Ronald M. Krauss

Introduction: Genetic variants within the APOE-TOMM40 locus are associated with Alzheimer’s disease (AD). A specific role for TOMM40 is indicated by the finding that ‘523’ poly-T variants are associated with AD risk, but the mechanism for this effect has not been established. Our studies have shown that suppression of Tomm40 in mice increased brain cholesterol content, an AD risk factor, and thus the present study sought to assess whether major ‘523’ poly-T variants (Short [S] and Very Long [VL]) are associated with altered lipid content of brain and other tissues. Methods: We utilized a mouse model containing the entire human APOE3-TOMM40 locus to quantify cholesterol and triglyceride levels in brain, liver, and white adipose tissue (WAT), as well as brain content of the AD biomarkers Aβ 42 and tau, in mice carrying two homozygous TOMM40 ‘523’ poly-T genotypes (S/S and VL/VL). Results: Male mice carrying the ‘523’-S/S genotype, but not females, showed higher brain cholesterol and triglyceride levels than VL/VL carriers, together with greater brain Aβ 42 content. WAT showed similar lipid differences as in the brain, while hepatic lipid content was broadly similar between ‘523’-S/S and -VL/VL genotypes, though there was a trend for higher triglycerides in VL/VL mice in a sex- and age-dependent manner. Discussion: These results demonstrate that TOMM40 ‘523’ poly-T variants drive tissue-specific, sex-, and age-dependent lipid differences in humanized APOE3-TOMM40 mice, with the S/S genotype linked to elevated brain cholesterol and Aβ 42 levels, effects that link this locus to AD pathogenesis.

INTRODUCTION: While the apolipoprotein E ( APOE ) ε4 allele is a major risk factor for Alzheimer's disease (AD), the role of translocase of outer mitochondrial membrane 40 ( TOMM40 )—an adjacent gene involved in mitochondrial protein import—is not known. METHODS: Human brain tissue, human induced pluripotent stem cell–derived neurons (iNeurons), and mice were used for study of gene expression, cholesterol metabolism, mitochondrial function, and animal cognition. RESULTS: Human brain transcriptomics showed reduced TOMM40 expression that correlated with cholesterol regulatory gene expression, amyloid burden, and clinical AD diagnosis. In human iNeurons, TOMM40 knockdown (KD) disrupted mitochondria–endoplasmic reticulum contact sites (MERCs), causing mitochondrial dysfunction and promoting reactive oxygen species that led to activation of liver X receptor beta (NR1H2), upregulation of APOE and low‐density lipoprotein receptor ( LDLR ), and increased cellular cholesterol and amyloid beta (Aβ)42 independent of APOE ε4. Consistently, Tomm40 KD in mice induced increased brain cholesterol, Aβ42 content, and impaired memory. DISCUSSION: TOMM40 is a novel mediator of AD pathology through dual effects on MERCs that regulate cholesterol homeostasis and mitochondrial function.

Statins are the drugs most commonly used for lowering plasma low-density lipoprotein (LDL) cholesterol levels and reducing cardiovascular disease risk. Although generally well-tolerated, statins can induce myopathy, a major cause of non-adherence to treatment. Impaired mitochondrial function has been implicated in the development of statin-induced myopathy, but the underlying mechanism remains unclear. We have shown that simvastatin downregulates the transcription of TOMM40 and TOMM22, genes that encode major subunits of the translocase of the outer mitochondrial membrane (TOM) complex. Mitochondrial effects of knockdown of TOMM40 and TOMM22 in mouse C2C12 and primary human skeletal cell myotubes include impaired oxidative function, increased superoxide production, reduced cholesterol and CoQ levels, and disrupted markers of mitochondrial dynamics and morphology as well as increased mitophagy, with similar effects resulting from simvastatin exposure. Overexpression of TOMM40 and TOMM22 in simvastatin-treated mouse and human skeletal muscle cells rescued effects on markers of mitochondrial dynamics and morphology, but not oxidative function or cholesterol and CoQ levels. These results show that TOMM40 and TOMM22 have key roles in maintaining both mitochondrial dynamics and function and indicate that their downregulation by statin treatment results in mitochondrial effects that may contribute to statin-induced myopathy.

