Abstract
Purpose :
Age is a major risk factor for many retinal diseases which, together, are estimated to severely impact on the visual function of >1.8 billion people by 2050. The precise pathobiology underpinning age-associated retinal degeneration remains ill-defined although there is broad recognition that low-grade chronic inflammation plays an important role. Regulatory T cells (Treg) have recently emerged as key players in tissue homeostasis, due to their capacity to regulate local immune responses and limit inflammation, as well as their role in metabolic regulation, regeneration, and neuroprotection. However, the role of Treg in retinal homeostasis and age-associated retinal neurodegeneration is yet to be investigated.
Methods :
Treg depletion was induced by intraperitoneal diphtheria toxin (DT) administration to Foxp3-DTR mice over 17 days (3 consecutive DT injections and then one DT injection every 4 days). The retinal neurovascular unit was assessed in young (3-4m) and aged (16-23m) Foxp3-DTR mice receiving DT, its vehicle (PBS) and C57BL/6 WT mice receiving DT. Gliosis (GFAP, Iba-1, CD68) and changes in neuronal populations (PKCα/secretagogin, rod/cone bipolar cells; Brn3a, retinal ganglion cells; Cone-arrestin, cone-photoreceptors) were assessed by immunohistochemistry.
Results :
We observed a significant decrease Cone-arrestin+ and DAPI+ cells in the ONL in Treg-depleted aged but not young Foxp3-DTR mice, along with an alteration in the typical laminarity of cone and rod bipolar cells in the INL, further indicating retinal neurodegeneration. Aged Foxp3-DTR mice treated with DT also showed enhanced Müller cell gliosis, especially in the ONL. Interestingly, an increase in Iba-1+ cells was found in the ONL of aged Foxp3-DTR treated with DT as well as in the subretinal space of both aged and young Foxp3-DTR, together with RPE dysmorphology. Considering the differences observed between young and aged Treg-depleted mice, we analysed changes in expression in between young and aged Treg. When compared with young Treg, aged Treg showed an upregulation of genes linked to gene ontology terms related to neuronal processes, suggesting that with aging Treg may acquire a neuroprotective role.
Conclusions :
Depletion of Foxp3+ Tregs exacerbates retinal neurodegeneration, Muller gliosis and microglia infiltration in aged animals compared to young controls. Hence, Treg have a key role in regulating immune homeostasis in age-related retinal pathology.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.