Immune Cell Fat Switch: Losing RORα Worsens Blinding Eye Disease in Mice

Age-related macular degeneration, the leading cause of irreversible blindness in older adults, has long been linked to cholesterol and fat deposits in the back of the eye. Now a new mouse study published in the journal Angiogenesis reveals a surprising molecular culprit that ties those lipid deposits directly to the destructive inflammation behind the disease’s most devastating form. The research, led by Neetu Kushwah and Jing Chen of Boston Children’s Hospital and Harvard Medical School, identifies a fat-sensing nuclear receptor called RORα as a critical brake on both lipid overload and chronic inflammation in the retina, and shows that losing it dramatically worsens the pathological blood vessel growth that defines wet AMD.

RORα, short for retinoic acid receptor-related orphan receptor alpha, is a transcription factor that senses cholesterol levels and switches genes on or off in response. Genetic variants of the RORA gene have previously been associated with increased susceptibility to both the dry and neovascular forms of AMD in humans, and earlier work from the same group showed that RORα deficiency worsens laser-induced choroidal neovascularization in young mice. What remained unclear was exactly how the receptor influences the immune cells that swarm into the aging retina and whether its effects on fat metabolism and inflammation were two sides of the same coin. The new study set out to answer that question using two complementary mouse models: the spontaneous Staggerer mutant (Rora sg/sg), which lacks functional RORα throughout the body, and a myeloid-specific knockout (Rora fl/fl;LysMCre) in which the receptor is deleted only in macrophages and related immune cells.

The results were striking. As the Staggerer mice aged, they developed increasing numbers of abnormal whitish-yellow fundus lesions that resemble the drusen and deposits seen in human AMD patients, with more than a fivefold increase in lesion number by nine months of age. Retinal cross-sections revealed subretinal deposits, focal disruption of the retinal pigment epithelium, and sloughed RPE cells. Critically, the subretinal space of these mice, which in healthy eyes is normally kept free of immune cells by immunosuppressive factors secreted by the RPE, became crowded with CD11b- and IBA1-positive microglia and macrophages. The counts were more than double those of age-matched controls, and the accumulated immune cells were visibly bloated with neutral lipids, stained with a fluorescent lipid probe called LipidSpot 610. The number of these lipid-laden cells correlated with the density of fundus lesions, suggesting a causal relationship between immune cell fat overload and the visible pathology.

When the researchers induced choroidal neovascularization with laser photocoagulation in aged mice, the Staggerer animals fared far worse than controls. Their CNV lesions were significantly larger, surrounded by expanded zones of IBA1-positive macrophages and microglia, and far leakier on fluorescein angiography. While roughly 43 percent of lesions in wild-type aged mice showed only mild grade 1 hyperfluorescence and none reached the pathologically significant grade 2B, the RORα-deficient mice showed a much higher proportion of severely leaking lesions. Even outside the laser sites, the microglia of deficient mice displayed an activated, amoeboid morphology, with enlarged cell bodies, fewer branches, and shorter processes, the classic signature of inflammatory rather than surveillance-mode immune cells.

To prove that these effects stemmed from the immune cells themselves rather than some other tissue, the team turned to the myeloid-specific knockout. Deleting RORα only in the myeloid lineage reproduced the key findings: more fundus lesions at six, twelve, and beyond twelve months of age, larger lesion areas, increased subretinal accumulation of activated microglia, and elevated lipid droplet formation in immune cells of both young and aged animals. Laser-induced CNV lesions were larger in these mice as well, with 84 percent graded as leaky compared with 41 percent in floxed controls, and ex vivo choroidal explants from the knockout mice sprouted significantly more vessels, pointing to a pro-angiogenic shift driven by macrophages rather than by the vascular endothelium directly.

The mechanistic heart of the paper lies in what RORα does to PPARγ, a master regulator of fat uptake and storage. In RORα-deficient macrophages, retinas, and RPE/choroid tissue, Pparg mRNA and PPARγ protein were substantially upregulated, roughly doubling at the protein level. Chromatin immunoprecipitation experiments showed that RORα physically binds to a specific response element in the Pparg promoter, indicating that under normal conditions the receptor directly represses this lipogenic gene. When RORα is absent or pharmacologically inhibited with inverse agonists such as SR3335 and SR1001, PPARγ expression surges, lipid droplet formation increases roughly threefold, and macrophages take up more low-density lipoprotein. Exposure to 7-ketocholesterol, an oxidized cholesterol product that is a major component of drusen, further exaggerated lipid accumulation in the deficient cells, highlighting their heightened vulnerability to the very molecules that pile up in AMD eyes.

