Preservation of cochlear function in Fabp3 (H-Fabp) knockout mice

Fatty acid binding protein type 7 deficiency preserves auditory function in noise-exposed mice

Fatty acid-binding protein 7 (FABP7) is vital for uptake and trafficking of fatty acids in the nervous system. To investigate the involvement of FABP7 in noise-induced hearing loss (NIHL) pathogenesis, we used Fabp7 knockout (KO) mice generated via CRISPR/Cas9 in the C57BL/6 background. Initial auditory brainstem response (ABR) measurements were conducted at 9 weeks, followed by noise exposure at 10 weeks. Subsequent ABRs were performed 24 h later, with final measurements at 12 weeks. Inner ears were harvested 24 h after noise exposure for RNA sequencing and metabolic analyses. We found no significant differences in initial ABR measurements, but Fabp7 KO mice showed significantly lower thresholds in the final ABR measurements. Hair cell survival was also enhanced in Fabp7 KO mice. RNA sequencing revealed that genes associated with the electron transport chain were upregulated or less impaired in Fabp7 KO mice. Metabolomic analysis revealed various alterations, including decreased glutamate and aspartate in Fabp7 KO mice. In conclusion, FABP7 deficiency mitigates cochlear damage following noise exposure. This protective effect was supported by the changes in gene expression of the electron transport chain, and in several metabolites, including excitotoxic neurotransmitters. Our study highlights the potential therapeutic significance of targeting FABP7 in NIHL.

Effects of enriched endogenous omega-3 fatty acids on age-related hearing loss in mice

Objective

Dietary intervention is a practical prevention strategy for age-related hearing loss (AHL). Omega-3 (n-3) polyunsaturated fatty acids (PUFAs) may be effective in prevention of AHL due to their anti-inflammatory and tissue-protective functions. Age-related changes in the hearing function of wild-type and Fat-1 transgenic mice derived from the C57BL/6N strain, which can convert omega-6 PUFAs to n-3 PUFAs and consequently produce enriched endogenous n-3 PUFAs, were investigated to test the efficacy of n-3 PUFAs for AHL prevention.

Results

At 2 months, the baseline auditory brainstem response (ABR) thresholds were the same in Fat-1 and wild-type mice at 8–16 kHz but were significantly higher in Fat-1 mice at 4 and 32 kHz. In contrast, the ABR thresholds of Fat-1 mice were significantly lower at 10 months. Moreover, the ABR thresholds of Fat-1 mice at low-middle frequencies were significantly lower at 13 months (12 kHz). Body weights were significantly reduced in Fat-1 mice at 13 months, but not at 2, 10, and 16–17 months. In conclusion, enriched endogenous n-3 PUFAs produced due to the expression of the Fat-1 transgene partially alleviated AHL in male C57BL/6N mice.

"Passenger gene" problem in transgenic C57BL/6 mice used in hearing research

Despite recent advances in genome engineering technologies, traditional transgenic mice generated on a mixed genetic background of C57BL/6 and 129/Sv mice remain widely used in age-related hearing loss (AHL) research, since C57BL/6 mice exhibit early onset and progression of AHL due to a mutation in cadherin 23-encoding gene (Cdh23^753G>A). In these transgenic mice, backcrossing for more than 10 generations results in replacement of the donor background (129/Sv) with that of the recipient (C57BL/6), so that approximately 99.9% of genes are C57BL/6-derived and are considered congenic. However, the regions flanking the target gene may still be of 129/Sv origin, creating a so-called "passenger gene problem" where the normal 129/Sv-derived Cdh23^753G allele can travel with the target gene. In this study, we investigated the role of fatty acid-binding protein 7 (Fabp7), which is important for cellular uptake and intracellular trafficking of fatty acids in the cochlea, using traditional Fabp7 knockout (KO) mice on the C57BL/6 background. We found that Fabp7 KO mice showed delayed AHL progression and milder cochlear degeneration. However, the genotype of the Cdh23 region flanking Fabp7 was still that of 129/Sv origin (Cdh23^753GG). Our findings reveal the potential risk of contamination for traditional transgenic mice generated on the C57BL/6 background.

Heart-type fatty acid-binding protein in cardiovascular disease: A systemic review

Fatty acid-binding proteins, whose clinical applications have been studied, are a family of proteins that reflect tissue injury. Heart-type fatty acid-binding protein (H-FABP) is a marker of ongoing myocardial damage and useful for early diagnosis of acute myocardial infarction (AMI). In the past decade, compared to other cardiac enzymes, H-FABP has shown more promise as an early detection marker for AMI. However, the role of H-FABP is being re-examined due to recent refinement in the search for newer biomarkers, and greater understanding of the role of high-sensitivity troponin. We discuss the current role of H-FABP as an early marker for AMI in the era of high sensitive troponin. H-FABP is highlighted as a prognostic marker for a broad spectrum of fatal diseases, viz., AMI, heart failure, arrhythmia, and pulmonary embolism that could be associated with poor clinical outcomes. Because the cut-off value of what constitutes an abnormal H-FABP potentially differs for each cardiovascular event and depends on the clinical setting, an optimal cut-off value has not been clearly established. Of note, several factors such as age, gender, and cardiovascular risk factors, which affect H-FABP levels need to be considered in this context. In this review, we discuss the clinical applications of H-FABP as a prognostic marker in various clinical settings.

Fatty acid binding proteins and the nervous system: Their impact on mental conditions

The brain is rich in lipid and fatty molecules. In this review article, we focus on fatty acid binding proteins (Fabps) that bind to fatty acids such as arachidonic acid and docosahexianoic acid and transfer these lipid ligands within the cytoplasm. Among Fabp family molecules, Fabp3, Fabp5, and Fabp7 are specifically localized in neural stem/progenitor cells, neurons and glia in a cell-type specific manner. Quantitative trait locus analysis has revealed that Fabp7 is related with performance of prepulse inhibition (PPI) that is used as an endophenotype of psychiatric diseases such as schizophrenia. Fabp5 and Fabp7 play important roles on neurogenesis and differentially regulate acoustic startle response and PPI. However, other behavior performances including spatial memory, anxiety-like behavior, and diurnal changes in general activity were not different in mice deficient for Fabp7 or Fabp5. Considering the importance of fatty acids in neurogenesis, we would like to emphasize that lipid nutrition and its dynamism via Fabps play significant roles in mental conditions. This might provide a good example of how nutritional environment can affect psychiatric conditions at the molecular level.