How is the Expansion and Shrinking of Fat Cells Controlled in Our Body?

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00:00:13.13 What is the one superpower that you would like to acquire?
00:00:17.04 If you ask me, I’d like to acquire
00:00:19.09 the superpower of Wolverine.
00:00:22.12 Not the superpower of adamantium claws,
00:00:24.25 but the superpower of regeneration:
00:00:27.19 the ability to heal a wound without leaving a scar.
00:00:31.21 Now, we often get wounded by small cuts, accidents, or surgeries.
00:00:37.13 And we almost have that superpower of healing these wounds.
00:00:42.22 But we sometimes do leave scars,
00:00:45.06 and scarring is a huge cosmetic issue.
00:00:48.29 But how do we form these scars?
00:00:51.17 Once we get wounded,
00:00:53.05 there are specialized cells known as fibroblasts.
00:00:57.05 These fibroblasts are there to produce connective tissue.
00:01:02.04 Once wounded, these fibroblasts become activated
00:01:05.26 and start producing a lot of connective tissue.
00:01:08.23 You can think of connective tissue as cement between the bricks.
00:01:13.15 This connective tissue is good for healing,
00:01:16.27 but if the activated fibroblasts continue to produce this connective tissue,
00:01:20.12 it leaves a scar.
00:01:22.11 Now, there’s a similar human condition known as scleroderma.
00:01:25.23 It’s an autoimmune disease,
00:01:28.02 in which there are a lot of activated fibroblasts
00:01:30.18 continuing to produce connective tissue,
00:01:32.24 leading to tissue stiffness.
00:01:34.28 Currently, there is no treatment available for scarring or scleroderma.
00:01:39.11 Recent research suggests that the fat layer in both these conditions
00:01:43.29 is decreased.
00:01:45.28 The fat cells in the skin lose their fat, shrink,
00:01:49.20 and convert into activated fibroblasts,
00:01:51.23 which then produce a lot of connective tissue,
00:01:54.12 leading to scarring and scleroderma.
00:01:56.25 I am interested to understand,
00:01:59.04 can we do something to prevent the loss of skin fat?
00:02:03.08 Hence, can we prevent activated fibroblasts,
00:02:05.26 and can we prevent scarring and scleroderma?
00:02:09.04 But where does the skin fat reside?
00:02:12.01 So, our skin is a protective barrier from the environment
00:02:15.28 and can be divided into two layers:
00:02:17.16 the epidermis, which is the top layer,
00:02:20.28 is packed with cells to form that barrier;
00:02:25.02 below the epidermis resides the dermis,
00:02:27.26 which is filled with connective tissue
00:02:30.01 and connective tissue-producing cells, fibroblasts.
00:02:32.29 The lower part of the dermis contains the skin fat,
00:02:35.24 or the skin fat layer.
00:02:38.28 As you can see, in both epidermis as well as dermis,
00:02:43.13 there are a lot of different types of immune cells.
00:02:46.05 They are there to fight off the pathogens
00:02:48.17 that might invade our skin.
00:02:51.00 As I will show you in this presentation,
00:02:52.24 these immune cells might play
00:02:56.16 a non-immune function in controlling the skin fat.
00:02:59.23 While I was thinking about these questions,
00:03:01.18 I was also working on different projects in the lab
00:03:05.02 to find the most interesting project
00:03:07.17 that I can take for my thesis.
00:03:10.02 At this time, the director of our institute,
00:03:13.06 professor Apurva Sarin,
00:03:15.02 found out that they have a mouse model…
00:03:17.23 when it is young and newborn,
00:03:20.05 there is no skin problem.
00:03:22.12 The skin looks completely normal.
00:03:24.11 But as it becomes an adult, the skin looks abnormal.
00:03:28.12 It loses hair, looks scaly,
00:03:30.18 and looks inflamed.
00:03:32.26 So, professor Apurva Sarin wanted to know
00:03:35.23 what is happening in the skin of these mice,
00:03:38.12 so she contacted Dr. Colin Jamora, my thesis advisor,
00:03:41.28 who has two decades of experience in skin research.
00:03:45.27 And these mice had a problem in one of the immune cells
00:03:49.04 known as regulatory T cells, or Tregs.
00:03:52.01 So, what do these Tregs normally do?
00:03:54.09 So, the function of these Tregs
00:03:56.08 is to control and keep other immune cells in our body in check,
00:04:00.16 so you can think of it as a parliament and the army.
00:04:04.15 So, the job of the parliament is to keep the army in check.
00:04:08.17 So, in the case of this mouse model,
00:04:11.05 there was a mutation specifically in the regulatory T cells,
00:04:14.26 which compromised their function,
00:04:17.11 and they were no longer able to control the immune cells.
00:04:20.22 What can happen if the parliament is dissolved or corrupted?
00:04:24.02 The army can take over.
00:04:26.16 They can build up and can lead to dictatorship,
00:04:29.19 which can be detrimental for a country.
00:04:31.26 Similarly, if the Tregs are compromised in their function,
