Genome-Wide CRISPR Screen Identifies Phospholipid Scramblase 3 as the Biological Target of Mitoprotective Drug SS-31

Key Points

Background

The synthetic tetrapeptide Szeto–Schiller (SS)-31 shows promise in alleviating mitochondrial dysfunction associated with common diseases. However, the precise pharmacological basis of its mitoprotective effects remains unknown.

Methods

To uncover the biological targets of SS-31, we performed a genome-scale clustered regularly interspaced short palindromic repeats screen in human kidney-2, a cell culture model where SS-31 mitigates cisplatin-associated cell death and mitochondrial dysfunction. The identified hit candidate gene was functionally validated using knockout cell lines, small interfering RNA-mediated downregulation, and tubular epithelial–specific conditional knockout mice. Biochemical interaction studies were also performed to examine the interaction of SS-31 with the identified target protein.

Results

Our primary screen and validation studies in hexokinase 2 and primary murine tubular epithelial cells showed that phospholipid scramblase 3 (PLSCR3), an understudied inner mitochondrial membrane protein, was essential for the protective effects of SS-31. For in vivo validation, we generated tubular epithelial–specific knockout mice and found that Plscr3 gene ablation did not influence kidney function under normal conditions or affect the severity of cisplatin and rhabdomyolysis-associated AKI. However, Plscr3 gene deletion completely abrogated the protective effects of SS-31 during cisplatin and rhabdomyolysis-associated AKI. Biochemical studies showed that SS-31 directly binds to a previously uncharacterized N-terminal domain and stimulates PLSCR3 scramblase activity. Finally, PLSCR3 protein expression was found to be increased in the kidneys of patients with AKI.

Conclusions

PLSCR3 was identified as the essential biological target that facilitated the mitoprotective effects of SS-31 in vitro and in vivo.

Exogenous mitochondrial transfer increases energy expenditure and attenuates adiposity gains in mice with diet-induced obesity

Obesity is associated with chronic multi-system bioenergetic stress that may be improved by increasing the number of healthy mitochondria available across organ systems. However, treatments capable of increasing mitochondrial content are generally limited to endurance exercise training paradigms, which are not always sustainable long-term, let alone feasible for many patients with obesity. Recent studies have shown that local transfer of exogenous mitochondria from healthy donor tissues can improve bioenergetic outcomes and alleviate the effects of tissue injury in recipients with organ specific disease. Thus, the aim of this project was to determine the feasibility of systemic mitochondrial transfer for improving energy balance regulation in the setting of diet-induced obesity. We found that transplantation of mitochondria from lean mice into mice with diet-induced obesity attenuated adiposity gains by increasing energy expenditure and promoting the mobilization and oxidation of lipids. Additionally, mice that received exogenous mitochondria demonstrated improved glucose uptake, greater insulin responsiveness, and complete reversal of hepatic steatosis. These changes were, in part, driven by adaptations occurring in white adipose tissue. Together, these findings are proof-of-principle that mitochondrial transplantation is an effective therapeutic strategy for limiting the deleterious metabolic effects of diet-induced obesity in mice.

MON-LB019 Setmelanotide (RM-493) Reduces Food Intake and Rapidly Induces Weight Loss in a Mouse Model of Alström Syndrome

