Biology 133 lecture AY 2021- 2022

Good day, Ma'am Leonardo. Here are our answers to your questions po:

1. Are there mechanical or chemical factors that could lead to accidentally upsetting hypoxic conditions to the detriment of development of the cardiovascular system?

One way of upsetting normal hypoxic conditions is by inducing severe hypoxia (5-7.5% oxygen) through uterine constriction and bradycardia. Various activities can lead to the phenomenon, one of which is the administration of drugs with almokalant and dofetilide that deliberately slow or stop the embryonic heart for a short period of time. It was also discovered that phenytoin caused a concentration-dependent slowing and arrhythmia of the embryonic heart of in vitro-grown rat embryos (Webster & Abela, 2007).

Constriction of the uterine vessel is one mechanical factor influencing hypoxic conditions. Cocaine use in pregnancy, for example, can cause severe uterine artery constriction that could lead to hypoxia-related malformations. In this case, the uterus and the enclosed embryos are deprived of blood for the duration of the constriction, resulting in severe hypoxia. Surviving fetuses may have malformations, such as heart defects and situs inversus (Webster & Abela, 2007).

2. Would a slight change in hypoxic levels bring about abnormal development? Up to what stage in the cardiovascular development should the hypoxic condition be maintained?

Modest degrees of changes in hypoxia are tolerated by the embryo, but more extreme alterations in hypoxia levels will result in a variety of developmental changes. For example, inadequate exposure to normal hypoxia lowers the expression of essential genes required for heart and vascular development, like that of which encodes for hypoxia-inducible factor or HIF. Furthermore, chronic exposure to moderate abnormal hypoxia can lead to programming of cardioprotective genes, which may impair the capacity of heart to adjust to stresses later in life, and more severe abnormal hypoxia can have a substantial impact on the development of embryonic cardiomyocytes, which can lead to cardiomyopathy (Patterson and Zhang, 2010).

Dunwoodie (2009) posited that modification of the HIF activity up to the chamber formation stage is considered to be lethal on the development of the cardiovascular system. It was discovered in the same study that this change resulted in the following effects: the morphogenesis is halted at the looping stage, there is occurrence of hypoplasia, absence of trabeculation, and impaired neural crest cell migration. Thus, it is important that for a normal cardiovascular system development that the hypoxic condition is maintained up to the chamber formation stage,

References:
Dunwoodie, S. L. (2009). The Role of Hypoxia in Development of the Mammalian Embryo. Developmental Cell, 17(6), 755–773. https://doi.org/10.1016/j.devcel.2009.11.008

Patterson, A. J., & Zhang, L. (2010). Hypoxia and fetal heart development. Current molecular medicine, 10(7), 653–666. https://doi.org/10.2174/156652410792630643

Webster, W. S., & Abela, D. (2007). The effect of hypoxia in development. Birth defects research. Part C, Embryo today : reviews, 81(3), 215–228. https://doi.org/10.1002/bdrc.20102

Good evening, Kiara!! Thank you for these questions and here are our answers:

1. What are the other nematodes, invertebrates, or species that possess these proteins?

According to studies, orthologues of HIF, PHD, and VHL have been discovered in a variety of invertebrates, mammals, and even the simplest animals, the Placozoa. The HIF dependent hypoxia signaling system, for example, has been described in a number of invertebrates, including drosophila, and is thus thought to be shared by arthropods and bilaterians. This pathway's components have also been identified in mammalian cells (Fisher & Burggren, 2007). Even the simplest animal, Trichoplax adhaerens, has a hypoxia-inducible transcription factor pathway that regulates oxygen sensing (Loenarz et al., 2010).

2. Did they have a similar strategy as C. elegans in surviving or coping with oxygen deprivation?
As discussed in the video, several factors such as size, surface area to mass ratio, and specialized affect animal oxygen regulation and thus their coping mechanisms in the face of hypoxia. However, because the HIF pathway is the primary mechanism these animals use to sense and regulate oxygen levels, they still share similarities in their coping mechanisms. For example, a study of Drosophila melanogaster exposed to different O2 concentrations revealed that the fruit fly, like Caenorhabditis elegans, reduces its metabolic rate when subjected to hypoxia (van Voorhies, 2009).
3. Were these organisms also investigated for hypoxia's role in the development of the cardiovascular system?
Yes, we discovered studies that looked into the role of hypoxia in the development of the cardiovascular system in other organisms.
For example, Dunwoodie (2009) discovered that HIF activity is absolutely required for normal heart development in his study titled "The Role of Hypoxia in Development of the Mammalian Embryo." Furthermore, the study found that cellular hypoxia and HIF component expression occur during the heart development process.