00:04:35.13 the immune cells will start to build up —
00:04:37.13 they will proliferate and activate.
00:04:39.13 And this can be detrimental for various tissues in the body,
00:04:42.21 including skin.
00:04:45.01 For the sake of simplicity in this presentation,
00:04:47.01 I’ll be calling this mouse an inflamed mouse.
00:04:50.23 So, what is happening in the skin of this inflamed mouse?
00:04:53.21 To know this, I took a piece of skin from this inflamed mouse,
00:04:58.11 embedded it, and sectioned it.
00:05:00.29 I looked at the sections under the microscope,
00:05:04.14 and I found that the skin section was as thin as a paper.
00:05:09.13 One of the first observations that I made
00:05:12.12 was that there is no fat in the skin.
00:05:14.27 As I saw this, I rushed to Colin’s office
00:05:16.27 and told him that there’s no fat in the skin.
00:05:20.19 But there was a history.
00:05:22.05 In another experiment, I told Colin
00:05:24.18 that there’s a game changing and surprising observation,
00:05:29.02 which later turned out to be wrong.
00:05:31.02 So now, keeping this history in mind,
00:05:32.25 Colin responded to my no-fat observation as,
00:05:39.02 “fool me once, shame on you; fool me twice, shame on me,”
00:05:41.14 which means that he did not believe in my observation.
00:05:44.21 Now, to prove that my observation was correct,
00:05:47.07 I took the skin section from these mice
00:05:49.25 and performed an Oil Red O staining.
00:05:52.18 So, the Oil Red O binds to the lipids inside the fat cells,
00:05:56.26 making the fat cells red in color.
00:05:59.05 So, I first performed the Oil Red O
00:06:01.29 on the wild type skin section.
00:06:03.14 As you can see, in the wild type in the lower dermis,
00:06:06.07 you can see the red staining of Oil Red O,
00:06:08.19 suggesting that the fat layer is there.
00:06:11.25 But when I looked at the skin of an inflamed mouse,
00:06:14.16 there was no Oil Red O staining.
00:06:17.07 That means there was no fat.
00:06:19.22 This was very exciting.
00:06:21.19 This was exciting because the immune cells
00:06:24.13 are there in skin to fight off the pathogens,
00:06:26.14 to form that barrier.
00:06:28.22 But this observation suggests that there is
00:06:31.06 a non-immune function of immune cells.
00:06:34.29 And at this point, I was sure that this was going to be my thesis project.
00:06:39.00 Now, interestingly, in conditions of skin scleroderma and scarring,
00:06:44.05 the immune cell numbers are up.
00:06:47.02 Now, keeping these two observations in mind
00:06:48.28 — one, that the fat layer is decreased,
00:06:51.14 second, the immune cells are increased —
00:06:54.05 we thought, can we transfer just the immune cells
00:06:57.27 from the inflamed mouse into an immunocompromised mouse?
00:07:01.10 Can that lead to loss of skin fat?
00:07:04.06 We decided to perform this experiment.
00:07:07.04 When we transferred the immune cells
00:07:10.11 from a wild type mouse into the immunocompromised mouse,
00:07:12.19 we found that the skin fat was normal.
00:07:14.25 It was completely intact.
00:07:17.12 But when we transferred the immune cells
00:07:20.06 from the inflamed mouse into the immunocompromised mouse,
00:07:24.19 we saw a decrease in the skin fat layer.
00:07:27.11 The skin fat looked sparse.
00:07:29.27 And as you can also appreciate,
00:07:31.15 the number of nuclei stained with hematoxylin,
00:07:34.02 in blue, is increased.
00:07:36.10 That means that inflammation has set in in this mouse.
00:07:40.05 So, now we quantified our area of Oil Red O
00:07:43.00 in both these conditions.
00:07:44.22 As we found that…
00:07:46.12 when we injected immune cells from the inflamed mouse
00:07:48.24 into the immunocompromised mouse,
00:07:50.11 there was a reduction in the fat layer.
00:07:53.08 Now, this experiment proved that immune cells
00:07:55.19 are sufficient to cause a decrease in the fat layer.
00:07:58.18 But my aim was to find out,
00:08:00.10 how can I prevent the loss of the skin fat layer
00:08:03.15 in the immuno… in the inflamed mouse?
00:08:06.11 To me at that time, it looked very simple and straightforward.
00:08:10.12 I thought that injecting anti-inflammatory drugs in the inflamed mouse
00:08:15.14 should rescue the skin fat.
00:08:17.18 But little did I know…
00:08:19.11 I tried different types of anti-inflammatory drugs
00:08:21.23 at different concentrations, different time points, and different combinations.
00:08:26.06 Nothing worked.
00:08:28.08 And this led to a lot of frustration,
00:08:30.12 both for me as well as Colin.
00:08:32.24 But luckily, an immunologist, Dr. Dipayan,
00:08:35.19 visited our campus to give a talk.
00:08:38.10 Colin encouraged me to discuss my project with Dr. Dipayan.
00:08:42.14 Now, this incident highlights the importance of communicating and sharing