Purpose of Review: This paper reviews the effects of major macronutrients and specific dietary interventions on atherogenic dyslipidemia, a common trait characterized by increased concentrations of triglyceride-rich and small, dense LDL particles, and reduced HDL-cholesterol. Recent Findings: Studies have shown that reducing carbohydrate intake is the most effective dietary approach for managing atherogenic dyslipidemia, particularly in individuals with excess adiposity and/or metabolic syndrome. Plant protein sources can also be beneficial, possibly due to their content of phytochemicals. Whereas dietary guidelines emphasize limiting intake of saturated fat for reducing cardiovascular risk by lowering concentrations of LDL cholesterol, this has not been shown to have an impact on atherogenic dyslipidemia. Summary: Attenuation or reversal of atherogenic dyslipidemia can be achieved by adopting a dietary pattern that emphasizes moderating carbohydrate intake, in particular processed grains and added sugars, rather than by focusing primarily on limiting saturated fat and its effects on LDL-cholesterol.

Previous research of associations between statins and Alzheimer disease and Alzheimer disease-related dementias (AD/ADRDs) has been limited by short follow-up, small samples, and confounding. We aimed to estimate the association between the 1st statin prescription and incident AD/ADRD among members of a large population-based cohort of older adults. We used a cohort study design emulating a target trial using data from Kaiser Permanente Northern California (KPNC), an integrated health care delivery system. Participants were born before 1951 and KPNC members for 4+ years during 1997-2010. Embedded subsamples included sociodemographic and genetic data. Statin initiators were matched at first prescription ("baseline") with up to 5 "noninitiators" based on age and low-density lipoprotein cholesterol (LDL-C). Participants with extreme propensity scores were excluded. The outcome was time to incident AD/ADRD diagnosis, censoring, or the administrative end of study (December 31, 2020). Cox proportional hazard models were used to estimate hazard ratios for statin initiation on AD/ADRD incidence. Follow-up time was divided at the first year of follow-up to account for increased AD/ADRD detection in the first year due to increased interaction with the health care system after a statin prescription. Among eligible participants (n = 705,061), 264,294 individuals (37.5% of eligible participants) initiated any statin during 2001-2010 ("initiators"), of whom 249,613 (94.4%) were matched with 255,937 unique noninitiators to create the analytic sample (322,358 unique participants; mean age at baseline = 67.4 years; 55.1% female). The average follow-up was 11.8 years. In the first year after initiating statins, AD/ADRD diagnoses were elevated by 46% (hazard ratio [HR] = 1.46, 95% CI 1.42-1.53) compared with noninitiators. After 1 year, statin initiators experienced no difference in AD/ADRD incidence (full sample: HR = 1.00, 95% CI 0.99-1.01; subsample with survey covariates: HR = 1.01, 95% CI 0.98-1.06; subsample with survey and genetic covariates: HR = 0.97, 95% CI 0.91-1.07). Adjustment for sociodemographic covariates and apolipoprotein E e4 allele count did not materially change the findings. In this large emulated target trial, statin initiation was inconsistent with more than a 3% increase or decrease in the hazard of AD/ADRD after the first year of follow-up. This intent-to-treat analysis does not directly quantify effects of long-term exposure to statins. Associations in the first year likely reflect increased medical observation immediately after statin initiation. This emulated trial provides Class II evidence that statin initiation is not associated with AD/ADRD or AD incidence after the first year of follow-up.

Atherogenesis has been shown in mice to be dependent on activation of the NLRP3 inflammasome, a cytosolic innate immune sensor activated by a broad range of pathogen and damage associated molecular patterns, including oxidized LDL (oxLDL) in atherosclerosis. Previous work from our group has shown that knockdown of Translocase of Outer Mitochondrial Membrane 40 ( TOMM40), which encodes a component of the mitochondrial importer TOM complex, increases expression and activity of the nuclear receptor-family transcription factor, liver X receptor (LXR) in hepatocytes. As LXR agonists have been shown to inhibit NLRP3 activation, we confirmed the prediction that TOMM40 knockdown has this effect in THP-1 monocyte-derived macrophages. Further, we demonstrated that TOMM40 KD upregulates LXR-mediated macrophage expression of the ABCA1 and ABCG1 genes which encode transporters that promote cellular cholesterol efflux, the first step in reverse cholesterol transport to the liver. Taken together, these findings identify a novel mechanism whereby increased LXR activity induced by suppression of TOMM40 expression in macrophages may retard atherogenesis both by inhibiting inflammation and promoting reverse cholesterol transport.

