but importantly, through reduction of activation of c fibres and impaired vagus satiety signaling. Vagus nerve plays a critical role in signaling that you are full. LPS messes that up by changing leptin resistance, CCK signaling, and other factors in the signaling of the gut to the brain.
Gut microbiota driven inflammation alters gut-brain axis pathways to modulate food intake.
Metabolic endotoxemia is mediated by ____
The type of LPS. Specifically acylated LPS
Bacterial LPS signals through ___ and ___
TLR4 and CD14. The primary signaling pathway makes use of MyD88
What happens if you knockout CD14 in a mouse and feed them a high fat diet?
There will be a slight reduction in body weight, but not a lot. There will be reduced adipose tissue and reduced peripheral inflammation. KO of CD14 does reduce some effects of 'leaky gut.'
What happens if you knockout TLR4 in mice?
You get an increase in body weight, but are partially protected from (reduction in) insulin resistance and inflammation.
What happens if you knockout MyD88 in intestinal epithelial cells?
There will be a small decrease in high fat diet obesity compared to a wild type on a high fat diet.
What happens if you knockout MyD88 from immune system?
There is no impact on body weight.
What happens if you knockout MyD88 in the brain?
On a normal diet, there is no difference. On a high fat diet, there is reduced body weight and fat. Not due to change in food intake, but a change in metabolism.
What happens if you knockout MyD88 in astrocytes only?
There will be a decrease in weight on a high fat diet.
What happens if you knockout TLR5?
Mice will eat 10% more than wild type mice, even on a regular diet.
If you do a fecal transplant from TLR5 KO mice and put it into a germ free mouse, they germ free mouse would eat like a TLR5 KO mouse.
This means TLR5 can regulate metabolism and behaviour effects of food intake via the brain
Where are the molecules of microbiota acting?
They work on enteroendocrine cells and regulate the release of gut hormones.
The gut microbiome regulates homeostasis via ____
peripheral serotonin.
Serotonin regulation at the level of the gut is regulated by indigenous spore forming bacteria with increases levels
What happens if you knockout the rate limiting enzyme for serotonin (TPH1)?
It will cause the animals to be lean and have reduced peripheral inflammation/metabolic dysfunction. Therefore, serotonin is also important in obesity.
What happens if you block TPH1? What happens if you give antibiotics (w/o blocking TPH1)? What happens if you give antibiotics and block TPH1?
1. Decrease in serotonin, which = decrease in blood glucose
2. Decrease in blood glucose because there is no microbiota = no signals happening (serotonin not being created)
3. Decrease in body weight and blood glucose, but no changes from the addition of TPH1 KO, which means the addition of TPH1 was linked the the gut microbiota.
Gut microbiota regulates glucose homeostasis through peripheral serotonin and levels of peripheral serotonin are dictated by the gut microbiome.
Regulation of food in take by enteroendocrine cells is through ___
The vagus nerve
What is CCK?
A gut hormone that regulates satiety.
If you give an animal CCK and a regular diet, they will stop eating
What happens if you give an animal chronic LPS exposure?
LPS blunts the normal satiety response to CCK, animals won't stop eating.
What are CART and MHC for? How do they react with LPS exposure?
CART (anorexigenic): stops you from eating (you have high levels of this when you are fed)
High levels are blunted in LPS, so you keep eating.
MCH (orexigenic): Low when you are fed, higher levels when you are given LPS, stimulating food intake.
What happens when you give an animal prebiotic fibre on a high-fat diet?
Giving animals a high level of prebiotic can reduce their food intake and alters gut bacteria (increasing bacteroidetes)
Prebiotics can regulate gut bacteria and can stimulate CCK production
How do we know the vagus is critical for food intake?
A prebiotic treated animal with it's vagus nerve ablated, no longer has suppression of food intake that is associated with fibre, proving the vagus nerve is critically important in food intake regulated by CCK in response to the changing gut bacteria
The gut microbiota regulates energy metabolism and homeostasis via ____
Gut hormones
Explain the role of dopamine in food preference.
Food that is rich in fat and sugar can stimulate dopamine neurons to induce release of dopamine in corticolimbic structures of the brain. Obesity, often associated with longterm over eating, is associated with a reduction in dopamine and dopamine receptors. Reduced dopamine functioning pathway (hypo) is suggested to be important for feeding the cycle of food intake. Obese people may not distinguish between high and low fat food, they lose the rewarding effect of food so they want more food to get the bigger reward
Explain how gut microbes participate in food preference alterations during obesity.
An experiment used lean and fat mice as donors and they did a fecal microbial transplant.
Lean normal mice that were given the fecal transplant from the fat donors showed the same degree of reduced food preference as the onese animals had. They were not excited by high fat diets because their dopamine system is down regulated.
Lean mice FMT to lean mice = the mice were happy and the high fat diet was a treat. They had regular dopamine signaling