00:08:46.21 your ideas and research with other experts in the field,
00:08:49.27 and sometimes an expert can rescue you from a difficult situation.
00:08:54.00 After discussing my data with Dr. Dipayan,
00:08:56.22 he suggested that we should use neutralizing antibodies
00:08:59.26 to remove specific types of immune cells from the skin.
00:09:04.15 Now, the question I asked was,
00:09:06.24 which immune cell should I target to neutralize
00:09:09.28 that might be important in reducing the skin fat layer?
00:09:13.22 To answer this question, I stained for different types of immune cells
00:09:17.03 in the skin
00:09:18.16 and found out that CD4 T cells
00:09:21.08 were tremendously increased,
00:09:23.09 just at the beginning of the loss of skin fat.
00:09:26.15 As you can see here, stained in the green are CD4 T cells.
00:09:31.10 In the wild type, we can sparsely locate these CD4 T cells.
00:09:35.07 But as you look into the inflamed mouse,
00:09:37.20 you can see a lot of these CD4 T cells packed in the skin.
00:09:42.04 You can also observe the lower part of the skin,
00:09:44.14 where the fat resides,
00:09:46.09 and you can find CD4 T cells also present in the skin fat layer.
00:09:52.13 Now, this suggests that in an inflamed mouse
00:09:55.24 there is an increase in CD4 T cells.
00:09:59.13 But are these… is this increase in CD4 T cells
00:10:03.08 responsible for the loss of skin fat?
00:10:05.29 To answer this question, we used the suggestion
00:10:09.04 by Dipayan Rudra:
00:10:11.15 we used neutralizing antibodies against CD4 T cells.
00:10:16.13 So, what do these neutralizing antibodies do?
00:10:18.15 When you inject them in these mice,
00:10:20.13 they will go and bind to CD4 T cells
00:10:23.02 and cause elimination of CD4 T cells,
00:10:25.09 or in other words neutralization.
00:10:28.03 So, I first loaded the skin from inflamed mouse
00:10:32.22 injected with control onto the microscope,
00:10:35.08 and I observed that there was no skin fat, as expected.
00:10:39.24 Next, I loaded the skin section from the inflamed mouse
00:10:43.19 injected with anti-CD4 neutralizing antibodies.
00:10:46.11 Now, given the history of failed experiments with anti-inflammatory drugs,
00:10:50.26 I was anxious to know the result.
00:10:53.04 When I first looked in the microscope,
00:10:55.02 I found some blurred red staining on the skin section.
00:10:59.18 As I focused the microscope,
00:11:01.11 the blurred red staining turned into proper fat blobs,
00:11:04.23 and this experiment suggested that CD4 T cells
00:11:07.24 are responsible for loss of skin fat,
00:11:10.14 and neutralizing CD4 T cells in an inflamed mouse
00:11:13.20 can prevent that loss.
00:11:16.10 And this was a very exciting result for me,
00:11:18.19 that after a long time I was able to
00:11:22.01 finally prevent the loss of skin fat.
00:11:24.16 So, one day, me and Colin
00:11:27.12 had nothing much to do in lab,
00:11:29.10 so we decided, let’s fill tips for the lab.
00:11:32.09 After a long discussion about the beef kebabs and the briskets,
00:11:36.12 we started discussing about my project,
00:11:39.13 and Colin asked me,
00:11:41.17 what do you think is the mechanism
00:11:43.25 by which the skin fat is lost in these mice?
00:11:47.00 I quickly responded that I think it might be autophagy.
00:11:51.20 And in one of the rarest events in the cosmos,
00:11:54.28 my boss agreed with me.
00:11:58.10 So, what is autophagy?
00:12:00.10 Autophagy is a process of self-eating,
00:12:02.11 in which the cells consume the components of its own.
00:12:07.16 Now, in the case of the fat cells,
00:12:09.29 the fat cell is occupied completely with the lipid droplet…
00:12:14.05 the majority of the fat cell is occupied.
00:12:16.20 And this major lipid droplet is broken down into tiny lipid droplets,
00:12:20.07 which are taken up by lysosomes, and hence dissolved there.
00:12:24.11 So, this leads to shrinking of the lipid droplet
00:12:27.00 and shrinking of the fat cell.
00:12:29.11 I hypothesized that it might be autophagy
00:12:32.08 because CD4 T cells have the capacity to produce
00:12:37.03 factors that can induce autophagy in some cells.
00:12:40.24 But before we can test autophagy,
00:12:43.20 we need to find out,
00:12:45.16 do we see an increased autophagy in the inflamed mouse?
00:12:49.20 Do we see some evidence?
00:12:51.12 So, to find out that evidence,
00:12:53.21 we used an electron microscope.
00:12:55.19 First, we looked at a wild type skin, and we found,
00:12:59.07 around that major lipid droplet, there were a few tiny lipid droplets,
00:13:03.21 as shown by the arrowheads.
00:13:05.05 Next, we looked at the inflamed mouse
00:13:07.21 and found, around the major lipid droplet,
00:13:10.15 there were a lot of tiny lipid droplets coming out from the major lipid droplet,
00:13:13.28 suggesting there is an increase in the autophagy.
