Optineurin associates with the podocyte Golgi complex to maintain its structure.

Optineurin, a cytosolic protein associated with the actin cytoskeleton, microtubules, and the Golgi complex, appears to have an important function in neurons, as mutations in its gene are causative for neurodegenerative diseases such as primary open-angle glaucoma and amyotrophic lateral sclerosis. Here, we report that optineurin is localized in podocytes of the kidney and induced upon injury following treatment with puromycin aminonucleoside. In cultured human podocytes, optineurin localizes to the Golgi complex. Optineurin depletion by RNA interference causes Golgi fragmentation. Moreover, if the Golgi complex is fragmented following microtubule destabilization induced by nocodazole treatment, optineurin dissociates from Golgi vesicles. Furthermore, optineurin colocalizes with vinculin-labeled focal contacts of cultured podocytes and with lysosome-like structures. Optineurin is essential for the survival of cultured podocytes, as optineurin depletion causes cell death. Thus, optineurin appears to play an important role in the maintenance of the podocyte Golgi complex and in the trafficking of vesicles to focal contacts and lysosomes.

Depletion of optineurin in RGC-5 cells derived from retinal neurons causes apoptosis and reduces the secretion of neurotrophins.

Optineurin is a Golgi complex-associated ubiquitous protein with high expression levels in retinal ganglion cells (RGCs). Mutations in optineurin have been observed in rare hereditary cases of primary open-angle glaucoma and in amyotrophic lateral sclerosis. We explored the possibility that optineurin deficiency will compromise neuronal exocytosis leading to a diminished secretion of neurotrophic factors that are critically required for neuronal survival. To this end, we used RNA interference to induce depletion of optineurin in RGC-5 cells derived from retinal neurons. SiRNA specific for optineurin was transiently transfected. Moreover, a stable cell line with constitutive optineurin deficiency (RGC-5 pSilencer OPTN) was generated. In addition, we investigated the subcellular localization of optineurin in primary RGCs in retinal cell cultures isolated from eyes of mature mice. In RGC-5 cells, optineurin localized to the periphery of the Golgi complex and was observed in vesicular structures throughout the cytoplasm and close to the plasma membrane. A comparable Golgi-associated localization of optineurin was observed in cultured primary RGCs that were identified by TUJ1 labeling. Optineurin deficiency caused a marked increase in the number of RGC-5 cells with fragmented Golgi complex. RGC-5 pSilencer OPTN with stable optineurin deficiency showed a pronounced increase in the number of cells undergoing apoptotic cell death. Furthermore, the amounts of secreted neurotrophin-3 (NT-3) and ciliary neurotrophic factor were significantly lower in culture medium of RGC-5 pSilencer OPTN cells when compared to controls. Adding exogenous NT-3 to the culture medium to achieve amounts seen in control cultures completely prevented the increase in apoptotic cell death. We propose that lack of neurotrophic support due to impaired secretion of neurotrophic proteins is a critical factor that causes or contributes to RGC or motor neuron death in patients with mutated optineurin.