This is the first study to assess whether optogenetic stimulation can induce contractions of the bladder detrusor muscle in diabetic rats, which serve as a model for detrusor underactivity. Diabetes-induced detrusor underactivity is a significant concern, and effective treatments are limited. Consequently, the development of novel therapeutic strategies is urgently required. Accordingly, we have explored the potential of the optogenetic approach. Optogenetics is a light-based modulation technique that employs genetic engineering to introduce light-sensitive ion channels into target cells via vectors, thereby enabling the activation or inhibition of muscle or nerve activity through light exposure (1). Building on our previous findings in normal rats, we aim to determine whether this light-based technique can effectively modulate bladder activity under diabetic conditions.

In this study, we utilized an adeno-associated virus (AAV) vector to deliver and express the Channelrhodopsin-2 (ChR2) transgene fused with the fluorescent protein tdTomato. This vector facilitates excitatory neuromuscular activation upon exposure to blue light (473 nm). For the diabetic rat model, nine-week-old female Sprague-Dawley rats received an intraperitoneal injection of streptozotocin, and only those with blood glucose levels exceeding 200 mg/dL were selected for further study. In the intervention group, the AAV vector was then injected directly into the bladder wall (Figure 1). After a four-week incubation period, cystometry was performed to assess detrusor function. During cystometry, the exposed bladder was irradiated with blue light for 60 seconds on two occasions, and changes in detrusor function were recorded before and after light exposure (Figure 1). Following cystometry, the bladder tissue was harvested for subsequent histological analysis. In the control group, diabetic rats that did not receive the AAV vector injection underwent cystometry under blue light irradiation, and changes in detrusor function were recorded in the same manner.

In the intervention group, data analysis was conducted on three diabetic rats with blood glucose levels ranging from 411 to 484 mg/dL. All rats exhibited a significant increase in bladder pressure upon blue light exposure. In one representative case, the median bladder pressure increased from 23.63 cmH₂O before exposure to 43.64 cmH₂O during blue light stimulation (p<0.05) (Figure 2). The urinary interval and voided volume remained unchanged. In contrast, no significant changes in intravesical pressure were observed in the control group, which consisted of three diabetic rats with blood glucose levels ranging from 201 to 417 mg/dL. Furthermore, in the intervention group, fluorescence immunostaining revealed strong signals for both tdTomato from the viral vector and peripherin. The merged images confirmed the co-localization of these markers in the bladder smooth muscle as observed under a confocal microscope.

The significant increase in intravesical pressure observed during blue light stimulation in diabetic rats suggests that optogenetic activation effectively induces contractions of the bladder smooth muscle, even under pathological conditions. Furthermore, the unchanged urinary interval and voided volume indicate that the stimulation selectively enhances contractile activity without affecting overall bladder storage or voiding patterns. Additionally, fluorescence immunostaining confirmed the successful targeting of the bladder smooth muscle, as evidenced by the co-localization of peripherin with the vector component.

These findings collectively support the potential of optogenetic neuromodulation as a promising approach for managing detrusor underactivity associated with diabetes.

Optogenetic Neuromodulation of the Urinary Bladder