Changes in the mitochondrial genetic system in rabbit urinary bladder after partial outlet obstruction
Authors:   , Nevel-McGarvey Christina A. 
Published: July 2024

In the rabbit, partial outlet obstruction of the urinary bladder results in acute overdistention and a rapid increase in mass which correlates with a mild decrease in its ability to empty. This thesis initiates an investigation of the status and expression of mitochondrial DNA in rabbit bladder tissue following partial outlet obstruction. During the first 7 d after partial outlet obstruction there was a significant decrease in activity for at least two mitochondrial enzymes associated with the Krebs cycle, citrate synthase and malate dehydrogenase, but the activity of the terminal electron acceptor in the electron transport system, cytochrome oxidase, decreased only slightly. The relative number of copies of the mitochondrial genome per cell progressively decreased as much as 10-fold during the first 7 d in obstructed tissues. Our data suggest that one mechanism responsible for compensated bladder function during the initial period following partial outlet obstruction is a massive up-regulation of mitochondrial transcript levels to support the function of the electron transport-oxidative phosphorylation machinery. The aberrant function of rabbit bladder after outlet obstruction is primarily related to severity of disease, rather than to the time after obstruction. In general, the greater the increase in mass and decrease in response to various stimuli, the greater the level of decompensation. We next sought to correlate mitochondrial genetic and biochemical studies with the severity of bladder disease, as defined by bladder mass. The data suggest that bladder dysfunction secondary to partial outlet obstruction is mediated in part by a significant loss in coordinate expression of mitochondrial and mitochondria-related nuclear genes, and by the consequent loss of enzymatic functions specified by those genes. We also test our hypothesis that reversal of obstruction during compensation, and the consequent return to normal physiological function, result from progressive return of mitochondrial and nuclear genetic functions to normal coordinate activity in bladder smooth muscle, and that the essentially irreversible loss of bladder function during decompensation is a consequence of its inability to maintain indefinitely powerful adaptive transcriptional compensation. We investigated the behavior of the mitochondrial and nuclear genetic systems in 28 d obstructed bladder tissues both before and after release from obstruction. While the mitochondrial transcriptional control system may remain aberrant even after release from obstruction, mitochondria-related nuclear systems can rapidly recover normal function post-reversal. Analysis of bladder tissues which had lower than normal mitochondrial genome copy number revealed that smooth muscle cells continued to lose mitochondrial DNA after reversal, and that transcripts from these DNA templates fell to well below normal from extremely high levels at the time of reversal. Although transcript levels did recover toward normal from extremely low levels, recovery from low levels of translation products was erratic. Taken together, these results show that in obstructed rabbit bladder tissue, reversal of obstruction results in recovery of the nuclear transcriptional control system, while the organellar transcriptional control system remains aberrant even when the relative mitochondrial genome copy number returns to normal. These observations suggest that the limiting factor for the return of bladder to normal function following reversal of obstruction is recovery of the mitochondrial transcriptional control system. Our results also suggest that in the obstructed urinary bladder, relative mitochondrial genome copy level, rather than gross hypertrophy and contractility, may be a more accurate indication of recoverability of the tissue before permanent damage ensues. (Abstract shortened by UMI.).