The lipid overload was not benign. RORα-deficient macrophages, retinas, and RPE/choroid samples showed elevated levels of the pro-inflammatory cytokines TNFα, IL-6, and IL-1β, along with reduced anti-inflammatory IL-10, and increased activation of NF-κB, the central inflammatory signaling pathway implicated in AMD. The deficient immune cells also lost expression of two migratory receptors, CX3CR1 and CD47, which are essential for macrophages and microglia to exit the subretinal space once their cleanup work is done. CD47 in particular is a known AMD risk factor that declines with age in humans. With these exit routes downregulated, the cells became trapped, proliferated more actively, migrated more aggressively in transwell assays, and produced more angiogenic factors including VEGF-A, VEGF-D, and angiopoietin-2. Conditioned medium from lipid-laden macrophages even stimulated the proliferation of human choroidal endothelial cells in culture, providing a direct functional link between macrophage fat overload and new blood vessel growth.

Perhaps most importantly for patients, the pathway proved druggable, at least in mice. When the researchers treated myeloid-specific knockout animals with T0070907, a selective PPARγ antagonist, before and during laser-induced CNV, lesion size shrank significantly, lipid droplet accumulation in retinal macrophages dropped markedly, and retinal expression of TNFα and IL-6 fell. This demonstrates that PPARγ acts as a key downstream effector of RORα signaling and that blocking it can partially reverse the damage caused by losing the receptor. In other words, the RORα–PPARγ axis offers a concrete therapeutic target: restoring RORα function or damping PPARγ activity could, in principle, restore lipid balance in retinal immune cells and cool the chronic inflammation that fuels neovascularization.

The findings arrive at a moment of growing translational momentum for RORα biology. A recent study showed that RORA-expressing gene therapy rescued retinal degeneration in a mouse model of Stargardt disease and dry AMD, and clinical trials evaluating RORA as a gene modifier therapy are currently underway for those conditions. The new work extends the receptor’s relevance to the wet, neovascular form of the disease and pinpoints the myeloid cell as the critical cellular mediator. There are caveats: the LysMCre system does not exclusively target microglia and shows incomplete recombination in that population, so the results reflect deletion in LysM-expressing myeloid cells broadly, and the human genetic association data for RORA and AMD risk have not been extensively updated by more recent studies. Still, the convergence of mouse genetics, pharmacology, chromatin biology, and human genetic association makes a compelling case that RORα sits at the junction of lipid metabolism and immune regulation in the aging retina.

What emerges is a coherent model of AMD pathogenesis in which a single nuclear receptor orchestrates an entire disease program. Under normal conditions, active RORα signaling keeps PPARγ in check, maintains lipid homeostasis in microglia and macrophages, supports the expression of migratory receptors that allow immune cells to leave the subretinal space, and restrains inflammatory cytokine production. When RORα is lost, whether through genetic variation, aging-related dysfunction, or the flood of oxidized cholesterol that characterizes the AMD eye, the system flips: PPARγ rises, immune cells gorge on lipids and become trapped, NF-κB-driven inflammation intensifies, and pro-angiogenic signals recruit the abnormal choroidal vessels that destroy central vision. If future therapies can reengage this axis in human patients, they may finally address one of the deepest roots of a disease that currently can only be managed, not prevented, at its immunometabolic source.

Subject of Research: Role of the nuclear receptor RORα in myeloid cell lipid metabolism, subretinal inflammation, and choroidal neovascularization in age-related macular degeneration

Article Title: Myeloid deficiency of RORα exacerbates lipid dysregulation and laser-induced choroidal neovascularization

Article References: Kushwah, N., Liu, C.-H., Bora, K., Maurya, M., Pavlovich, M. C., Fu, Z., Kamenecka, T. M., Sun, Y., Solt, L. A., & Chen, J. (2026). Myeloid deficiency of RORα exacerbates lipid dysregulation and laser-induced choroidal neovascularization. Angiogenesis, 29(4), Article 73. https://doi.org/10.1007/s10456-026-10092-2

Image Credits: AI Generated

DOI: 10.1007/s10456-026-10092-2

Keywords: RORα, age-related macular degeneration, choroidal neovascularization, macrophages, microglia, PPARγ, lipid accumulation, inflammation, nuclear receptor, retina, drusen, NF-κB