Intracellular cargos (organelles, vesicles, macromolecules) are driven long distances along microtubules by molecular motors (16 cargo-carrying kinesins and one cytoplasmic dynein in interphase). Microtubule-based transport influences a range of functions critical for the survival, maintenance and growth of cells. The importance of this process is emphasized in neurological diseases, where a primary hallmark are defects in microtubule-based transport and distribution of cargos.
What is the lab's goal? To understand (1) the molecular mechanisms of how, when and where these cellular cargos move on microtubules (2) how their spatiotemporal distribution affects cellular and neuronal function and (3) how microtubule-based transport goes awry in neurological diseases such as Parkinson's disease.
What is our approach? The lab uses in vitro reconstitution assays, molecular biology, cutting-edge live cell microscopy, and genetics in a variety of cell types including mammalian neurons, mammalian cell lines, and the filamentous fungus Aspergillus nidulans.
See below for more information on ongoing projects in the Salogiannis lab and check out our videos page to see intracellular movement in action!
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Cargo Movement: Adaptors and Hitchhiking
Check out this cool video of a hitchhiking peroxisome, as well as the movement of other intracellular cargos! (Image from Salogiannis and Reck-Peterson, 2017)
There are literally hundreds of cargos (including the early endosome depicted in the figure) that move long distances around the cell on microtubules. An important goal in our lab is to understand the specific mechanisms that lead to the loading, movement and offloading of these cargos.
There are two major modes of microtubule-based transport. The first (and most common) relies on cargo adaptor proteins. There are a handful of cargo adaptors, whose job is to associate with a subgroup of cargos and recruit molecular motors (left panel in figure). The identity of the motors and cargos each adaptor protein interacts with, as well as the specific regulatory mechanisms of these interactions, are largely unknown. The second mode of transport is known as hitchhiking: some cargos (including peroxisomes) move by attaching to motile endosomes at membrane-contact sites (right panel in figure). The molecular mechanisms governing these contact-site interactions are not clear. We are interested in a deeper understanding of both modes of microtubule-based transport.
Ongoing questions related to Microtubule-based transport:
(1) How is cargo-motor specificity achieved? How do cargo adaptors interact with the motors?
(2) What are the molecular mechanisms regulating peroxisome hitchhiking on early endosomes?
(3) Is hitchhiking conserved in mammalian cells?
LRRK2 and Parkinson's Disease
Parkinson's disease (PD) is characterized by resting tremors, bradykinesia and postural instability. Cellular models of PD have defects in both vesicular trafficking and distribution of various cargos. Although it primarily affects dopaminergic neurons in the substantia nigra, it is well-appreciated that PD is a non-cell autonomous neurological disease with hallmarks of neuroinflammation. The primary mechanisms leading to aberrant vesicular trafficking and the cell-types that are most critical for PD pathophysiology are under intense investigation.
Leucine-rich repeat kinase-2 (LRRK2) is the most commonly mutated gene in familial Parkinson's disease. Importantly, LRRK2-linked PD has cellular and organismal features similar to idiopathic cases of PD: First, individuals with LRRK2-linked PD have symptoms indistinguishable from idiopathic cases. Second, LRRK2 is expressed in many cell types including neurons, astrocytes, microglia, and peripheral immune cells. Gene expression of LRRK2 is induced by inflammation. Third, LRRK2 is a kinase that phosphorylates a subset of Rab GTPases. Rabs are major directors of vesicular trafficking critical for the coordination of membrane fusion and the sorting of cellular components. We found that the movement of Rab-marked vesicles is altered in cells expressing pathogenic mutations in LRRK2 and we also found that LRRK2 acts as a roadblock in vitro to block the movement of microtubule-based motors (Check out our videos page to see the movement of Rab-marked vesicles!).
Ongoing questions related to LRRK2:
(1) What are the molecular mechanisms leading to inflammation-induced gene expression of LRRK2?
(2) How does the pathogenic expression of LRRK2 affect Rab movement and downstream biological function in both neuronal and non-neuronal cell types?