Gene and protein expression of dorsal root ganglion sensory receptors in normotensive and hypertensive male rats

Abstract

The exercise pressor reflex (EPR), a neurocirculatory control mechanism, is exaggerated in hypertensive humans and rats. Disease-related abnormalities within the afferent arm of the reflex loop, including mechano- and metabosensitive receptors located at the terminal end of group III/IV muscle afferents, may contribute to the dysfunctional EPR in hypertension. Using control (WKY) and spontaneous hypertensive (SHR) rats, we examined dorsal root ganglion (DRG) gene and protein expression of molecular receptors recognized as significant determinants of the EPR. Twelve lumbar DRGs (6 left, 6 right) were harvested from each of 10 WKY [arterial blood pressure (MAP): 96 ± 9 mmHg] and 10 SHR (MAP: 144 ± 9 mmHg). DRGs from the left side were used for protein expression (Western blotting; normalized to GAPDH), whereas right-side DRGs (i.e., parallel structure) were used to determine mRNA levels (RNA-sequencing, normalized to TPM). Analyses focused on metabosensitive (ASIC3, Bradykinin receptor B2, EP4, P2X3, TRPv1) and mechanosensitive (Piezo1/2) receptors. Although Piezo1 was similar in both groups (P = 0.75), protein expression for all other receptors was significantly higher in SHR compared with WKY. With the exception of a greater Bradykinin-receptor B2 in SHR (P < 0.05), mRNA expression of all other receptors was not different between groups (P > 0.18). The higher protein content of these sensory receptors in SHR indirectly supports the previously proposed hypothesis that the exaggerated EPR in hypertension is, in part, due to disease-related abnormalities within the afferent arm of the reflex loop. The upregulated receptor content, combined with normal mRNA levels, insinuates that posttranscriptional regulation of sensory receptor protein expression might be impaired in hypertension.

Keywords: blood pressure; dorsal root ganglion; exercise pressor reflex; hypertension; mRNA.

Figure 1.

Representative Western Blots of molecular dorsal root ganglion receptors in normotensive (Wistar-Kyoto, WKY, n = 4) and hypertensive (spontaneously hypertensive rats, SHR, n = 4) male rats.

Figure 2.

Protein expression of molecular dorsal root ganglion (DRG) receptors in normotensive (Wistar-Kyoto, WKY, n = 10) and hypertensive (spontaneously hypertensive rat, SHR, n = 10) male rats. In the box plots, the boundary of the box closest to zero indicates the 1st quartile, a black line within the box marks the median, and the boundary of the box farthest from zero indicates the 3rd quartile. Asterisk represents group mean. Whiskers represent the lowest and highest values which are not outliers. Points above and below the whiskers indicate outliers identified as 1.5 times interquartile range above the 3rd quartile or below the 1st quartile. A priori, unpaired Student’s t tests were used to test group differences. Data are means ± SD. #P < 0.05 vs. WKY.

Figure 3.

Quantity of mRNA in dorsal root ganglion (DRG) of normotensive (Wistar-Kyoto, WKY, n = 10) and hypertensive (spontaneously hypertensive rat, SHR, n = 10) male rats. A priori, unpaired Student’s t tests were used to test group differences. Data are means ± SD. #P < 0.05 vs. WKY.