Lysosomal dysfunction of corneal fibroblasts underlies the pathogenesis of Granular Corneal Dystrophy Type 2 and can be rescued by TFEB

Abstract

Granular corneal dystrophy type 2 (GCD2) is the most common form of transforming growth factor β‐induced (TGFBI) gene‐linked corneal dystrophy and is pathologically characterized by the corneal deposition of mutant‐TGFBIp. The defective autophagic degradation of pathogenic mutant‐TGFBIp has been shown in GCD2; however, its exact mechanisms are unknown. To address this, we investigated lysosomal functions using corneal fibroblasts. Levels of cathepsins K and L (CTSK and CTSL) were significantly decreased in GCD2 cells, but of cathepsins B and D (CTSB and CTSD) did not change. The maturation of the pro‐enzymes to their active forms (CTSB, CTSK and CTSL) was inhibited in GCD2 cells. CTSL enzymes directly degraded both LC3 (autophagosomes marker) and mutant‐TGFBIp. Exogenous CTSL expression dramatically reduced mutant‐TGFBIp in GCD2 cells, but not TGFBIp in WT cells. An increased lysosomal pH and clustered lysosomal perinuclear position were found in GCD2 cells. Transcription factor EB (TFEB) levels were significantly reduced in GCD2 cells, compared to WT. Notably, exogenous TFEB expression improved mutant‐TGFBIp clearance and lysosomal abnormalities in GCD2 cells. Taken together, lysosomal dysfunction in the corneal fibroblasts underlies the pathogenesis of GCD2, and TFEB has a therapeutic potential in the treatment of GCD2.

Overactivation of hepatic mechanistic target of rapamycin kinase complex 1 (mTORC1) is associated with low transcriptional activity of transcription factor EB and lysosomal dysfunction in dairy cows with clinical ketosis

“…It has been reported that liverspecific TFEB knockout mice have lower numbers and activities of lysosomes (Chao et al, 2018b). However, activated TFEB can markedly increase the activities of lysosomal hydrolases, such as CTSD (Nnah et al, 2019;Choi et al, 2020). In the present study, the downregulation of TFEB abundance, nuclear localization, and lysosome-related molecules, as well as upregulated p-TFEB, suggested that the transcriptional activity of TFEB was decreased.…”

Exacerbation of Granular Corneal Dystrophy Type 2 After Small Incision Lenticule Extraction

“…Recent molecular studies showed that the features and function of the mitochondria, as well as cellular oxidative stress, were altered in cultured corneal fibroblasts expressing mutant TGFBIp. 17 , 18 Choi et al 19 , 20 demonstrated that TGFBIp causes a delay in autophagic clearance because of impaired lysosomal function in cultured GCD2 corneal fibroblasts. Based on these studies, we hypothesize that the phenotypic expression of the GCD2 Arg124His mutation might be modified by other influential genes.…”

Compound Heterozygous Mutations in TGFBI Cause a Severe Phenotype of Granular Corneal Dystrophy Type 2

“…Several studies have reported that homozygous GCD2 corneal broblasts showed more oxidative stress and impaired autophagy functions, resulting in a greater accumulation of TGFBIp in the corneal broblasts 24,25 . Further, intracellular TGFBIp is reportedly cleared out via lysosomes, and this function is impaired in cultured GCD2 corneal broblasts 26 . We suspected the double production of mutated TGFBIps from p.Arg124His allele and heterozygous mutation in opposite alleles to result in an intracellular TGFBIp status closer to that seen in GCD2 homozygotes than in heterozygotes.…”