Revealing the secrets of the lysosome

Research material stored in nitrogen

Lysosomal function and stability

Lysosomes are acidic organelles that are critically involved in a number of physiological processes including macromolecule degradation, endocytosis, autophagy, exocytosis and cholesterol homeostasis.

Lysosomen, skiss på whiteboardThe lysosome contains over 50 different hydrolases responsible for its degradative function and a single membrane surrounds it, which is heavily glycosylated to protect other cellular compartments from its hydrolytic enzymes. Different stimuli can cause lysosomal membrane permeabilization (LMP) that results in leakage of lysosomal content into the cytosol. Depending on the grade of release this can cause apoptosis or necrosis. The lysosomal stability is dependent on its membrane composition. 

The aim of our research is to elucidate how lysosomal functions are regulated in normal cells and how they are affected in different pathological conditions. In particular the aim of our ongoing projects is to:

  • Investigate the lysosomal stability and how its contents are released
  • Elucidate the role of lysosomes in cancer cells 
  • Lysosomal participation during UV-induced effects in skin cells
  • Develop a drug delivery system to target the lysosomes

Understanding physiological processes in biochemical and molecular details not only offers insight into disease pathogenesis, but also permits the development of new diagnostic and prognostic tools, as well as the design of novel therapeutic compounds. Lysosomes are key components of many cellular processes, which make them attractive therapeutic targets. Future strategies to manipulate lysosomal function might be of great benefit for common diseases such as cardiovascular diseases, cancer, and neurodegenerative disorders. 

Lysosomes in disease

 
The Karin Öllinger research group.
Photo: Thor Balkhed
As many cellular functions involve the lysosomal compartment lysosomal disturbance has a profound impact on homeostasis. Therefore, it is not unexpected that lysosomal dysfunction causes and contributes to many diseases. Lysosomes have a central role in lysosomal storage disorders and increasing evidence indicates that lysosomes are involved also in more widespread diseases, such as cancer, and neurodegenerative diseases. Lysosomal biogenesis is regulated by transcription factors EB (TFEB) and E3 (TFE3), which are activated during starvation. Due to the essential role of lysosomes in autophagy, lysosomal dysfunction impairs this process, thereby contributing to disease. 

Lysosomal storage disorders

KvävgasförvaringPreserving cell cultures in liquid nitrogen.
Photo: Thor Balkhed

Lysosomal storage disorders represent a class of inborn pathologies characterized by the accumulation of material in lysosomes. These conditions are caused by the absence or reduced activity of lysosomal proteins, which results in the lysosomal accumulation of substances dependent on these particular proteins. The massive accumulation of substances affects the function of lysosomes and other organelles, resulting in secondary changes, such as impairment of autophagy, mitochondrial dysfunction, and inflammation. Lysosomal storage disorders frequently involve the central nervous system, where neuronal dysfunction or loss results in mental retardation, progressive motor degeneration, and premature death. 

Neurodegenerative disorders

Correct autophagic function is essential for cells, particularly for neurons, which rely on autophagy for survival, and the inactivation of crucial autophagy genes in mice results in severe neurodegeneration. Because lysosomal dysfunction is associated with many degenerative disorders, therapeutic interventions aiming at restoring lysosomal function may be useful for the treatment of e.g., Alzheimer’s and Parkinson's diseases. 
Our objectives in this field are to
  • Identify proteins involved in the control of lysosomal stability and function
  • Evaluate the effect of different treatments on lysosomal stability
  • Investigate lysosomal stability in lysosomal storage disorders
  • Study the involvement of genes regulated by TFEB/TFE3 in lysosomal stability
Our projects investigating lysosomal stability will contribute to finding strategies how to increase lysosomal degradation and clearance and might thus be useful in both neurodegenerative diseases and lysosomal storage disorders. 

Lysosomes in cancer

Cultivation of cells is the hub of our research.
Rapidly dividing cells, such as cancer cells, are highly dependent on effective lysosomal function and dramatic changes in lysosomal volume, composition, and subcellular localization occur during transformation and cancer progression. In a wide variety of cancers, cathepsins are highly upregulated and mislocalization results in secretion of cathepsins. Secretion of proteolytically active cathepsins to the extracellular space might stimulate angiogenesis, tumor growth, and invasion. In addition, secretion of lysosomal glycosidases facilitates extracellular matrix (ECM) degradation. Increasing our understanding of these changes will result in novel strategies to target the lysosomal compartment for use in future cancer therapies. 

Our main purpose is to:

  • Elucidate the impact of release of lysosomal constituents from cancer cells on intercellular communication and invasion through extracellular matrix degradation.
  • Compare lysosomal alterations in cancer cells with corresponding normal cell types to characterize tumor-mediated alterations. 

Implications of UV-irradiation for initiation and invasion of malignant melanoma

Ultraviolet (UV) irradiation is both mutagenic and mitogenic in skin cells and thereby considered as a complete carcinogen. Our overall purpose is to study UV-induced cell damage, to identify key signaling pathways for senescence and transformation of melanocytes to premalignant cells, and to identify factors that facilitate invasion of melanoma. In order to increase our knowledge of the complex interplay between the different cells in epidermis, we use co-cultures of reconstituted epidermis and evaluate the effect of different wavelengths of the UV spectra.

UV-induced effects in melanocytes and keratinocytes

ForskningsillustrationImmunocytochemical staining of cathepsin K (green),
LAMP-2 (red) and nuclei (blue) in melanoma cells.
Recently we found that UVA irradiation caused plasma membrane damage that was rapidly repaired by lysosomal exocytosis. This process results in release of lysosomal content outside the cell and we are presently studying the effects of such release for proliferation and intra- as well as intercellular signaling. An additional interest of our group is to study the effect of lysosomes and melanosomes in the cross talk between the melanocytes and keratinocytes in the skin during UV irradiation.

Our aims are to:

  • Study signaling pathways activated by UVA- and UVB-irradiation using gene expression profiles from apoptotic and surviving cells, respectively.
  • Study the epigenetic alteration in senescent melanocyte and identify diagnostic markers to differentiate between benign nevi, dysplastic nevi and melanomas. 
  • Characterize the interplay between keratinocytes and melanocytes involving exchange of extracellular vesicles during UVA- and UVB-irradiation.
  • Study UVA-induced plasma membrane damage and the effect of lysosomal exocytosis as a repair mechanism. 

Targeting of lysosomes 

The delivery of compounds into the lysosomes stands as an attractive therapeutic approach because of the direct involvement of these organelles in specific cell functions and also because they are the last step in the endocytic internalization pathway.  In lysosomal storage diseases, where lysosomal enzymes are defective, efficient delivery of these enzymes could be used to restore lysosomal function. In a more general view, delivery of specific drugs into the lysosomes could turn useful to regulate their degradation activity and their stability or, provided that there is a mechanism to permeabilize the lysosomal membrane, to target other cell compartments. This could find application in a wide range of pathological conditions ranging from neurodegenerative disorders to cancer.

Using a physicochemical approach we are studying MSDH, a lysosomotropic amphiphile, which is able to induce lysosomal membrane permeabilization. We have shown that this amphiphile forms large vesicles that spontaneously disassemble at low pH and that can be efficiently loaded with a cargo. 

Our objectives are to: 

  • Identify the mechanism by which MSDH targets the lysosomes 
  • Understand the process by which MSDH induces lysosomal membrane permeabilization 
  • Using MSDH to design a carrier that delivers compounds into the lysosomes
  • Tailoring the MSDH-based carrier to achieve controlled lysosomal membrane permeabilization 

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