00:13:17.29 We used a second line of evidence
00:13:21.06 by staining for an autophagy marker by immunofluorescence.
00:13:24.21 So, here the autophagy marker is stained in green.
00:13:28.25 The more green punctae you see
00:13:32.12 means more autophagy.
00:13:34.00 As we can clearly see in the slide,
00:13:36.19 the inflamed mouse has increased green staining.
00:13:40.07 That means there is increased autophagy.
00:13:42.23 Now that we have two lines of evidence,
00:13:44.25 from electron microscopy and from the immunofluorescence,
00:13:49.05 it was time to test for autophagy.
00:13:52.03 So, to test if the increased autophagy
00:13:54.28 is responsible for loss of skin fat in these mice,
00:13:58.00 we injected an autophagy inhibitor.
00:14:00.14 So, once we injected the autophagy inhibitor,
00:14:02.28 we observed that loss of skin fat was prevented.
00:14:06.15 So now, this suggests that in an inflamed mouse
00:14:09.26 there is an increase in CD4 T cells,
00:14:12.25 which leads to an increase in autophagy,
00:14:15.24 and once you prevent that autophagy,
00:14:17.26 once you inhibit that autophagy,
00:14:19.25 you prevent the loss of skin fat.
00:14:21.26 So, this observation was in the engineered mouse model.
00:14:25.03 So, the beauty of studying an engineered mouse model
00:14:28.13 is that it can tell you about human pathologies
00:14:30.24 so that we can intervene in those pathologies.
00:14:34.06 It can also tell you what is happening in normal physiology.
00:14:37.20 For example, our skin continuously undergoes cyclic changes.
00:14:41.18 Remarkably, the skin fat layer
00:14:44.24 undergoes continuous expansion and shrinking,
00:14:47.11 and these cyclic changes can be divided into
00:14:51.12 growth, regression, and resting.
00:14:53.28 Growth means expansion;
00:14:55.17 regression means decrease or shrinking;
00:14:57.06 and resting means maintaining the skin fat layer at a minimum.
00:15:01.05 This is an unsolved question in skin biology —
00:15:04.13 how the skin fat layer remarkably expands and shrinks.
00:15:08.21 When we observed this pathway
00:15:11.14 in a engineered mouse model,
00:15:12.28 we thought, can we apply the knowledge
00:15:14.21 obtained from the engineered mouse model
00:15:16.17 into the physiology?
00:15:18.12 To test if the CD4 T cell or autophagy
00:15:21.16 was responsible for this shrinking
00:15:23.26 that happens in the physiology,
00:15:25.08 we gave the treatments just before the regression phase,
00:15:29.10 and collected the skin at the resting stage.
00:15:32.21 If the CD4 T cell or autophagy is responsible,
00:15:34.27 then we should see expansion of the skin fat
00:15:38.26 at the resting stage,
00:15:40.06 which would mean that regression was prevented.
00:15:43.00 So, we first used neutralizing antibodies
00:15:45.03 against CD4 T cells,
00:15:47.05 injected at the beginning of regression phase,
00:15:48.21 and collected at the resting stage.
00:15:50.22 And we found, indeed, that the skin fat layer was expanded,
00:15:54.14 which means that the regression was prevented.
00:15:57.06 Similarly, when we used an autophagy inhibitor
00:15:59.27 at the beginning of the regression phase
00:16:01.21 and collected at the resting stage,
00:16:03.09 we found that the skin fat layer was again expanded,
00:16:07.00 which again means that the regression was prevented.
00:16:11.20 To summarize, I have shown you
00:16:14.07 a non-immune function of an immune cell,
00:16:16.10 the CD4 T cell,
00:16:17.21 in causing the regression of skin fat via autophagy.
00:16:21.20 Now, I’m not here to tell you that the issue of scarring and scleroderma
00:16:25.12 has been completely solved.
00:16:27.06 What I can tell you is that CD4 T cells and autophagy
00:16:30.29 can be a good potential therapeutic
00:16:34.00 to intervene in scarring and scleroderma.
00:16:37.03 To conclude, I have shown you a pathway
00:16:39.18 in which the immune cell plays a non-immune function
00:16:42.17 in causing the shrinking of the skin fat,
00:16:44.22 and that is via autophagy,
00:16:46.17 and this takes place both in the physiology
00:16:48.27 as well as in the pathology.
00:16:51.25 So, these are the seen applications of this research project.
00:16:55.22 As for many research projects in science,
00:16:58.18 this project can also have some unseen effects.
00:17:02.05 For example, this knowledge can be tested
00:17:04.29 in different skin conditions,
00:17:06.23 such as in aging,
00:17:08.24 in which there is loss or a decrease of the skin fat layer,
00:17:11.18 which leads to wrinkling.
00:17:13.17 And a far, far fetched goal would also be to use this knowledge in obesity,
00:17:18.25 to promote autophagy and to promote a specific type of inflammation
00:17:23.07 for a controlled reduction in the body fat.
00:17:27.03 But for that, we’ll have to wait.
00:17:29.22 Thank you.

