Lactate and ketone bodies play important roles as alternative energy substrates, especially in conditions with a decreased utility of glucose. Short-chain fatty acids (acetate, propionate, and butyrate), produced by bacterial fermentation, supply most of the energy substrates in ruminants such as the cow and sheep. These monocarboxylates are transfered through the plasma membrane by proton-coupled monocarboxylate transporters (MCTs) and sodium-coupled MCTs (SMCTs). To reveal the metabolism and functional significance of monocarboxylates, the cellular localization of MCTs and SMCTs together with the expressed intensities holds great importance. This paper reviews the immunohistochemical localization of SMCTs and major MCT subtypes throughout the mammalian body. MCTs and SMCTs display a selective membrane-bound localization with porality. In contrast to the limited expression of SMCTs in the intestine and kidney, MCTs display a broader distribution pattern than GLUTs. The brain, kidney, placenta, and male genital tract express multiple subtypes of the MCT family. Determination of the cellular localization of MCTs is most controversial in the brain, possibly due to regional differences and the transcriptional modification of MCT proteins. Information on the localization of MCTs and SMCTs aids in understanding the nutrient absorption and metabolism throughout the mammalian body. In some cases, the body may use monocarboxylates as signal molecules, like hormones.
CD36 is a broadly expressed transmembrane protein that engages multiple ligands, including polar lipids. This protein is thought to even contribute to the chemosensory detection of long-chain fatty acids in the oral cavity of rodents. In this study, we assessed whether animals consciously perceive a ligand of CD36, 1-(palmitoyl)-2-(5-keto-6-octanedioyl)phosphatidylcholine (KOdiA-PC), and if so, whether CD36 is involved in sensing the oxidised phospholipid species. We found that mice avoided or hesitated to ingest fluids containing KOdiA-PC, suggesting a conscious perception of the lipid in the animals. We assessed the involvement and role of CD36 in the KOdiA-PC perception by comparing the behavioural responses of wild-type and CD36-deficient mice to the test fluids, and provided evidence that the protein could play a role in sensing a lower level of the lipid. We also found that transection of the olfactory nerve of wild-type mice resulted in an inability to perceive KOdiA-PC, suggesting the significance of olfactory system in the lipid sensing. Our findings, coupled with the recent finding of CD36 expression in the mouse olfactory epithelium, led us to predict that the site of CD36 action in the KOdiA-PC sensing plausibly lies within the nasal cavity of the animal.
Proteinuria is not only a hallmark of renal complication in malignant hypertension, but is also a major deteriorating factor for the progression to end-stage renal disease. Podocyte injury plays a crucial role in the renal damage associated with hypertensive nephropathy, but the underlying mechanism remains unclear. Malignant stroke-prone spontaneously hypertensive rats (MSHRSP/Kpo) represent an original and useful model of human malignant hypertension. In this study, we disclosed the glomerular injuries in the MSHRSP/Kpo. MSHRSP/Kpo exhibited elevated blood pressure at 6 weeks along with renal dysfunction and proteinuria. Histological analysis of the MSHRSP/Kpo glomeruli revealed a severe atrophy, but no change was found in the podocyte number. The expression levels of podocyte-specific proteins, nephrin, podocin, and synaptopodin were decreased in the MSHRSP/Kpo glomeruli, though another podocyte-specific protein, CD2AP, in the MSHRSP/Kpo glomeruli exhibited a similar extent of staining as in normotensive WKY/Kpo rats. Furthermore, desmin was not markedly detected in the WKY/Kpo glomeruli, but was strongly positive in MSHRSP/Kpo. By electron microscopy, well-formed foot processes (FP) were replaced by effacement in MSHRSP/Kpo. An original malignant hypertension strain MSHRSP/Kpo exhibits podocyte injuries associated with the decrease of some podocyte-specific proteins and the upregulation of desmin, along with FP effacement and proteinuria.
Tensin2 (Tns2) is thought to be a component of the cytoskeletal structures linking actin filaments with focal adhesions and is known to play a role as an intracellular signal transduction mediator through integrin in podocytes, although the mechanism by which it functions remains unclear. A Tns2-null mutation (nph) leads to massive albuminuria following podocyte foot process effacement in the ICGN mice, the origin of the mutation, and the DBA/2J (D2) mice, but not in the C57BL/6J (B6) mice or 129+Ter/SvJcl (129T) mice. Elucidating the reasons for these differences in diverse genetic backgrounds could help in unraveling Tns2 function in podocytes. We produced congenic mice in which Tns2nph was introgressed into a FVB/NJ background (FVB-Tns2nph), and evaluated the progression of kidney disease. FVB-Tns2nph mice developed albuminuria, renal fibrosis and renal anemia as seen in ICGN mice. The FVB-Tns2nph mice demonstrated podocyte foot process alteration under an electron microscope by as early as 4 weeks of age. This revealed that FVB strain is susceptible to Tns2-deficiency.
The renal glomeruli in lower vertebrates display mesangium-like cells and matrices interposed between the capillary endothelium and the basement membrane, while those in mammals reportedly lack such interpositions except in pathological conditions. By combined scanning and transmission electron microscopic observations, the pericapillary mesangial tissues were comparatively analyzed in four vertebrate classes: mammals (rats and rabbits), reptiles (green iguanas), amphibians (bullfrogs), and teleosts (carps). The observations discriminated three types of pericapillary interposition. The first, acellular interpositions, occurred universally, with mammalians displaying rudimental ones. This tissue type corresponded with extracellular matrices held in subendothelial grooves which were supported by fine endothelial projections anchored to the basement membrane. In lower vertebrates these grooves constituted an anastomosed system of subendothelial channels that communicated with the mesangial region, to favor cleaning of the glomerular filter. The second, compound type was specific to reptiles and amphibians, affecting the entire capillary circumference in the latter. In this tissue type, fine mesangial processes—which accompanied considerable amounts of fibrillar matrices—were loosely associated with the endothelial bases, indicating their possible nature as a kind of myofibroblast. Occurrence of the third, cellular interpositions was confined to small incidental loci in mammalian and teleost glomeruli. This tissue type was mostly occupied by thick processes or main bodies of the mesangial cells that tightly interlocked their short marginal microvilli with corresponding indentations on the endothelial bases.
We investigated the anti-obesity effects of Brazilian green propolis ethanol extract using a mouse model of obesity. Repeated intraperitoneal injection of propolis (100 mg/kg twice a week) caused feeding suppression in C57BL/6 mice, whereas this treatment had negligible effects on C57BL/6 ob/ob mice. Since C57BL/6 ob/ob mice have a missense mutation in the Lep gene, leptin is likely to contribute to the propolis-induced feeding suppression. We found that propolis treatment indeed clearly increased leptin mRNA production in the visceral adipose tissues. Moreover, propolis extract directly elevated leptin expression in differentiated 3T3-L1 adipocytes. Artepillin C, an important organic compound found in Brazilian green propolis, failed to induce leptin mRNA in 3T3-L1 cells. Compounds other than artepillin C in Brazilian propolis must thus cause leptin induction in adipocytes, possibly resulting in the suppression of feeding and obesity.