TMEM135, a transmembrane protein, is thought to regulate the balance between mitochondrial fusion and fission, and is involved in lipid droplet formation/tethering, fatty acid metabolism, and peroxisomal function [3]. It participates in multiple biological pathways related to energy metabolism, cell differentiation, and organelle function, thus being of great biological importance. Genetic models, especially KO mouse models, have been crucial in studying its functions.

In adipose tissue, adipose-specific TMEM135 knockout in mice blocks mitochondrial fission, impairs thermogenesis, and increases diet-induced obesity and insulin resistance. Conversely, its overexpression promotes mitochondrial division, counteracts obesity and insulin resistance, and rescues thermogenesis in peroxisome-deficient mice [1]. In bone marrow mesenchymal stem cells (BMSCs), Tmem135 knockout mice show an osteoporotic phenotype with reduced osteogenesis and increased adipogenesis due to impaired mitochondrial fission and disrupted energy metabolism during osteogenesis [2]. In the inner ear, a mutation in Tmem135 (FUN025) causes progressive sensorineural hearing loss in mice, accompanied by a severe loss of outer hair cells and spiral ganglion neurons in the cochlea [4,7]. In the liver, TMEM135 deficiency mitigates lipid accumulation in high-fat diet-fed mice by suppressing CD36 in a SIRT1-dependent manner, improving hepatic steatosis [5]. In the retina, overexpression and mutation of Tmem135 cause contrasting retinal pigmented epithelium (RPE) abnormalities in mice, correlating with changes in mitochondrial shape and size, suggesting its importance in RPE health [6].

In conclusion, TMEM135 plays essential roles in maintaining mitochondrial dynamics, energy homeostasis, and cell differentiation in various tissues. The KO/CKO mouse models have revealed its significance in diseases such as obesity, insulin resistance, osteoporosis, sensorineural hearing loss, hepatic steatosis, and retinal pathologies. These findings provide potential therapeutic targets for treating related diseases by targeting TMEM135.

References:

1. Hu, Donghua, Tan, Min, Lu, Dongliang, Ikeda, Akihiro, Lodhi, Irfan J. 2023. TMEM135 links peroxisomes to the regulation of brown fat mitochondrial fission and energy homeostasis. In Nature communications, 14, 6099. doi:10.1038/s41467-023-41849-8. https://pubmed.ncbi.nlm.nih.gov/37773161/

2. Liu, Jia, Bao, Xiaogang, Huang, Jian, Shi, Changgui, Xu, Guohua. 2023. TMEM135 maintains the equilibrium of osteogenesis and adipogenesis by regulating mitochondrial dynamics. In Metabolism: clinical and experimental, 152, 155767. doi:10.1016/j.metabol.2023.155767. https://pubmed.ncbi.nlm.nih.gov/38154611/

3. Beasley, Heather K, Rodman, Taylor A, Collins, Greg V, Hinton, Antentor, Exil, Vernat. 2021. TMEM135 is a Novel Regulator of Mitochondrial Dynamics and Physiology with Implications for Human Health Conditions. In Cells, 10, . doi:10.3390/cells10071750. https://pubmed.ncbi.nlm.nih.gov/34359920/

4. Kim, Mi-Jung, Simms, Shion, Behnammanesh, Ghazaleh, Ikeda, Akihiro, Someya, Shinichi. 2024. A Mutation in Tmem135 Causes Progressive Sensorineural Hearing Loss. In bioRxiv : the preprint server for biology, , . doi:10.1101/2024.05.09.593414. https://pubmed.ncbi.nlm.nih.gov/38766120/

5. Chhetri, Arun, Park, Channy, Kim, Hyunsoo, Lee, Sang-Wook, Park, Raekil. 2024. TMEM135 deficiency improves hepatic steatosis by suppressing CD36 in a SIRT1-dependent manner. In Molecular metabolism, 92, 102080. doi:10.1016/j.molmet.2024.102080. https://pubmed.ncbi.nlm.nih.gov/39647810/

6. Landowski, Michael, Grindel, Samuel, Shahi, Pawan K, Pattnaik, Bikash R, Ikeda, Akihiro. . Modulation of Tmem135 Leads to Retinal Pigmented Epithelium Pathologies in Mice. In Investigative ophthalmology & visual science, 61, 16. doi:10.1167/iovs.61.12.16. https://pubmed.ncbi.nlm.nih.gov/33064130/

7. Kim, Mi-Jung, Simms, Shion, Behnammanesh, Ghazaleh, Ikeda, Akihiro, Someya, Shinichi. 2025. A mutation in Tmem135 causes progressive sensorineural hearing loss. In Hearing research, 459, 109221. doi:10.1016/j.heares.2025.109221. https://pubmed.ncbi.nlm.nih.gov/39970612/