RESUMO
A precondition for efficient proinsulin export from the endoplasmic reticulum (ER) is that proinsulin meets ER quality control folding requirements, including formation of the Cys(B19)-Cys(A20) "interchain" disulfide bond, facilitating formation of the Cys(B7)-Cys(A7) bridge. The third proinsulin disulfide, Cys(A6)-Cys(A11), is not required for anterograde trafficking, i.e., a "lose-A6/A11" mutant [Cys(A6), Cys(A11) both converted to Ser] is well secreted. Nevertheless, an unpaired Cys(A11) can participate in disulfide mispairings, causing ER retention of proinsulin. Among the many missense mutations causing the syndrome of Mutant INS gene-induced Diabetes of Youth (MIDY), all seem to exhibit perturbed proinsulin disulfide bond formation. Here, we have examined a series of seven MIDY mutants [including G(B8)V, Y(B26)C, L(A16)P, H(B5)D, V(B18)A, R(Cpep + 2)C, E(A4)K], six of which are essentially completely blocked in export from the ER in pancreatic ß-cells. Three of these mutants, however, must disrupt the Cys(A6)-Cys(A11) pairing to expose a critical unpaired cysteine thiol perturbation of proinsulin folding and ER export, because when introduced into the proinsulin lose-A6/A11 background, these mutants exhibit native-like disulfide bonding and improved trafficking. This maneuver also ameliorates dominant-negative blockade of export of co-expressed wild-type proinsulin. A growing molecular understanding of proinsulin misfolding may permit allele-specific pharmacological targeting for some MIDY mutants.
Assuntos
Diabetes Mellitus Tipo 2/metabolismo , Proinsulina/metabolismo , Adolescente , Células Cultivadas , Cisteína/genética , Cisteína/metabolismo , Diabetes Mellitus Tipo 2/genética , Dissulfetos/metabolismo , Retículo Endoplasmático/genética , Retículo Endoplasmático/metabolismo , Humanos , Insulina/genética , Insulina/metabolismo , Células Secretoras de Insulina/metabolismo , Mutação de Sentido Incorreto/genética , Proinsulina/genética , Dobramento de ProteínaRESUMO
PURPOSE: To describe a case of chronic pediatric retinal detachment with multiple macrocysts, its surgical management, and a review of the literature. METHODS: Case report with fundus photography and optical coherence tomography. RESULTS: We describe a case of an asymptomatic, 11-year-old boy with a chronic rhegmatogenous retinal detachment with multiple peripheral macrocysts. The patient had counting fingers visual acuity on presentation. The detachment was successfully surgically repaired with scleral buckling, subretinal fluid drainage, cryotherapy, and a SF6 tamponade. At the 12-month follow-up, the retina remained attached with improvement of visual acuity to 20/100 with resolution of the cysts. Optical coherence tomography revealed loss of macular ellipsoid zone. Genetic testing revealed a heterozygous dominant COL11A1 mutation. CONCLUSION: To the authors' knowledge, this is the first reported case of chronic retinal detachment presenting with multiple peripheral macrocysts in a pediatric patient with Stickler syndrome. More research is needed into the cause and significance of retinal macrocysts, particularly in the pediatric population.