Poster H5 - Mechanical stress Induced Connexin 43 Hemichannel Activation Regulates Breast Cancer Bone Metastasis and Modulates EMT Marker Expression

Friday, October 25, 2024

3:30 PM - 4:30 PM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Alba Chocron (she/her/hers)

Undergraduate Student
University of Texas at San Antonio
San Antonio, Texas, United States

Co-Author(s)

Xuewei Wang

Graduate Student
UT Health San Antonio, Texas, United States

Primary Investigator(s)

JJ

Jean Jiang

Primary Investigator
UT Health San Antonio, United States

Introduction: Breast cancer (BC) is the most common cancer and the second leading cause of cancer-related deaths among women. The bone is a frequent site of metastasis for breast cancer. Osteocytes, a dominant type of bone cell, have a high expression of Connexin 43 (Cx43), which can form gap junctions (GJs) for cell-cell communication or hemichannels (HCs) for interactions with the extracellular environment. While previous studies have shown that mechanical loading-induced opening of Cx43 HCs can reduce the size of metastasized breast cancer tumors, the specific role of osteocytes Cx43 HCs in breast cancer progression has not been extensively studied. Thus, we investigated the expression of Alpha-Smooth Muscle Actin (α-SMA), a marker of epithelial-mesenchymal transition (EMT), in breast cancer bone metastatic models. Our findings indicate that mechanical stress-induced activation of osteocytes Cx43 HCs modulates the bone microenvironment from being tumor-supportive to tumor-suppressive, leading to a reduction in α-SMA-positive cells in bone metastatic breast cancer tumors.

Materials and

Methods: To further investigate how Cx43 HCs regulates bone microenvironment of tumor growth, we used wildtype (WT) and transgenic mice (WT mice with both GJs and HCs present, R76W mice with only HCs present, and Δ130-136 mice with neither GJs nor HCs present). The mice were inoculated with Py8119 breast cancer cells in both tibiae following two weeks (5 minutes/day, 5 days/week) of mechanical loading on the left tibia. After four weeks of tumor growth, both tibiae with tumors were paraffin-sectioned and underwent immunohistochemistry staining (IHC). Alpha-Smooth Muscle Actin (α-SMA), an epithelial-mesenchymal transition (EMT) marker closely related to cancer progression and metastasis, was stained in the section samples.

Results, Conclusions, and Discussions: We used sodium citrate buffer or trypsin as an antigen retrieval reagent, finding that sodium citrate buffer unmasked the antigen more effectively. Hematoxylin staining allowed us to clearly visualize tumor location, revealing that WT and R76W mice with activated HCs exhibited smaller tumor sizes in the pre-mechanically loaded tibia compared to the unloaded side, consistent with our previous study. More α-SMA marker-positive cells were counted in the unloaded tibia. However, Δ130-136 mice without activated HCs exhibited similar tumor sizes and α-SMA-stained cell numbers in both pre-loaded and unloaded tibiae. Overall, our results suggest that the opening of Cx43 HCs holds promise as a therapeutic target for suppressing breast cancer bone metastasis and progression.

Acknowledgements (Optional):