The genetic background together with environmental factors and lifestyle are key contributors to the health of an individual. Genetic background is inherited and irreversible unless mutations occur. However, lifestyle habits (i.e., diet, stress, physical activity, smoking, and alcohol consumption) are modifiable factors that contribute to health or disease by affecting methylation of DNA, which regulates transcription of genes.

One of the most relevant lifestyle habits for health is maintaining adequate vitamin D levels in the body as vitamin D promotes calcium and phosphate absorption, supports the nervous and immune system function, and protects bone and muscle structure. Extreme low levels of vitamin D, vitamin D deficiency, has become a global public health concern, especially in the elderly population as vitamin D deficiency can lead to several health problems such as bone fracture, decreased muscle strength, cardiovascular and autoimmune diseases, depression, and breast, pancreatic, and prostate cancer.

Prostate cancer is an uncontrolled growth of cells within the prostate gland in the male reproductive system. Human prostate carcinomas are sensitive to androgens, and hormonal ablation therapy gives a temporary remission, followed by a relapse to an androgen-insensitive state. This indicates that steroid hormones, especially androgens, play a significant role in human prostatic carcinogenesis. The molecular effect of vitamin D as a steroid hormone and which steroid hormone receptor (SHR) mediates this effect are not fully understood.

This research project aims to increase our knowledge about SHRs, primarily the vitamin D receptors, in both health and disease, focusing on genomic, epigenomic, and transcriptomic perspectives in healthy elderly individuals and prostate cancer cells.

The results from the studies in this thesis could help us understand the importance of a healthy lifestyle, which includes vitamin D for health, where we found specific methylation markers involved in the down-regulation of cancer pathways that are associated with high physical activity and vitamin D supplementation. We have further confirmed that SHRs rarely work in isolation but rather as a crosstalk at the genomic level to regulate their transcription. Hopefully, this will help clarify the modulation of transcriptional responses in SHRs and explain the development of steroid hormone-dependent cancers such as prostate cancer. Last, but not least, we revealed that genetic and transcriptional markers are associated with the putative vitamin D receptor the protein disulfide isomerase family A member 3 (PDIA3). The genetic markers were detected in a healthy elderly population under vitamin D supplementation. The transcriptional markers, PDIA3, and a novel discovered isoform of PDIA3 (PDIA3N) were related to the androgen and cancer stage of prostate cancer cells and therefore are proposed as candidate markers for clinical diagnosis of prostate cancer.

Altogether, these findings support the relevance of studying vitamin D and steroid hormone receptors, especially the PDIA3 receptor, to understand some of the factors related to healthy aging and the etiology and progression of prostate cancer.