Introduction&nbsp; Alström&nbsp;syndrome (AS) is an autosomal recessive ciliopathy caused by mutations in&nbsp;ALMS1, which encodes a protein that localizes to centrosomes and basal bodies of primary cilia. Early emergence of obesity in&nbsp;patients with&nbsp;AS suggests a key role for ALMS1 in body weight regulation. Mice with non-functional Alms1 develop normal hypothalamic cilia, but these are not maintained postnatally. This suggests involvement of the central pathways regulating energy balance in the development of obesity in AS. Since leptin signaling has been shown to be impaired in the related ciliopathy Bardet-Biedl syndrome, we hypothesized that targeting central pathways downstream of leptin signaling would reduce food intake and body weight in&nbsp;Alms1-/-&nbsp;mice.&nbsp;&nbsp; Methods&nbsp; Dose-response for the selective melanocortin 1/4 receptor agonist RM-493 (Setmelanotide) in suppressing food intake was determined in 19-wk-old female&nbsp;Alms1-/-&nbsp;mice&nbsp;(n=3) and wild-type (WT) littermates (n=3), individually housed and receiving daily intraperitoneal injections of vehicle (3 d) followed by RM-493 (3 d). A separate cohort of 17-wk-old male (n=4) and female (n=4)&nbsp;Alms1-/-&nbsp;mice had food intake measured continuously in metabolic cages&nbsp;(CLAMS, Columbus Instruments). After determining baseline food intake, mice received vehicle (2 d), followed by RM-493 (3 d), then 3d of washout (no treatment). Repeated measures ANOVA was performed. Mean ± SE and nominal p-values are shown.&nbsp; Results&nbsp; In the dose-response study,&nbsp;Alms-/-&nbsp;and&nbsp;WT&nbsp;had&nbsp;food intake responses that were&nbsp;similar&nbsp;for&nbsp;40&nbsp;(p=0.72),&nbsp;but different&nbsp;for&nbsp;100, 250, and 1000 nmol/kg/d (p’s<0.05). We selected&nbsp;250&nbsp;nmol/kg/d&nbsp;as the dose for further investigation&nbsp;as&nbsp;food intake&nbsp;was unchanged&nbsp;in WT&nbsp;(p=0.23)&nbsp;but reduced&nbsp;in&nbsp;Alms1-/-&nbsp;(p=0.04). In&nbsp;the&nbsp;second cohort,&nbsp;food intake&nbsp;and&nbsp;body weight&nbsp;were&nbsp;similar&nbsp;at&nbsp;baseline&nbsp;compared to&nbsp;vehicle&nbsp;for&nbsp;both&nbsp;male and female&nbsp;Alms1-/-&nbsp;(p’s>0.84).&nbsp;RM-493&nbsp;(250 nmol/kg/d)&nbsp;reduced food intake&nbsp;in male&nbsp;Alms1-/- compared to vehicle (-46.4%;&nbsp;p=0.003), causing&nbsp;a&nbsp;nonsignificant&nbsp;reduction in body weight&nbsp;(-13.1%;&nbsp;p=0.33),&nbsp;whereas&nbsp;food intake&nbsp;in female&nbsp;Alms1-/-&nbsp;was&nbsp;reduced by 28.5%,&nbsp;and body weight by 6.5%,&nbsp;although&nbsp;neither difference was significant (p’s&nbsp;>0.61).&nbsp;During the washout period, male&nbsp;Alms1-/-&nbsp;ate 62.8% more food than during the vehicle period&nbsp;(p<0.0001),&nbsp;resulting in body weight regain&nbsp;of&nbsp;5.0 ± 0.7 g. Female&nbsp;Alms1-/-&nbsp;ate 24.8% more food&nbsp;during the washout period compared to&nbsp;vehicle&nbsp;(p=0.056),&nbsp;regaining&nbsp;2.4 ± 0.6 g of body weight.&nbsp;&nbsp;&nbsp; Conclusion&nbsp; RM-493&nbsp;acutely&nbsp;reduces food intake&nbsp;in&nbsp;Alms1-/-&nbsp;mice&nbsp;with a greater effect in males than females.&nbsp;Withdrawal of RM-493 results in compensatory overeating&nbsp;and&nbsp;rapid weight regain back to pre-treatment values. These findings identify RM-493 as a promising drug&nbsp;candidate&nbsp;for&nbsp;treating&nbsp;obesity in AS.&nbsp;The impact of RM-493 on long-term body weight will be determined in ongoing chronic treatment studies in&nbsp;Alms1-/-&nbsp;and WT mice. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.