Metabolic interplay

fimmu-08-00248-g001
Renner K et al. Front Immunol. (2017)

I recently came across this figure that shows the key metabolic processes that dictates an immune cell behavior and function. Biochemists and pharmacologists sometimes focus on one or two key pathways in a disease model and forget that proteins don’t function in isolation. Protein networks are complex pathways with many overlays. A drug designed to inhibit or activate a specific protein can also affect other proteins in the connected pathways. This figure is focussed on an immune cell (natural killer cell) and its interaction with a tumor cell. The interplay between the different metabolic pathways applies to all kinds of cells in the body.

This figure is also quite interesting to me because I have been studying the arginase-1 (Arg1) pathway in microglial cells and this gives me a brief overview of where my study lies in the spectrum of key cellular metabolic pathways. Arg1 is an enzyme that metabolizes L-arginine to L-ornithine and urea in the urea cycle. With the help of ornithine decarboxylase (ODC), L-ornithine further makes polyamines that are important (? – it depends) for cell growth and survival (? – it depends). I think it is quite interesting to see how Arg1 and ODC would dictate the phenotypes of the microglial cells in the brain. Microglia are the brain’s resident immune cells – they chew up all the toxic stuff and get rid of them (this is known as phagocytosis). We have always studied these cells based on their two active states (M1 or M2). There has been evidence in the recent years to show that these cells in fact may exhibit multiple activated states (not just M1 and M2). Just like many immune cells in the body that exhibit a heterogenous phenotype, microglia in the brain may be no different. I’m curious if Arg1 and ODC may be involved in regulating a similar mechanism in microglial cells during neurodegeneration..

Source: Renner K., Singer K., et al. Metabolic Hallmarks of Tumor and Immune Cells in the Tumor Microenvironment. Front Immunol. 2017; 8: 248.

 

It’s brain awareness week!

Hello all!  I wanted to take a few minutes to write something for the brain awareness week. This is important to me because my research focusses on understanding the role of the immune system in the brain. For a very long time, the brain was thought to be an “immune privileged” organ i.e., it was thought that the brain is protected from all the peripheral insults and that it is “divorced” from the rest of the body. In 2015, it was shown that there exists certain lymphatic vessels that connect the CNS to the rest of the body (1). The lymphatic system carries immune cells through a network of vessels and tissues; it connects the bloodstream and tissues in order to remove dead cells and other debris. The discovery of the new “glymphatic system” has opened new avenues to study the connection between the brain and the rest of the body. This is especially helpful in understanding the role of the peripheral immune system on the CNS during infections, injury, and other disease insults.

glymphatic system
Old lymphatic system (left) and newly discovered lymphatic system in the CNS (right). Source: University of Virginia Health System

My work focusses on a specific cell type in the brain known as microglia which are are the resident macrophages of the CNS (they eat up and clear out the bad stuff in the brain like dead cells and mis-folded proteins). Microglia are the only known immune cells of the brain. Compared to all that’s known about the cells of our body’s immune system (B cells, T cells, NK cells, neutrophils, basophils, Treg cells, MDSCs, TH1, TH2, and many many more with several subtypes of each cell), it is safe to say that cells of the CNS are poorly understood. My efforts are focussed towards understanding the role of microglial cells in neurodegenerative diseases such as Alzheimer’s Diseases (AD) , Parkinson’s Disease (PD), Multiple Sclerosis (MS), etcetera. These diseases are characterized by mis-folded proteins that aggregate in the different regions of the brain tissues causing the neurons to degenerate and eventually die. The microglial cells in these disorders play a major role in disease progression by regulating many pathways involved in cell-cell communication, cell survival, and cell death. This is a relatively new and an exciting area of study with many missing links and questions to be answered. I will try my best to keep this space alive with updates and stories! In the meantime, here’s a fun read on Leonardo da Vinci’s contributions to neuroscience: http://www.sciencedirect.com/science/article/pii/S0166223600021214

And here’s a 1504-1506 drawing of the human brain by da Vinci:

Leonardo da Vinci's contributions to neuroscience
In the upper figure, the three ventricles are labeled imprensiva (anterior ventricle, corresponding to the paired lateral ventricles), senso comune (third ventricle), and memoria (posterior or fourth ventricle). Below the ventricles, seven pairs of cranial nerves are shown. The lower figure shows a human head in an exploded view, with the skull raised over the brain and from the head. Source: 

Sources:

  1. Louveau A, et al. Structural and functional features of central nervous system lymphatic vessels. Nature. 2015;523(7560):337–341. doi: 10.1038/nature14432.

The Human Kinome

The entire set of 518 protein kinases in the human genome makes up one of the largest of all human gene families. These enzymes catalyze the phosphorylation of proteins, specifically serine/threonine and tyrosine residues – an important reaction that regulates key cellular functions like cell division, metabolism, and apoptosis in normal and disease states. This makes kinases key therapeutic targets in several diseases such as cancer, neurodegeneration, behavioral disorders, diabetes, and cardiovascular diseases. Interestingly, both the labs that I’ve been in so far are focussed on kinases involved in pancreatic/prostrate cancer and GPCR signaling in the light of alcohol/drug addiction. Leaving this nice phylogenetic tree here as a reminder and reflection of kinome research!Map of the Human Kinome

Orientation week: What do I want out of grad school?

The first week of grad school was intense and exhaustive with all kinds of information being tossed at us from all directions. We started off with a formal introduction to the school, the department, and all the resources available at our disposal like the libraries, mentors, health benefits, and so on. Besides all this, a main objective of the orientation week was to decide the first two labs that we are interested to rotate in. The process involved meeting with several professors, going on lab tours, meeting other grad students and evaluating if a lab was a good fit for us or not. Although I knew the direction of research I wanted to pursue, discovering so many options and learning about cool new research areas left me wondering if I really knew what I wanted to be doing for the next five years! Right now, I feel like a first grader starting school for the first time and constantly being exposed to many things I never knew existed.

Grad school 101 - What I don't know
Grad school 101 – What I don’t know

Being in a big umbrella program, there are ten different training groups to choose from. First year graduate students pick four labs within any of the groups to rotate in during their first year. This is very different from a departmental graduate program where a student can only rotate in labs within that respective department. After all the decisions and evaluations, I have chosen my first two labs for the semester and I am looking forward to be officially starting next week.

This process has made me question some decisions that I’ve taken in the last couple of years. “What do I want out of grad school?” seems to be the most significant one. Before beginning my journey, I knew that I wanted to train to be a good scientist, learn how to think, develop skills unique to my field, master techniques that will make me employable, learn how to learn, and be an overall well rounded researcher. Now I’m not sure if there is a definite answer to the question. It is something that I’d have to figure out on-the-go.