Our Reserch Summary

In recent years, advances in molecular biology and biochemistry have begun to elucidate the pathophysiological mechanisms (molecular mechanisms that cause diseases) of various diseases. However, many intractable diseases, including neurodegenerative diseases, still lack a complete understanding of their pathophysiology at the molecular level.

In our laboratory, we are focusing on “organelle contact sites” to deepen our understanding of these diseases. Organelle contact sites are areas where different organelles come into direct contact with each other. These sites play a crucial role in the transmission of cellular information and the exchange of substances, forming highly dynamic structures. Organelle contact sites are believed to adapt their structure and function in response to changes in the cellular environment, such as stress responses or the accumulation of abnormal proteins, thereby contributing to the maintenance of cellular homeostasis.

We have previously demonstrated that the disruption of organelle contact sites formed between the endoplasmic reticulum and mitochondria is one of the major pathologies common to amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by the selective degeneration of motor neurons. Furthermore, we have successfully developed techniques to visualize and quantify abnormalities in these contact sites using protein engineering methods.

Currently, based on these findings and technical foundations, we aim to elucidate the molecular mechanisms underlying organelle contact site abnormalities in various diseases using cultured cells and mouse models, with the ultimate goal of developing future therapeutic strategies.

FOCUS

Organelle Contact Site

The endoplasmic reticulum (ER) is a membrane-bound organelle within cells that performs diverse functions such as protein modification, transport, and calcium ion regulation. The ER forms organelle contact sites, which are regions where the ER comes into direct contact with another organelle. Among the orgenelle contact sites, the contact area between the ER and mitochondria is called the “mitochondria-associated membrane (MAM)”, which is essential for mitochondrial energy production and maintainance. We have previously demonstrated that MAM disruption occurs in ALS (Watanabe et al. EMBO Mol Med 2016), that various ALS-causing genes commonly induce the MAM disruption (Watanabe et al. FASEB J 2021), and that the MAM disruption is associated with impaired protein stress responses (Watanabe et al. PNAS 2023) and mitochondrial dysfunction (Watanabe et al. Neurobiol Dis 2023).

Our Reserch Projects

A) The molecular basis of diseases focused on impaired organelle contact sites

1. Disease-specific pathogenesis associated with abnormalities in the organelle contact site

　Based on our previous research findings, we are conducting a detailed analysis of how abnormalities in organelle contact sites, particularly MAM, contribute to the onset and progression of ALS and Alzheimer's disease (AD), which is the primary cause of dementia. Specifically, we isolate the MAM from tissues of disease-model mice or cultured cells and compare its components with those of normal MAM to identify proteins responsible for the abnormalities. Additionally, we are narrowing down the functions of the MAM that are particularly involved in disease progression to clarify the association between the MAM abnormalities and the disease pathology. Furthermore, we are concurrently analyzing the involvement of other organelle contact sites and their effects on pathologies other than neurodegenerative diseases, aiming to elucidate the role of organelle contact abnormalities in various diseases.

2. Elucidation of signaling pathways responsible for organelle contact sites' maintenance

　　Organelle contact sites are known as highly dynamic structures that respond to various stressors and external stimuli. Thus, it is essential to maintain an appropriate level of the organelle contact sites. We are now studying to elucidate the intracellular signaling pathways that modulate the formation levels of organelle contact sites. Currently, we have successfully identified candidate signaling pathways that control the MAM formation through screening using our proprietary visualization and quantitative analysis tool “MAMtracker” (Sakai et al. FASEB J 2021), and are advancing detailed analyses of their mechanisms.

B) Application of Protein Enginnering

1. Development of novel reporter molecules for the organelle contact sites

Currently, technologies for visualizing and quantifying organelle contact sites, including the MAM, are advancing in various fields. The “MAMtracker” we developed is also a useful tool, but it has limitations such as being restricted to use in live cultured cells and not being suitable for tissue-level analysis. To address these challenges, we are applying protein engineering techniques to develop new reporter molecules that can be used in fixed tissues and living organisms. We anticipate that the development of this new tool will enable more comprehensive and practical functional analysis of organelle contact sites.

2. Development of novel therapeutic artificial proteins

reduction of SOD1 aggregates by Cystatin C

We have previously reported that endogenous proteins such as cystatin C (Watanabe et al. Cell Death Dis 2014) (Watanabe et al. J Neurochem 2017) and neuroglobin(Watanabe et al. J Biol Chem 2012), which possess neuroprotective effects and demonstrated therapeutic efficacy against neurodegenerative diseases. These proteins are considered promising as future therapeutic molecules. However, there is a challenge in that neurons are constrained by barriers such as the blood-brain barrier, making it difficult for externally administered proteins to reach the central nervous system. To overcome this challenge, we are currently utilizing protein engineering techniques to develop modified artificial proteins to enhance therapeutic effects and improve delivery efficiency to the central nervous system.

We are also conducting research to elucidate the pathophysiology of various diseases focused on the organelle contact sites to develop therapeutic treatments.
If you are interested in our research, please feel free to contact us at the e-mail address below.