TGF-β1 and connexin-43 expression in neurogenic bladder from rats with sacral spinal cord injury

Assessing Neurogenic Lower Urinary Tract Dysfunction after Spinal Cord Injury: Animal Models in Preclinical Neuro-Urology Research

Neurogenic bladder dysfunction is a condition that affects both bladder storage and voiding function and remains one of the leading causes of morbidity after spinal cord injury (SCI). The vast majority of individuals with severe SCI develop neurogenic lower urinary tract dysfunction (NLUTD), with symptoms ranging from neurogenic detrusor overactivity, detrusor sphincter dyssynergia, or sphincter underactivity depending on the location and extent of the spinal lesion. Animal models are critical to our fundamental understanding of lower urinary tract function and its dysfunction after SCI, in addition to providing a platform for the assessment of potential therapies. Given the need to develop and evaluate novel assessment tools, as well as therapeutic approaches in animal models of SCI prior to human translation, urodynamics assessment techniques have been implemented to measure NLUTD function in a variety of animals, including rats, mice, cats, dogs and pigs. In this narrative review, we summarize the literature on the use of animal models for cystometry testing in the assessment of SCI-related NLUTD. We also discuss the advantages and disadvantages of various animal models, and opportunities for future research.

Expression of transforming growth factor-β1 and autophagy markers in the bladder of rats with neurogenic lower urinary tract injury

OBJECTIVE

This study was conducted to explore the expression of transforming growth factor-beta 1 (TGF-β1) and its correlation with autophagy markers in the bladder of rats with neurogenic lower urinary tract dysfunction (NLUTD) post spinal cord injury (SCI).

STUDY DESIGN

A total of 36 male Wistar rats were randomly divided into the SCI group and control group. Rats in the SCI group were subjected to T10-T11 spinal cord transection. At day 1, 4, and 7, 6 rats were euthanized daily and the Basso, Beattie and Bresnahan score (BBB score), post-void residual (PVR), urinary bladder function score (UBFS) and bladder weight were assessed. The expression TGF-β1 and autophagy markers were evaluated by immunofluorescence staining, Western bolt, and qRT-PCR.

SETTING

A total of 36 male Wistar rats were randomly divided into the SCI group and control group, with three time points in each group.

PARTICIPANTS

Not applicable.

RESULTS

SCI modeling impaired the motor function of the hind limbs and the bladder function of rats. NLUTD muscle exhibited a punctated immunostaining pattern for LC3, suggesting the accumulation of autophagosomes. Our results further indicated that compared with the control group, the expression levels of TGF-β1 and LC3 were increased, while the level of P62 was decreased after SCI modeling.

CONCLUSION

TGF-β1 was significantly increased in SCI rats with NLUTD and was correlated with autophagy markers LC3 and p62.

Pathogenesis evidence from human and animal models of detrusor underactivity

Detrusor underactivity (DU) is a common urodynamic diagnosis in patients with lower urinary tract symptoms and large post-voiding residual volume. Animal and human studies showed the possible etiologies of DU include central or peripheral nerve injury, bladder outlet obstruction, chronic ischemia, aging, diabetes mellitus, and sympathetic inhibition of micturition reflex. Evidence from animal and human DU studies with various etiologies revealed highly similar gross and histological characteristics in the bladders, including increased bladder weight, bladder wall thickening, inflammation, collagen deposition, and fibrosis. In electron microscopy, smooth muscle destruction, swollen mitochondria, decreased nerve innervation, caveolae, and umbrella cell fusiform vesicles were noted in the DU bladders. Most animal DU models demonstrate detrusor contractility changes from compensatory to the decompensatory stage, and the change was compatible with human DU observation. The cystometry in the DU animal studies is characterized by impaired contractility, prolong intercontraction interval, and hyposensation, while in vitro bladder muscle strips experiment may exhibit normal detrusor contractility. Decreased bladder blood flow and increased oxidative stress in bladders had been proved in different animal DU models, suggesting they should be important in the DU pathogenesis pathway. Sensory receptors mRNA and protein expression changes in DU bladders had been observed in both animal and human studies, including muscarinic receptors M2, M3, adrenergic receptor β3, purinergic receptor P2X1, P2X3, and transient receptor potential vanilloid (TRPV) 1 and TRPV4. Although some of the sensory receptors changes remain controversial, it might be the target for further pharmacologic treatments.

Establishment of animal model manifested as bladder neurogenic changes generated by bilateral pelvic nerve injury in male rats

PURPOSE

To establish a male rat model of neurogenic bladder after bilateral pelvic nerve injury (BPNI) and investigate the factors associated with onset of neurogenic bladder.

