The effect of caspase-9 in the differentiation of SH-SY5Y cells

The concealed side of caspases: beyond a killer of cells

Since the late 20th century, researchers have known that caspases are a pillar of cell death, particularly apoptosis. However, recent advances in cell biology have unraveled the multiple roles of caspases. These enzymes have an unconventional role in cell proliferation, differentiation, and invasion. As a result, caspase deregulation can fuel the fire of cancer, incite flames of inflammation, flare neurodegenerative disorders, and exacerbate skin pathologies. Several therapeutic approaches toward caspase inhibition have been investigated, but can caspase inhibitors harness the maladaptive effect of these proteases without causing significant side effects? A few studies have exploited caspase induction for cancer or adoptive cell therapies. Here, we provide a compelling picture of caspases, starting with their evolution, their polytomous roles beyond cell death, the flaws of their deregulation, and the merits of targeting them for therapeutic implications. Furthermore, we provide a deeper understanding of the evolution of caspase-related research up to the current era, pinpointing the role of caspases in cell survival and aiding in the development of effective caspase-targeted therapies.

A Non-Apoptotic Pattern of Caspase-9/Caspase-3 Activation During Differentiation of Human Embryonic Stem Cells into Cardiomyocytes

In vitro studies have demonstrated that the differentiation of embryonic stem cells (ESCs) into cardiomyocytes requires activation of caspases through the mitochondrial pathway. These studies have relied on synthetic substrates for activity measurements, which can be misleading due to potential none-specific hydrolysis of these substrates by proteases other than caspases. Hence, caspase-9 and caspase-3 activation are investigated during the differentiation of human ESCs (hESCs) by directly assessing caspase-9 and -3 cleavage. Western blot reveals the presence of the cleaved caspase-9 prior to and during the differentiation of human ESCs (hESCs) into cardiomyocytes at early stages, which diminishes as the differentiation progresses, without cleavage and activation of endogenous procaspase-3. Activation of exogenous procaspase-3 by endogenous caspase-9 and subsequent cleavage of chromogenic caspase-3 substrate i.e. DEVD-pNA during the course of differentiation confirmes that endogenous caspase-9 has the potency to recognize and activate procaspase-3, but for reasons that are unknown to us fails to do so. These observations suggest the existence of distinct mechanisms of caspase regulation in differentiation as compared to apoptosis. Bioinformatics analysis suggests the presence of caspase-9 regulators, which may influence proteolytic function under specific conditions.

Differentiating SH-SY5Y Cells into Polarized Human Neurons for Studying Endogenous and Exogenous Tau Trafficking: Four Protocols to Obtain Neurons with Noradrenergic, Dopaminergic, and Cholinergic Properties

Pathological alterations of the neuronal Tau protein are characteristic for many neurodegenerative diseases, called tauopathies. To investigate the underlying mechanisms of tauopathies, human neuronal cell models are required to study Tau physiology and pathology in vitro. Primary rodent neurons are an often used model for studying Tau, but rodent Tau differs in sequence, splicing, and aggregation propensity, and rodent neuronal physiology cannot be compared to humans. Human-induced pluripotent stem cell (hiPSC)-derived neurons are expensive and time-consuming. Therefore, the human neuroblastoma SH-SY5Y cell line is a commonly used cell model in neuroscience as it combines convenient handling and low costs with the advantages of human-derived cells. Since naïve SH-SY5Y cells show little similarity to human neurons and almost no Tau expression, differentiation is necessary to obtain human-like neurons for studying Tau protein-related aspects of health and disease. As they express in principle all six Tau isoforms seen in the human brain, differentiated SH-SY5Y-derived neurons are suitable for investigating the human microtubule-associated protein Tau and, for example, its sorting and trafficking. Here, we describe and discuss a general cultivation procedure as well as four differentiation methods to obtain SH-SY5Y-derived neurons resembling noradrenergic, dopaminergic, and cholinergic properties, based on the treatment with retinoic acid (RA), brain-derived neurotrophic factor (BDNF), and 12-O-tetrade canoylphorbol-13-acetate (TPA). TPA and RA-/TPA-based protocols achieve differentiation efficiencies of 40-50% after 9 days of treatment. The highest differentiation efficiency (~75%) is accomplished by a combination of RA and BDNF; treatment only with RA is the most time-efficient method as ~50% differentiated cells can be obtained already after 7 days.

Caspase-9-mediated cleavage of vimentin attenuates the aggressiveness of leukemic NB4 cells

Vimentin is a main type 3 intermediate filament protein. It seems that abnormal expression of vimentin is contributed to the appearance of the aggressive feature of cancer cells. So that it has been reported that malignancy and epithelial-mesenchymal transition in solid tumors, and poor clinical outcomes in patients with lymphocytic leukemia and acute myelocytic leukemia have been associated with the high expression of vimentin. Vimentin is a non-caspase substrate of caspase-9 although its cleavage by caspase-9 in biological processes has not been reported. In the present study, we sought to understand whether vimentin cleavage mediated by caspase-9 could reverse the malignancy in leukemic cells. Herein, to address the issue, we investigated vimentin changes in differentiation and took advantage of the inducible caspase-9 (iC9)/AP1903 system in human leukemic NB4 cells. Following the transfection and treatment of the cells using the iC9/AP1903 system, vimentin expression, cleavage, and subsequently, the cell invasion and the relevant markers such as CD44 and MMP-9 were evaluated. Our results revealed the downregulation and cleavage of vimentin which attenuates the malignant phenotype of the NB4 cells. Considering the favorable effect of this strategy in keeping down the malignant features of the leukemic cells, the effect of the iC9/AP1903 system in combination with all-trans-retinoic acid (ATRA) treatment was evaluated. The obtained data prove that iC9/AP1903 significantly makes the leukemic cells more sensitive to ATRA.