This Talk

Speaker: Edriss Yousuf

Audience:

Educators of H. School / Intro Undergrad
Student
Educators of Adv. Undergrad / Grad
Researcher
Educators

Recorded: July 2021

Talk Overview

The fat layer in our skin has the ability to expand and shrink. Yet, the regulatory mechanisms for skin fat growth and shrinking are not well understood. In this Share Your Research Talk, Edriss Yousuf describes his thesis research on the regulation of skin fat. He discovered a non-immune function of regulatory T cells and showed that they can induce autophagy in skin fat cells to decrease their lipid droplet size. These findings have implications for scarring and scleroderma, disorders which are typically associated with reduced skin fat abundance.

Speaker Bio

Edriss Yousuf

Edriss Yousuf is a PhD candidate at the Institute for Stem Cell Science and Regenerative Medicine in Bangalore, India, in the laboratory of Colin Jamora. His thesis research led to the discovery of potential therapeutics that can help prevent scarring of skin after wounding or progressive scarring during autoimmune diseases. Edriss seeks to become a… Continue Reading

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Brittany Anderton (iBiology): Producer
Eric Kornblum (iBiology): Videographer
Jiefei Yuan (iBiology): Editor
Chris George (iBiology): Graphics
Maggie Hubbard (iBiology): Graphics

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