TMEM65, a mitochondrial inner-membrane protein [5], is essential in regulating mitochondrial calcium (mCa2+) efflux. It interacts with the mitochondrial sodium-calcium exchanger NCLX, enhancing sodium-dependent mCa2+ efflux, which is crucial for maintaining the balance of mCa2+ uptake and efflux, thus regulating ATP production and cellular homeostasis [2,4]. It also seems to be involved in signaling pathways such as the PI3K-Akt-mTOR pathway [1].

In loss-of-function studies, knockdown of Tmem65 in mice promotes mCa2+ overload in the heart and skeletal muscle, impairing cardiac and neuromuscular function [2,4]. In the heart, disrupting Tmem65 function leads to impaired intercalated disc structure, abnormal cardiac electrophysiology, and ultimately cardiomyopathy [3]. In gastric cancer, silencing TMEM65 in GC cells suppresses cell proliferation, migration, invasion, and tumor growth both in vitro and in vivo, and VNP-encapsulated TMEM65-siRNA significantly inhibits tumor growth in subcutaneous xenograft models [1]. Depletion of TMEM65 in human cultured cells leads to oxidative stress, apoptosis, induction of mitochondrial unfolded protein response, and upregulation of mitochondrial protein import receptor TOMM22 [6].

In conclusion, TMEM65 plays a vital role in maintaining mitochondrial calcium homeostasis and normal physiological function of the heart and skeletal muscle. Its dysregulation is associated with cardiomyopathy and gastric cancer. The use of gene knockout or knockdown mouse models has been instrumental in revealing these functions and disease associations, providing potential therapeutic targets for related diseases.

References:

1. Shi, Lingxue, Wang, Xiaohong, Guo, Shang, Yu, Weifang, Yu, Jun. 2024. TMEM65 promotes gastric tumorigenesis by targeting YWHAZ to activate PI3K-Akt-mTOR pathway and is a therapeutic target. In Oncogene, 43, 931-943. doi:10.1038/s41388-024-02959-9. https://pubmed.ncbi.nlm.nih.gov/38341472/

2. Garbincius, Joanne F, Salik, Oniel, Cohen, Henry M, Tomar, Dhanendra, Elrod, John W. 2023. TMEM65 regulates NCLX-dependent mitochondrial calcium efflux. In bioRxiv : the preprint server for biology, , . doi:10.1101/2023.10.06.561062. https://pubmed.ncbi.nlm.nih.gov/37873405/

3. Teng, Allen C T, Gu, Liyang, Di Paola, Michelle, Hamilton, Robert M, Gramolini, Anthony O. 2022. Tmem65 is critical for the structure and function of the intercalated discs in mouse hearts. In Nature communications, 13, 6166. doi:10.1038/s41467-022-33303-y. https://pubmed.ncbi.nlm.nih.gov/36257954/

4. Garbincius, Joanne F, Salik, Oniel, Cohen, Henry M, Tomar, Dhanendra, Elrod, John W. 2025. TMEM65 regulates and is required for NCLX-dependent mitochondrial calcium efflux. In Nature metabolism, 7, 714-729. doi:10.1038/s42255-025-01250-9. https://pubmed.ncbi.nlm.nih.gov/40200126/

5. Nishimura, Naotaka, Gotoh, Tomomi, Oike, Yuichi, Yano, Masato. 2014. TMEM65 is a mitochondrial inner-membrane protein. In PeerJ, 2, e349. doi:10.7717/peerj.349. https://pubmed.ncbi.nlm.nih.gov/24765583/

6. Urushima, Yuto, Haraguchi, Misa, Yano, Masato. 2020. Depletion of TMEM65 leads to oxidative stress, apoptosis, induction of mitochondrial unfolded protein response, and upregulation of mitochondrial protein import receptor TOMM22. In Biochemistry and biophysics reports, 24, 100870. doi:10.1016/j.bbrep.2020.100870. https://pubmed.ncbi.nlm.nih.gov/33319071/