The recently described phenomenon of cholesterol‐loaded low‐density lipoproteins (LDL) entering the arterial wall from the lumen by transcytosis has been accepted as an alternative for the long‐held concept that atherogenesis involves only passive LDL movement across an injured or dysfunctional endothelial barrier. This active transport of LDL can now adequately explain why plaques (atheromas) appear under an intact, uninjured endothelium. However, the LDL transcytosis hypothesis is still questionable, mainly because the process serves no clear physiological purpose. Moreover, central components of the putative LDL transcytosis apparatus are shared by the counter process of cholesterol efflux and reverse cholesterol transport (RCT) and therefore can essentially create an energy‐wasting futile cycle and paradoxically be pro‐ and antiatherogenic simultaneously. Hence, by critically reviewing the literature, we wish to put forward an alternative interpretation that, in our opinion, better fits the experimental evidence. We assert that most of the accumulating cholesterol (mainly as LDL) reaches the intima not from the lumen by transcytosis, but from the artery’s inner layers: the adventitia and media. We have named this directional cholesterol transport transmural cholesterol flux (TCF). We suggest that excess cholesterol, diffusing from the avascular (i.e., devoid of blood and lymph vessels) media’s smooth muscle cells, is cleared by the endothelium through its apical membrane. A plaque is formed when this cholesterol clearance rate lags behind its rate of arrival by TCF.

Anxiety and metabolic impairments are often inter-related, but the underlying mechanisms are unknown. To seek RNAs involved in the anxiety disorder–metabolic disorder link, we subjected zebrafish larvae to caffeine-induced anxiety or high-fat diet (HFD)-induced obesity followed by RNA sequencing and analyses. Notably, differentially expressed (DE) transcripts in these larval models and an adult zebrafish caffeine-induced anxiety model, as well as the transcript profiles of inherently anxious versus less anxious zebrafish strains and high-fat diet-fed versus standard diet-fed adult zebrafish, revealed inversely regulated DE transcripts. In both larval anxiety and obesity models, these included long noncoding RNAs and transfer RNA fragments, with the overrepresented immune system and inflammation pathways, e.g., the “interleukin signaling pathway” and “inflammation mediated by chemokine and cytokine signaling pathway”. In adulthood, overrepresented immune system processes included “T cell activation”, “leukocyte cell-cell adhesion”, and “antigen processing and presentation”. Furthermore, unlike adult zebrafish, obesity in larvae was not accompanied by anxiety-like behavior. Together, these results may reflect an antagonistic pleiotropic phenomenon involving a re-adjusted modulation of the anxiety–metabolic links with an occurrence of the acquired immune system. Furthermore, the HFD potential to normalize anxiety-upregulated immune-related genes may reflect the high-fat diet protection of anxiety and neurodegeneration reported by others.

The high‐density lipoprotein (HDL)‐associated enzyme paraoxonase 1 (PON1) is expressed almost exclusively in the liver and is then transported by HDL to the peripheral tissues. The lipophilic nature of PON1 enables its easy exchange between the lipoprotein and cell membranes in a process that is dependent on the HDL receptor scavenger receptor class B, type 1 (SR‐B1). In endothelial cells, PON1 binding to the cell membrane leads to its internalization by endocytosis and subsequent lysosomal degradation. PON1 is a “promiscuous” enzyme with unusually broad substrate specificity in vitro, but its actual function and substrate are still unknown. The enzyme requires a lipid environment and becomes completely inactive upon delipidation. However, when PON1 binds HDL, its active site faces the lipoprotein's core and is inaccessible to external substrates. Hence, the HDL‐bound PON1 is inactive toward substrates outside the particle's lipid core and is rapidly degraded and becomes inactive upon internalization. Consequently, the enzyme is only active in the cell membrane during its transit from HDL to the cytoplasm. To assign a function to PON1, we investigated whether it is a palmitoyl‐protein thioesterase (PPT) that can hydrolyze the palmitoyl moieties of membrane proteins involved in HDL and cholesterol transport, such as SR‐B1, ABCA1, or their neighboring caveola proteins to facilitate the release of HDL or trigger its endocytosis. This study shows that PON1 can hydrolyze palmitoyl‐cysteine thioester bonds in vitro, has direct or indirect PPT activity in vivo, and can significantly decrease the presence of SR‐B1 in the endothelial membrane.

Anxiety disorders often associate with metabolic impairments, but the underlying developmental and molecular mechanisms are yet unknown. To seek RNAs that may link anxiety and obesity, we subjected RNA from zebrafish larvae of a caffeine-induced anxiety model and a high fat diet (HFD)-induced obesity model to RNA-sequencing. We found differentially expressed genes in the larval anxiety and obesity models, including long noncoding RNAs and transfer fragment RNAs. Surprisingly, they were inversely regulated and comprised overrepresentation of immune system pathways, e.g., interleukin signaling and inflammation. Similarly, inverse regulation persisted in adulthood, but with different overrepresented immune system processes, e.g., T cell activation, leukocyte cell-cell adhesion and antigen processing and presentation. Furthermore, unlike the known link in adult zebrafish, obesity in zebrafish larvae was not accompanied by anxiety-like behavior. These results may reflect an antagonistic pleiotropic phenomenon involving re-adjusted modulation of the anxiety-metabolic links with the immune system. Furthermore, the HFD potential to normalize the anxiety-upregulated immune-related genes may explain previously reported protective roles of high fat diet in rodent anxiety and Alzheimer’s disease models.