Is Lipoprotein(a) Clinically Actionable with Today's Evidence? The Answer is Yes.

PURPOSE OF REVIEW: Lipoprotein(a) is an independent risk factor for cardiovascular disease. We review the ongoing shifts in consensus guidelines for the testing and management of Lp(a) and provide insight into whether current evidence suggests that awareness and testing of Lp(a) is clinically actionable. RECENT FINDINGS: GWAS and Mendelian randomization studies have established causal links between elevated Lp(a) and forms of CVD, including CAD and calcific aortic valve disease. Testing of Lp(a) identifies patients with similar risk to that of heterozygous FH, enhances risk stratification in patients with borderline/intermediate risk as determined through traditional factors, and facilitates the assessment of inherited CVD risk through cascade screening in patients with known family history of elevated Lp(a). Reductions in Lp(a) through non-targeted therapies including PCSK9 inhibition and lipoprotein apheresis have demonstrated reductions in ASCVD risk that are likely attributable to lowering Lp(a). Targeted therapies to potently lower Lp(a) are in clinical development. Lp(a) is actionable, and can be used to identify high risk patients for primary prevention and their family members through cascade screening, and to guide intensification of therapy in primary and secondary prevention of ASCVD.

Trends in testing and prevalence of elevated Lp(a) among patients with aortic valve stenosis.

BACKGROUND AND AIMS: Lipoprotein(a) [Lp(a)] is causally associated with aortic valve stenosis (AS) but Lp(a) testing among AS patients is not broadly incorporated into clinical practice. We evaluated trends in Lp(a) testing in an academic medical center. METHODS: Educational efforts and adding Lp(a) to the lipid panel on the electronic medical record (EMR) and pre-procedure order sets were used to increase awareness of Lp(a) as a risk factor in AS. Medical records at University of California San Diego Health (UCSDH) were analyzed from 2010 to 2020 to define the yearly frequency of first time Lp(a) testing in patients with diagnosis codes for AS or undergoing transcatheter aortic valve replacement (TAVR). RESULTS: Lp(a) testing for any indication increased over 5-fold from 2010 to 2020. A total of 3808 patients had a diagnosis of AS and 417 patients had TAVR. Lp(a) levels >30 mg/dL were present in 37% of AS and 35% of TAVR patients. The rates of Lp(a) testing in AS and TAVR were 14.0% and 65.7%, respectively. In AS, Lp(a) testing increased over time from 8.5% in 2010, peaking at 24.2% in 2017, and declining to 13.9% in 2020 (p < 0.001 for trend). Following implementation of EMR order-sets in 2016, Lp(a) testing in TAVR cases increased to a peak of 88.5% in 2018. CONCLUSIONS: Elevated Lp(a) is prevalent in AS and TAVR patients. Implementation of educational efforts and practice pathways resulted in increased Lp(a) testing in patients with AS. This study represents a paradigm that may allow increased global awareness of Lp(a) as a risk factor for AS.

Myocardial Strain and Association With Clinical Outcomes in Danon Disease: A Model for Monitoring Progression of Genetic Cardiomyopathies.

Background Myocardial strain can identify subclinical left ventricular dysfunction in various cardiac diseases, but its association with clinical outcomes in genetic cardiomyopathies remains unknown. Herein, we assessed myocardial strain in patients with Danon disease (DD), a rare X-linked autophagic disorder that causes severe cardiac manifestations. Methods and Results Echocardiographic images were reviewed and used to calculate myocardial strain from a retrospective, international registry of patients with DD. Regression analyses were performed to evaluate for an association of global longitudinal strain (GLS) and ejection fraction with the composite outcome (death, ventricular assist device, heart transplantation, and implantable cardioverter defibrillator for secondary prevention). A total of 22 patients with DD (male 14 [63.6%], median age 16.5 years) had sufficient echocardiograms for analysis. Absolute GLS was reduced with a mean of 12.2% with an apical-sparing pattern observed. Univariable regression for GLS and composite outcome showed an odds ratio of 1.32 (95% CI, 1.02-1.71) with P=0.03. For receiver operating characteristic analysis, the areas under the curve for GLS and ejection fraction were 0.810 (P=0.02) and 0.605 (P=0.44), respectively. An absolute GLS cutoff of 10.0% yielded a true positive rate of 85.7% and false positive rate of 13.3%. Conclusions In this cohort of patients with DD, GLS may be a useful assessment of myocardial function and may predict clinical outcomes. This study highlights the potential use of myocardial strain phenotyping to monitor disease progression and potentially to predict clinical outcomes in DD and other genetic cardiomyopathies.

