Functional role of histamine receptors in the renal cortical collecting duct cells.

Histamine is an important immunomodulator, as well as a regulator of allergic inflammation, gastric acid secretion, and neurotransmission. Although substantial histamine level has been reported in the kidney, renal pathological and physiological effects of this compound have not been clearly defined. The goal of this study was to provide insight into the role of histamine-related pathways in the kidney, with emphasis on the collecting duct (CD), a distal part of the nephron important for the regulation of blood pressure. We report that all four histamine receptors (HRs) as well as enzymes responsible for histamine metabolism and synthesis are expressed in cultured mouse mpkCCDcl4 cells, and histamine evokes a dose-dependent transient increase in intracellular Ca2+ in these cells. Furthermore, we observed a dose-dependent increase in cAMP in the CD cells in response to histamine. Short-circuit current studies aimed at measuring Na+ reabsorption via ENaC (epithelial Na+ channel) demonstrated inhibition of ENaC-mediated currents by histamine after a 4-h incubation, and single-channel patch-clamp analysis revealed similar ENaC open probability before and after acute histamine application. The long-term (4 h) effect on ENaC was corroborated in immunocytochemistry and qPCR, which showed a decrease in protein and gene expression for αENaC upon histamine treatment. In summary, our data highlight the functional importance of HRs in the CD cells and suggest potential implications of histamine in inflammation-related renal conditions. Further research is required to discern the molecular pathways downstream of HRs and assess the role of specific receptors in renal pathophysiology.

The implications of histamine metabolism and signaling in renal function.

Inflammation is an essential part of the immune response; it has been found to be central to the disruption of kidney function in acute kidney injury, diabetic nephropathy, hypertension, and other renal conditions. One of the well-known mediators of the inflammatory response is histamine. Histamine receptors are expressed throughout different tissues, including the kidney, and their inhibition has proven to be a viable strategy for the treatment of many inflammation-associated diseases. Here, we provide an overview of the current knowledge regarding the role of histamine and its metabolism in the kidney. Establishing the importance of histamine signaling for kidney function will enable new approaches for the treatment of kidney diseases associated with inflammation.

Renal Glomerular Mitochondria Function in Salt-Sensitive Hypertension.

Salt-sensitive (SS) hypertension is accompanied with an early onset of proteinuria, which results from the loss of glomerular podocytes. Here, we hypothesized that glomerular damage in the SS hypertension occurs in part due to mitochondria dysfunction, and we used a unique model of freshly isolated glomeruli to test this hypothesis. In order to mimic SS hypertension, we used Dahl SS rats, an established animal model. Animals were fed a 0.4% NaCl (normal salt, NS) diet or challenged with a high salt (HS) 4% NaCl diet for 21 days to induce an increase in blood pressure (BP). Similar to previous studies, we found that HS diet caused renal hypertrophy, increased BP, glomerulosclerosis, and renal lesions such as fibrosis and protein casts. We did not observe changes in mitochondrial biogenesis in the renal cortex or isolated glomeruli fractions. However, Seahorse assay performed on freshly isolated glomeruli revealed that basal mitochondrial respiration, maximal respiration, and spare respiratory capacity were lower in the HS compared to the NS group. Using confocal imaging and staining for mitochondrial H2O2 using mitoPY1, we detected an intensified response to an acute H2O2 application in the podocytes of the glomeruli isolated from the HS diet fed group. TEM analysis showed that glomerular mitochondria from the HS diet fed group have structural abnormalities (swelling, enlargement, less defined cristae). Therefore, we report that glomerular mitochondria in SS hypertension are functionally and structurally defective, and this impairment could eventually lead to loss of podocytes and proteinuria. Thus, the glomerular-mitochondria axis can be targeted in novel treatment strategies for hypertensive glomerulosclerosis.

Long noncoding RNA complementarity and target transcripts abundance.

Eukaryotic mRNA metabolism regulates its stability, localization, and translation using complementarity with counter-part RNAs. To modulate their stability, small and long noncoding RNAs can establish complementarity with their target mRNAs. Although complementarity of small interfering RNAs and microRNAs with target mRNAs has been studied thoroughly, partial complementarity of long noncoding RNAs (lncRNAs) with their target mRNAs has not been investigated clearly. To address that research gap, our lab investigated whether the sequence complementarity of two lncRNAs, lincRNA-p21 and OIP5-AS1, influenced the quantity of target RNA expression. We predicted a positive correlation between lncRNA complementarity and target mRNA quantity. We confirmed this prediction using RNA affinity pull down, microarray, and RNA-sequencing analysis. In addition, we utilized the information from this analysis to compare the quantity of target mRNAs when two lncRNAs, lincRNA-p21 and OIP5-AS1, are depleted by siRNAs. We observed that human and mouse lincRNA-p21 regulated target mRNA abundance in complementarity-dependent and independent manners. In contrast, affinity pull down of OIP5-AS1 revealed that changes in OIP5-AS1 expression influenced the amount of some OIP5-AS1 target mRNAs and miRNAs, as we predicted from our sequence complementarity assay. Altogether, the current study demonstrates that partial complementarity of lncRNAs and mRNAs (even miRNAs) assist in determining target RNA expression and quantity.

Profiling of m6A RNA modifications identified an age-associated regulation of AGO2 mRNA stability.

Gene expression is dynamically regulated in a variety of mammalian physiologies. During mammalian aging, there are changes that occur in protein expression that are highly controlled by the regulatory steps in transcription, post-transcription, and post-translation. Although there are global profiles of human transcripts during the aging processes available, the mechanism(s) by which transcripts are differentially expressed between young and old cohorts remains unclear. Here, we report on N6-methyladenosine (m6A) RNA modification profiles of human peripheral blood mononuclear cells (PBMCs) from young and old cohorts. An m6A RNA profile identified a decrease in overall RNA methylation during the aging process as well as the predominant modification on proteincoding mRNAs. The m6A-modified transcripts tend to be more highly expressed than nonmodified ones. Among the many methylated mRNAs, those of DROSHA and AGO2 were heavily methylated in young PBMCs which coincided with a decreased steady-state level of AGO2 mRNA in the old PBMC cohort. Similarly, downregulation of AGO2 in proliferating human diploid fibroblasts (HDFs) also correlated with a decrease in AGO2 mRNA modifications and steady-state levels. In addition, the overexpression of RNA methyltransferases stabilized AGO2 mRNA but not DROSHA and DICER1 mRNA in HDFs. Moreover, the abundance of miRNAs also changed in the young and old PBMCs which are possibly due to a correlation with AGO2 expression as observed in AGO2-depleted HDFs. Taken together, we uncovered the role of mRNA methylation on the abundance of AGO2 mRNA resulting in the repression of miRNA expression during the process of human aging.