METHODS

Twenty-four 8-week-old male Sprague-Dawley rats were randomly divided into three groups (n = 8 rats per group). Rats in 4-week and 8-week nerve injury group underwent BPNI, while rats in the sham group underwent a sham operation. Bladder functional analysis were performed and then bladders tissues were harvested for morphological examination and investigating the mRNA expression levels of target genes in all rats.

RESULTS

The bladder weight significantly increased in rats following BPNI. Functional analysis revealed non-voiding contractions and decreased detrusor contractility following BPNI, manifested as elevated post-void residual and bladder capacity while reduced maximum voiding pressure and voiding efficiency. The collagen area in bladder tissue and mRNA expression levels of target genes significantly increased at 4 or 8 weeks post-BPNI except Smad3. At 4 weeks post-BPNI, expression levels of vesicular acetylcholine transporter were reduced, then returned to baseline at 8 weeks. Expression levels of tyrosine hydroxylase were reduced at both 4 and 8 weeks post-BPNI.

CONCLUSIONS

A neurogenic bladder animal model was successfully established by performing BPNI in male rats, characterized by impaired voiding function, bladder detrusor fibrosis, and reduced neurotransmitter release.

Mechanosensitivity Is a Characteristic Feature of Cultured Suburothelial Interstitial Cells of the Human Bladder

Bladder dysfunction is characterized by urgency, frequency (pollakisuria, nocturia), and dysuria and may lead to urinary incontinence. Most of these symptoms can be attributed to disturbed bladder sensitivity. There is growing evidence that, besides the urothelium, suburothelial interstitial cells (suICs) are involved in bladder afferent signal processing. The massive expansion of the bladder during the filling phase implicates mechanical stress delivered to the whole bladder wall. Little is known about the reaction of suICs upon mechanical stress. Therefore, we investigated the effects of mechanical stimulation in cultured human suICs. We used fura-2 calcium imaging as a major physiological readout. We found spontaneous intracellular calcium activity in 75 % of the cultured suICs. Defined local pressure application via a glass micropipette led to local increased calcium activity in all stimulated suICs, spreading over the whole cell. A total of 51% of the neighboring cells in a radius of up to 100 µm from the stimulated cell showed an increased activity. Hypotonic ringer and shear stress also induced calcium transients. We found an 18-times increase in syncytial activity compared to unstimulated controls, resulting in an amplification of the primary calcium signal elicited in single cells by 50%. Our results speak in favor of a high sensitivity of suICs for mechanical stress and support the view of a functional syncytium between suICs, which can amplify and distribute local stimuli. Previous studies of connexin expression in the human bladder suggest that this mechanism could also be relevant in normal and pathological function of the bladder in vivo.

TGF-β1 facilitates cell-cell communication in osteocytes via connexin43- and pannexin1-dependent gap junctions

Connexins and pannexins are two families of channel forming proteins that are able to pass small molecules to achieve communication between cells. While connexins have been recognized to mediate gap junctional intercellular communication (GJIC), pannexins are far less known. Our previous study reported the potential role of TGF-β1 in mediating of connexins in osteocytes in vitro. Herein, we aimed to elucidate the influence of TGF-β1 on cell-cell communication based on gap junctions assembled by connexins and pannexins in vitro and ex vivo. We first showed that TGF-β1 positively affected the elongation of dendritic processes of osteocytes. Our data indicated that TGF-β1 increased expressions of connexin43 (Cx43) and pannexin1 (panx1), which are indispensable for hemichannel formation in gap junctions, in osteocytes in vitro and ex vivo. TGF-β1 enhanced gap junction formation and impacted cell-cell communication in living osteocytes, as indicated by the scrape loading and Lucifer yellow transfer assays. TGF-β1 enhanced the expressions of Cx43 and panx1 via activation of ERK1/2 and Smad3/4 signalling. The TGF-β1-restored expressions of Cx43 and panx1 in osteocytes in the presence of an ERK inhibitor, U0126, further demonstrated the direct participation of Smad3/4 signalling. TGF-β1 increased the accumulation of Smad3 in the nuclear region (immunofluorescence assay) and promoted the enrichment of Smad3 at the binding sites of the promoters of Gja1 (Cx43) and Panx1 (ChIP assay), thereby initiating the enhanced gene expression. These results provide a deep understanding of the molecular mechanisms involved in the modulation of cell-cell communication in osteocytes induced by TGF-β1.