Statins are a commonly prescribed cholesterol lowering drug class that can increase the risk of new-onset diabetes (NOD). To investigate the molecular mechanisms underlying this effect, we generated human induced pluripotent stem cells (iPSCs) from individuals identified from electronic health records of Kaiser Permanente of Northern California who were susceptible to developing NOD after statin initiation or controls who maintained stable fasting glucose on statin treatment. RNA-seq analysis of iPSCs incubated with atorvastatin, simvastatin or mock buffer for 24 hours identified the long non-coding RNA MIR194-2HG as a top candidate gene. Statin-induced increases in its expression were observed in NOD resistant controls, while statin-induced reductions occurred in NOD susceptible cases. MIR194-2HG encompasses two microRNA genes: MIR192 and MIR194-2 . The mature microRNA miR-192-5p, derived from the 5’ arm of MIR192 , was predicted to bind the 3’UTR of the glucagon like peptide 1 (GLP-1) receptor ( GLP1R ) transcript. Transfection of a rat insulinoma cell line INS-1 with a miR-192-5p mimic increased Glp1r transcript (1.41-fold) and protein (1.51-fold) levels compared to a scrambled control. Using a luciferase reporter containing the human GLP1R 3’UTR, miR-192-5p overexpression similarly increased luciferase signal (1.44-fold). The miR-192-5p mimic enhanced glucose stimulated insulin secretion (GSIS) in response to GLP1R agonists (1.64-1.81-fold) and rescued simvastatin-induced GSIS impairment in INS-1 cells. Wild-type mice treated with miR-192 AAV8 had improved glucose sensitivity. Islets isolated from these mice exhibited enhanced GLP-1 potentiated GSIS during perifusion ex vivo . These effects were absent in the DIRKO ( Glp1r/Gipr double knockout) mouse islets, consistent with the idea that miR-192 promotes GLP-1 mediated GSIS through GLP1R. These findings implicate MIR192 in statin-induced impairment of GSIS by modulating GLP1R, potentially contributing to the susceptibility to NOD in statin users.

Statin pharmacogenetic implementation guidelines are derived from evidence of primarily Eurocentrically biased study populations. Functional SLCO1B1 variants that are rare in these study populations have not been equitably investigated and are thus missing from guidelines. The objective of this precision medicine health equity study was to determine the clinical validity of understudied candidate functional SLCO1B1 variants common in people with 1,000 Genomes sub‐Saharan African superpopulation (1KG‐AFR‐like) genetic similarity. We conducted our analyses using the real‐world evidence of participants from three large, electronic health record‐linked biobanks. We used bilirubin levels (as an endogenous substrate of organic anion transporting polypeptide [OATP1B1] function) and severe statin‐induced myotoxicity phenotypes. Loss‐of‐function splice variant rs77271279 (P = 1.1 × 10⁻¹⁷) had the strongest association with elevated total bilirubin levels in Black participants (mean 84% AFR‐like genetic similarity) followed by missense variant rs59502379 (P = 7.4 × 10⁻¹²) then missense variant rs4149056 (P = 6.0 × 10⁻⁵). In an exploratory subset of the Black study population who used statins (n = 77 severe statin‐induced myotoxicity cases), rs59502379 (odds ratio [OR] = 2.85, 95% confidence interval [CI] 1.08–7.52), but not rs77271279 (OR = 1.75, 95% CI 0.62–4.73) was associated with myotoxicity. Sensitivity analyses in participants with >5% AFR‐like genetic similarity corroborated these findings. For white participants, rs77271279 and rs59502379 were rare precluding subsequent analyses. Our findings highlight the clinical relevance for understudied SLCO1B1 variants on pharmacogenetic testing panels with a potential immediate impact on reducing the risk of severe statin‐induced myotoxicity primarily in Black patients, a group historically excluded from genomic research. Future studies require larger statin user study populations with less heterogeneity by statin type.