References:
Dunwoodie, S. L. (2009). The Role of Hypoxia in Development of the Mammalian Embryo. Developmental Cell, 17(6), 755–773. https://doi.org/10.1016/j.devcel.2009.11.008

Fisher, S. A., & Burggren, W. W. (2007). Role of Hypoxia in the Evolution and Development of the Cardiovascular System. Antioxidants & Redox Signaling, 9(9), 1339–1352. https://doi.org/10.1089/ars.2007.1704

Loenarz, C., Coleman, M. L., Boleininger, A., Schierwater, B., Holland, P. W. H., Ratcliffe, P. J., & Schofield, C. J. (2010). The hypoxia‐inducible transcription factor pathway regulates oxygen sensing in the simplest animal, Trichoplax adhaerens. EMBO Reports, 12(1), 63–70. https://doi.org/10.1038/embor.2010.170
van Voorhies, W. A. (2009). Metabolic function in Drosophila melanogaster in response to hypoxia and pure oxygen. Journal of Experimental Biology, 212(19), 3132–3141. https://doi.org/10.1242/jeb.031179

Hi Marcus!! Thank you for taking the time to watch our presentation and to ask questions about it.

For the first question, we were only able to find one study about a method which can directly measure oxygen consumption in intact cells. The method is called open-air method and even though it involves a simple process, measuring direct oxygen demands and consumption rate is still considered to be problematic since there is still a lack of more inclusive methods for it. For example, the open-air method can only be used when the O2 consumption rate and demands in the cells are ensured to not change while in the process of measurement. This poses a lot of problems due to the fact that in nature, cell demands on O2 are generally variable (Mamchaoui & Saumon, 2000).

For the next question, we were able to find different therapeutic purposes for the deletion of HIF-α genes. In a study conducted by Thiel et al. (2007), targeted deletion of HIF-α genes in T cells was able to prevent their inhibition in hypoxic inflamed tissues and was able to enhance the survival of septic mice. T cells are significant contributors in anti-bacterial responses of the body. Since they are inhibited by HIF-α in hypoxic and inflamed tissues, deletion of HIF-α genes was able to improve their recruitment when the organism is exposed to cell-damaging and/or disease-causing environments. In addition to this, HIF-α deletion was also found to protect the test organism from radiation-induced enteritis. This was considered as a significant discovery which may result in crucial advancements in treating gastrointestinal injuries (Toullec et al., 2018).

References:
Mamchaoui, K. & Saumon, G. (2000). A method for measuring the oxygen consumption of intact cell monolayers. American Journal of Physiology-Lung Cellular and Molecular Physiology, 278(4), L858–L863. doi:10.1152/ajplung.2000.278.4.L858

Thiel, M., Caldwell, C. C., Kreth, S., Kuboki, S., Chen, P., Smith, P., Sitkovsky, M. V. (2007). Targeted Deletion of HIF-1α Gene in T Cells Prevents their Inhibition in Hypoxic Inflamed Tissues and Improves Septic Mice Survival. PLoS ONE, 2(9), e853. doi:10.1371/journal.pone.0000853

Toullec, A., Buard, V., Rannou, E., Tarlet, G., Guipaud, O., Robine, S., Iruela-Arispe, M., François, A., Milliat, F. (2018). HIF-1α Deletion in the Endothelium, but Not in the Epithelium, Protects From Radiation-Induced Enteritis. Cellular and Molecular Gastroenterology and Hepatology, 5(1), 15–30. doi:10.1016/j.jcmgh.2017.08.001

Hello Regina!!

So far we weren't able to see any particular congenital heart disease that is directly caused by the deletion of HIF-α genes. However, we discovered that HIF-α gene deletion can promote Kras-driven lung tumor development. This is because HIF-α genes actually induces the expression of tumor-suppressor genes, thereby their deletion resulted to the reduction on the number of these genes which are responsible for suppressing tumor development.

Reference:
Mazumdar, J., Hickey, M., Pant, D., Durham, A., Sweet-Cordero, A., Vachani, A., Jacks, T., Chodosh, L. A., Kissil, J. L., Simon, M. C., Keith, B. (2010). HIF-2 deletion promotes Kras-driven lung tumor development. Proceedings of the National Academy of Sciences, 107(32), 14182–14187. doi:10.1073/pnas.1001296107