Doctor of Philosophy (PhD)
Pathology & Microbiology
Bone metastasis is one of the major clinical concerns that causes skeletal related malignancies and increased mortality. Bone is one of the preferred sites for metastatic prostate cancer. The metastatic prostate cancer cells interact with bone cells (osteoblasts and osteoclasts) resulting in an imbalance in the bone homeostasis leading to increased activation of osteoblasts over osteoclasts. Our preliminary data indicated a non-tyrosine kinase receptor Neuropilin 2 (NRP2) is expressed in osteoclasts induced by metastatic prostate cancer cells and acts as a negative regulator of osteoclast differentiation and function. We hypothesize that prostate cancer -induced NRP2 expression in osteoclasts is necessary for low osteolytic activity and thus favors an osteoblastic lesion in prostate cancer bone metastasis.
Early experimentation discussed in my first section of my thesis demonstrated an increase in NRP2 expression in osteoclasts induced by RANKL and M-CSF and in PC3 and LNCaP C4-2B conditioned media (CM). TRAP staining and activity confirmed the differentiation of osteoclasts under these conditions. Interestingly, depletion of NRP2 and treatment with either in RANKL and M-CSF or LNCaP C4-2B CM exhibited a drastic increase in osteoclast differentiation and function. An increase in expression of osteoclastic genes following NRP2 depletion in RANKL and M-CSF and LNCaP C4-2B CM was also detected. However, NRP2-depleted osteoclast precursors when treated with PC3 CM showed no change in osteoclastogenesis. It is important to note that LNCaP C4-2B promotes mixed bone lesions, which inclines more toward osteoblastic lesion, while PC3 promotes predominantly osteoclastic bone lesions. These findings therefore advocate a role of NRP2 in inhibiting osteoclastic activity in PCa bone metastasis with mixed lesions and that osteolytic PCa evades NRP2 inhibition.
In the second section of my dissertation, we elucidated the molecular mechanisms through which NRP2 regulates osteoclast differentiation and function in normal bone and in LNCaP C4-2B CM. Our studies suggest that NRP2 regulates the expression and translocation of NFATC1 which is a crucial osteoclastic transcription factor. Additionally, NRP2 controls NF-κB in the normal bone. These data imply that NRP2 restricts the translocation of critical transcription factors to regulate osteoclasts in prostate cancer bone metastasis.
The last part of my dissertation addressed how PC3 CM-induced OCs escapes the inhibition of NRP2. Presence of GM-CSF resulted in a delay in the differentiation and fusion of osteoclasts in RANKL and M-CSF and LNCaP C4-2B CM. It can be deduced that secretion of GM-CSF by PC3 CM may regulate the differentiation and fusion of osteoclasts and thereby escapes the regulation of NRP2.
Altogether, we report that NRP2 functions as a negative regulator of osteoclasts in prostate cancer bone metastasis but is rendered ineffective in osteolytic lesions. Hence, an insight into the regulation of NRP2 in osteoclasts can aid in the development of new and effective therapeutic strategies for the treatment of prostate cancer bone metastasis.
Polavaram, Navatha S., "Elucidation of the functions of Neuropilin 2 in osteoclasts in promoting prostate cancer bone metastasis." (2018). Theses & Dissertations. 269.