Lipoprotein(a) in Patients Undergoing Transcatheter Aortic Valve Replacement.

Lipoprotein(a) [Lp(a)] is a genetically determined risk factor for calcific aortic valve stenosis (CAVS) for which transcatheter aortic valve replacement (TAVR) is increasingly utilized as treatment. We evaluated the effect of a program to increase testing of and define the prevalence of elevated Lp(a) among patients undergoing TAVR. Educational efforts and incorporation of a "check-box" Lp(a) order to the preoperative TAVR order set were instituted. Retrospective chart review was performed in 229 patients requiring TAVR between May 2013 and September 2018. Of these patients, 57% had an Lp(a) level measured; testing rates increased from 0% in 2013 to 96% in 2018. Lipoprotein(a) testing occurred in 11% of patients before and in 80% of patients after the "check-box" order set ( P < .001). The prevalence of elevated Lp(a) (≥30 mg/dL) was 35%; these patients had a higher incidence of coronary artery disease requiring revascularization compared with patients with normal Lp(a) (65% vs 47%; P = .047). Patients with Lp(a) ≥30 mg/dL also had higher incidence of paravalvular leak compared with those with normal Lp(a) (13% vs 4%; P = .04). This study defines the prevalence of elevated Lp(a) in advanced stages of CAVS and provides a practice pathway to assess procedural complications and long-term outcomes of TAVR in patients with elevated Lp(a) levels.

The Prevalence of Lipoprotein(a) Measurement and Degree of Elevation Among 2710 Patients With Calcific Aortic Valve Stenosis in an Academic Echocardiography Laboratory Setting.

Lipoprotein(a; Lp[a]) and its associated oxidized phospholipids are causal, genetic risk factors for calcific aortic valve stenosis (CAVS). We determined the prevalence of Lp(a) measurement among 2710 patients with CAVS and 1369 control patients (∼50% of study group) without CAVS with an echocardiogram between January 2010 and February 2016 in an academic echocardiography laboratory. Lipoprotein(a) measurements were performed at a referral laboratory using an isoform-independent assay. The prevalence of any Lp(a) measurement was 4.6% (124 of the 2710) in patients with CAVS and 3.1% (42 of the 1369) in the control group ( P = .021). In patients with CAVS, mean (standard deviation) Lp(a) levels were 38 (54) mg/dL and median (interquartile range) Lp(a) levels were 14 (6-48) mg/dL. Of the 124 patients with CAVS having Lp(a) measurements, 83 (66.9%) had Lp(a) <30 mg/dL and 41 (33.1%) had Lp(a) ≥30 mg/dL. This study reflects low physician testing of Lp(a) levels in CAVS. Given the role of Lp(a) as a causal risk factor for CAVS, and the ongoing development of therapies to normalize Lp(a) levels, our results suggest that Lp(a) measurements in CAVS should be more widely obtained in clinical practice.

GIV/girdin binds exocyst subunit-Exo70 and regulates exocytosis of GLUT4 storage vesicles.

Insulin resistance (IR) is a metabolic disorder characterized by impaired glucose uptake in response to insulin. The current paradigm for insulin signaling centers upon the insulin receptor (InsR) and its substrate IRS1; the latter is believed to be the chief conduit for post-receptor signaling. We recently demonstrated that GIV, a Guanidine Exchange Factor (GEF) for the trimeric G protein, Gαi, is a major hierarchical conduit for the metabolic insulin response. By virtue of its ability to directly bind the InsR, IRS1 and PI3K, GIV enhances the InsR-IRS1-Akt-AS160 (RabGAP) signaling cascade and cellular glucose uptake via its GEF function. Phosphoinhibition of GIV-GEF by the fatty-acid/PKCθ pathway inhibits the cascade and impairs glucose uptake. Here we show that GIV directly and constitutively binds the exocyst complex subunit Exo-70 and also associates with GLUT4-storage vesicles (GSVs) exclusively upon insulin stimulation. Without GIV or its GEF function, membrane association of Exo-70 as well as exocytosis of GSVs in response to insulin are impaired. Thus, GIV is an essential component within the insulin signaling cascade that couples upstream signal transducers within the InsR and G-Protein signaling cascade to downstream vesicular trafficking events within the exocytic pathway. These findings suggest a role of GIV in coordinating key signaling and trafficking events of metabolic insulin response.

