The loss-of-function PCSK9Q152H variant increases ER chaperones GRP78 and GRP94 and protects against liver injury
Paul F. Lebeau, Hanny Wassef, Jae Hyun Byun, Khrystyna Platko, Brandon Ason, Simon Jackson, Joshua Dobroff, Susan Shetterly, William G. Richards, Ali A. Al-Hashimi, Kevin Doyoon Won, Majambu Mbikay, Annik Prat, An Tang, Guillaume Paré, Renata Pasqualini, Nabil G. Seidah, Wadih Arap, Michel Chrétien, Richard C. Austin
Paul F. Lebeau, Hanny Wassef, Jae Hyun Byun, Khrystyna Platko, Brandon Ason, Simon Jackson, Joshua Dobroff, Susan Shetterly, William G. Richards, Ali A. Al-Hashimi, Kevin Doyoon Won, Majambu Mbikay, Annik Prat, An Tang, Guillaume Paré, Renata Pasqualini, Nabil G. Seidah, Wadih Arap, Michel Chrétien, Richard C. Austin
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Research Article Hepatology Vascular biology

The loss-of-function PCSK9Q152H variant increases ER chaperones GRP78 and GRP94 and protects against liver injury

Abstract

Individuals harboring the loss-of-function (LOF) proprotein convertase subtilisin/kexin type 9 Gln152His variation (PCSK9Q152H) have low circulating low-density lipoprotein cholesterol levels and are therefore protected against cardiovascular disease (CVD). This uncleavable form of proPCSK9, however, is retained in the endoplasmic reticulum (ER) of liver hepatocytes, where it would be expected to contribute to ER storage disease (ERSD), a heritable condition known to cause systemic ER stress and liver injury. Here, we examined liver function in members of several French-Canadian families known to carry the PCSK9Q152H variation. We report that PCSK9Q152H carriers exhibited marked hypocholesterolemia and normal liver function despite their lifelong state of ER PCSK9 retention. Mechanistically, hepatic overexpression of PCSK9Q152H using adeno-associated viruses in male mice greatly increased the stability of key ER stress-response chaperones in liver hepatocytes and unexpectedly protected against ER stress and liver injury rather than inducing them. Our findings show that ER retention of PCSK9 not only reduced CVD risk in patients but may also protect against ERSD and other ER stress–driven conditions of the liver. In summary, we have uncovered a cochaperone function for PCSK9Q152H that explains its hepatoprotective effects and generated a translational mouse model for further mechanistic insights into this clinically relevant LOF PCSK9 variant.

Authors

Paul F. Lebeau, Hanny Wassef, Jae Hyun Byun, Khrystyna Platko, Brandon Ason, Simon Jackson, Joshua Dobroff, Susan Shetterly, William G. Richards, Ali A. Al-Hashimi, Kevin Doyoon Won, Majambu Mbikay, Annik Prat, An Tang, Guillaume Paré, Renata Pasqualini, Nabil G. Seidah, Wadih Arap, Michel Chrétien, Richard C. Austin

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Figure 3

Characterization of PCSK9/LDLR AAV–treated mice.

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Characterization of PCSK9/LDLR AAV–treated mice. Pcsk9–/– mice (n = 5) w...
Pcsk9–/– mice (n = 5) were treated with AAV encoding empty vector (EV), human (h) PCSK9 WT, or ER-retained variants hPCSK9Q152H and hLDLRG544V. (A and B) Intracellular PCSK9 expression and retention were assessed via IHC staining and quantification using ImageJ software. (C) Immunofluorescent staining of PCSK9 and the ER marker protein disulfide isomerase (PDI) was also used to visualize ER PCSK9 retention and expansion (ER area depicted as yellow dotted line). (D and E) Secreted PCSK9 levels were examined using human (D) and mouse (E) PCSK9 ELISAs. (F) Liver expression of immature LDLR (LDLR-i; 100 kDa) and proPCSK9 (75 kDa) was confirmed via immunoblots. (G–J) Additional parameters known to be modulated by secreted PCSK9, including cell surface hepatic LDLR expression (G and H), plasma triglyceride levels (I), and plasma cholesterol levels (J), were also examined. Values are represented as mean ± SD. *P < 0.05. ANOVA was used for all statistical comparisons (A–J). Scale bars: A and G, 200 μm; C, 10 μm. Original magnification, ×60 (A, lower panels).