Welcome to another HPA image of the week! This week we take a look at another member of the vesicle family, the lysosomes.

In a way, lysosomes can be thought of as the recycling plants of your cells. Lysosomes are small membrane bound vesicular organelles that degrade biomolecules within your cells so that the materials in these molecules can be recycled and used for other cellular processes. Often these biomolecules come from vesicles known as endosomes that bring in materials from outside your cells, however lysosomes are also known to degrade other organelles, and products from within the cell. The lysosome does this utilizing a variety of enzymes which work within an an acidic environment (pH = 5), meaning that the cell has to constantly work to maintain the acidity of this compartment (The Cell: A Molecular Approach. 2nd edition.).

Figure 1 is an image of TMEM192 (green) together with a DNA marker, DAPI (blue). This protein is found in the membrane of lysosomes and this sample shows the staining in U-2 OS human osteosarcoma cells. To confirm that this staining is of a lysosome and not another vesicular compartment, the cells were co-stained for LAMP-1, a well known lysosomal marker. LAMP-1 (red) and TMEM192 (green) can be seen together in figure 2 below. When the two appear in the same position we see the yellow color which is present in nearly all the lysosomes.

This method of co-staining is a common way of confirming specific localization of stainings, but it is important to note that this does not indicate the the antibody is specific (that it binds only) to the protein we are targeting.

As mentioned, lysosomes are important for cellular processing of materials, and disorders in lysosomal enzymes can lead to improper degradation of biomolecules. This can cause a buildup of excess materials and lead to disease (Agamanolis D.). This family of diseases, termed lysosomal storage disorders or LSDs, can be caused by disorders in any of the nearly 50 lysosomal enzymes used to break down biomolecules in your body and symptoms range from mild to severe. Here is a list of diseases and symptoms of some of the known LSDs (National Organization for Rare Disorders). Though each LSD is itself rather rare, it is estimated that 1 in 5000 people are affected by some form of LSD, many of which are hereditary.

We would like to thank all the members of the Subcellular Human Protein Atlas who generate these images and especially to Hanna Hassan, a masters student in our group for contributing the images for this article about lysosomes.

Devin Sullivan