Activation of G proteins by GIV-GEF is a pivot point for insulin resistance and sensitivity.

Insulin resistance (IR) is a metabolic disorder characterized by impaired insulin signaling and cellular glucose uptake. The current paradigm for insulin signaling centers upon the insulin receptor (InsR) and its substrate IRS1; the latter is believed to be the sole conduit for postreceptor signaling. Here we challenge that paradigm and show that GIV/Girdin, a guanidine exchange factor (GEF) for the trimeric G protein Gαi, is another major hierarchical conduit for the metabolic insulin response. By virtue of its ability to directly bind InsR, IRS1, and phosphoinositide 3-kinase, GIV serves as a key hub in the immediate postreceptor level, which coordinately enhances the metabolic insulin response and glucose uptake in myotubes via its GEF function. Site-directed mutagenesis or phosphoinhibition of GIV-GEF by the fatty acid/protein kinase C-theta pathway triggers IR. Insulin sensitizers reverse phosphoinhibition of GIV and reinstate insulin sensitivity. We also provide evidence for such reversible regulation of GIV-GEF in skeletal muscles from patients with IR. Thus GIV is an essential upstream component that couples InsR to G-protein signaling to enhance the metabolic insulin response, and impairment of such coupling triggers IR. We also provide evidence that GIV-GEF serves as therapeutic target for exogenous manipulation of physiological insulin response and reversal of IR in skeletal muscles.

Therapeutic effects of cell-permeant peptides that activate G proteins downstream of growth factors.

In eukaryotes, receptor tyrosine kinases (RTKs) and trimeric G proteins are two major signaling hubs. Signal transduction via trimeric G proteins has long been believed to be triggered exclusively by G protein-coupled receptors (GPCRs). This paradigm has recently been challenged by several studies on a multimodular signal transducer, Gα-Interacting Vesicle associated protein (GIV/Girdin). We recently demonstrated that GIV's C terminus (CT) serves as a platform for dynamic association of ligand-activated RTKs with Gαi, and for noncanonical transactivation of G proteins. However, exogenous manipulation of this platform has remained beyond reach. Here we developed cell-permeable GIV-CT peptides by fusing a TAT-peptide transduction domain (TAT-PTD) to the minimal modular elements of GIV that are necessary and sufficient for activation of Gi downstream of RTKs, and used them to engineer signaling networks and alter cell behavior. In the presence of an intact GEF motif, TAT-GIV-CT peptides enhanced diverse processes in which GIV's GEF function has previously been implicated, e.g., 2D cell migration after scratch-wounding, invasion of cancer cells, and finally, myofibroblast activation and collagen production. Furthermore, topical application of TAT-GIV-CT peptides enhanced the complex, multireceptor-driven process of wound repair in mice in a GEF-dependent manner. Thus, TAT-GIV peptides provide a novel and versatile tool to manipulate Gαi activation downstream of growth factors in a diverse array of pathophysiologic conditions.

Multimodular biosensors reveal a novel platform for activation of G proteins by growth factor receptors.

Environmental cues are transmitted to the interior of the cell via a complex network of signaling hubs. Receptor tyrosine kinases (RTKs) and trimeric G proteins are two such major signaling hubs in eukaryotes. Conventionally, canonical signal transduction via trimeric G proteins is thought to be triggered exclusively by G protein-coupled receptors. Here we used molecular engineering to develop modular fluorescent biosensors that exploit the remarkable specificity of bimolecular recognition, i.e., of both G proteins and RTKs, and reveal the workings of a novel platform for activation of G proteins by RTKs in single living cells. Comprised of the unique modular makeup of guanidine exchange factor Gα-interacting vesicle-associated protein (GIV)/girdin, a guanidine exchange factor that links G proteins to a variety of RTKs, these biosensors provide direct evidence that RTK-GIV-Gαi ternary complexes are formed in living cells and that Gαi is transactivated within minutes after growth factor stimulation at the plasma membrane. Thus, GIV-derived biosensors provide a versatile strategy for visualizing, monitoring, and manipulating the dynamic association of Gαi with RTKs for noncanonical transactivation of G proteins in cells and illuminate a fundamental signaling event regulated by GIV during diverse cellular processes and pathophysiologic states.