AAV vectors expressing LDLR gain-of-function variants demonstrate increased efficacy in mouse models of familial hypercholesterolemia

S Somanathan, F Jacobs, Q Wang, AL Hanlon… - Circulation …, 2014 - Am Heart Assoc
S Somanathan, F Jacobs, Q Wang, AL Hanlon, JM Wilson, DJ Rader
Circulation research, 2014Am Heart Assoc
Rationale: Familial hypercholesterolemia is a genetic disorder that arises because of loss-of-
function mutations in the low-density lipoprotein receptor (LDLR) and homozygous familial
hypercholesterolemia is a candidate for gene therapy using adeno-associated viral vectors.
Proprotein convertase subtilisin/kexin type 9 (PCSK9) and inducible degrader of LDLR
(IDOL) negatively regulate LDLR protein and could dampen adeno-associated viral vector
encoded LDLR expression. Objective: We sought to create vectors expressing gain-of …
Rationale:
Familial hypercholesterolemia is a genetic disorder that arises because of loss-of-function mutations in the low-density lipoprotein receptor (LDLR) and homozygous familial hypercholesterolemia is a candidate for gene therapy using adeno-associated viral vectors. Proprotein convertase subtilisin/kexin type 9 (PCSK9) and inducible degrader of LDLR (IDOL) negatively regulate LDLR protein and could dampen adeno-associated viral vector encoded LDLR expression.
Objective:
We sought to create vectors expressing gain-of-function human LDLR variants that are resistant to degradation by human PCSK9 (hPCSK9) and IDOL and thereby enhance hepatic LDLR protein abundance and plasma LDL cholesterol reduction.
Methods and Results:
Amino acid substitutions were introduced into the coding sequence of human LDLR cDNA to reduce interaction with hPCSK9 and human IDOL. A panel of mutant human LDLRs was initially screened in vitro for escape from PCSK9. The variant human LDLR-L318D was further evaluated using a mouse model of homozygous familial hypercholesterolemia lacking endogenous LDLR and apolipoprotein B mRNA editing enzyme catalytic, APOBEC-1 (double knockout). Administration of wild-type human LDLR to double knockout mice, expressing hPCSK9, led to diminished LDLR activity. However, LDLR-L318D was resistant to hPCSK9-mediated degradation and effectively reduced cholesterol levels. Similarly, the LDLR-K809R\C818A construct avoided human IDOL regulation and achieved stable reductions in serum cholesterol. An adeno-associated viral vector serotype 8.LDLR-L318D\K809R\C818A vector that carried all 3 amino acid substitutions conferred partial resistance to both hPCSK9- and human IDOL–mediated degradation.
Conclusions:
Amino acid substitutions in the human LDLR confer partial resistance to PCSK9 and IDOL regulatory pathways with improved reduction in cholesterol levels and improve on a potential gene therapeutic approach to treat homozygous familial hypercholesterolemia subjects.
Am Heart Assoc