Senolytics and the Glaucoma Niche: Clearing Old Cells for Longer-Life Signals

This audio article is from VisualFieldTest.com.Read the full article here: https://visualfieldtest.com/en/senolytics-and-the-glaucoma-niche-clearing-old-cells-for-longer-life-signalsTest your visual field online: https://visualfieldtest.comSupport the show so new episodes keep coming: https://www.buzzsprout.com/2563091/supportExcerpt:Introduction Glaucoma is an age-related eye disease in which high pressure in the eye (intraocular pressure, or IOP) damages retinal nerve cells and leads to vision loss. Aging is the single biggest risk factor for glaucoma, and new research suggests this may be because aging eyes accumulate senescent cells – cells that have permanently stopped dividing and secrete inflammatory signals. Cellular senescence is a normal response to damage or stress, but when these old cells build up they release a mix of molecules called the senescence-associated secretory phenotype (SASP). SASP factors include inflammatory cytokines (like interleukin-6), growth factors (like TGF-β) and enzymes that remodel tissue. In eye tissues such as the trabecular meshwork (TM) (the drainage canal that controls IOP) and the optic nerve head (ONH) (where retinal ganglion cell axons exit the eye), senescent cells and their SASP appear to drive chronic inflammation and scarring. For example, one recent review noted that both TM cells and retinal ganglion cells in aging eyes show markers of senescence, and clearing those old cells improved retinal ganglion cell survival in animal models () (). This article reviews the evidence that senescence contributes to glaucoma and explores how senolytic therapies – drugs that specifically kill senescent cells – might help protect the eye. Senescence in the Glaucoma Niche Trabecular Meshwork Senescence The trabecular meshwork (TM) is a sponge-like tissue that drains fluid from the eye. With normal aging, TM cell numbers gradually decline and the meshwork develops thick, stiff extracellular material. Histological studies show that older eyes have far fewer TM cells than young eyes, and this loss is much greater in glaucoma patients (). When TM cells die or senesce and are replaced by scar-like matrix, the drainage channel narrows and IOP rises (). In fact, Zhang et al. describe how an “absence of TM cells, followed by their replacement with extracellular matrix, leads to increased resistance to fluid outflow” (). This fits with clinical observations that the aging outflow pathway becomes fibrotic (for example, accumulation of type VI collagen is seen in glaucomatous TM) and raises IOP (). Laboratory studies of TM cells have identified classic features of senescence in aging or stressed cells: enlarged shape, cell-cycle arrest, and expression of markers like p16^INK4a. Importantly, senescent TM cells unleash pro-inflammatory SASP factors. For example, senescent TM cells have been shown to overproduce interleukin-6 (IL-6), IL-8 and chemokines (CCL2, CXCL3) (). These cytokines can recruit immune cells and drive fibrotic signaling (notably TGF-β is also part of the ocular SASP). Such chronic inflammation likely stiffens the TM. In short, aged and diseased TM tissue accumulates senescent cells that secrete fibrosis-inducing signals, contributing to outflow obstruction and elevated IOP () (). Optic Nerve Head and Retina Senescence Glaucoma also damages the optic nerve head (ONH) and retinal ganglion cells (RGCs) that send signals from the eye to the brain. Aging affects these tissues too. RGCs in older eyes show more oxidative damage and are less able to survive stress (). Senescent cells in the retina (neurons or retinal support cells) similarly secrete SASP factors that can harm Support the show