SS-31

Although age-associated changes in kidney glomerular architecture have been described in mice and man, the mechanisms are unknown. It is unclear if these changes can be prevented or even reversed by systemic therapies administered at advanced age. Using light microscopy and transmission electron microscopy, our results showed glomerulosclerosis with injury to mitochondria in glomerular epithelial cells in mice aged 26 months (equivalent to a 79-year-old human). To test the hypothesis that reducing mitochondrial damage in late age would result in lowered glomerulosclerosis, we administered the mitochondrial targeted peptide, SS-31, to aged mice. Baseline (24-month-old) mice were randomized to receive 8 weeks of SS-31, or saline, and killed at 26 months of age. SS-31 treatment improved age-related mitochondrial morphology and glomerulosclerosis. Assessment of glomeruli revealed that SS-31 reduced senescence (p16, senescence-associated-ß-Gal) and increased the density of parietal epithelial cells. However, SS-31 treatment reduced markers of parietal epithelial cell activation (Collagen IV, pERK1/2, and α-smooth muscle actin). SS-31 did not impact podocyte density, but it reduced markers of podocyte injury (desmin) and improved cytoskeletal integrity (synaptopodin). This was accompanied by higher glomerular endothelial cell density (CD31). Thus, despite initiating therapy in late-age mice, a short course of SS-31 has protective benefits on glomerular mitochondria, accompanied by temporal changes to the glomerular architecture. This systemic pharmacological intervention in old-aged animals limits glomerulosclerosis and senescence, reduces parietal epithelial cell activation, and improves podocyte and endothelial cell integrity.

Spinal cord injury (SCI) affects millions globally, leading to severe motor and sensory deficits with no effective clinical treatment. Cardiolipin (CL), a mitochondria-specific phospholipid, plays a critical role in bioenergetics and apoptosis. Emerging evidence suggests that CL alterations contribute to secondary SCI pathology, but their precise role and underlying mechanisms remain fully understudied. In this study, we investigated the protective effects of SS-31 on CL alteration, neuronal death, tissue damage, and behavioral recovery after SCI using both in vitro and in vivo models, lipidomics analysis, histological evaluation, and behavioral assessments. In vitro investigations used primary spinal cord neuron cultures, challenged with either rotenone or glutamatergic excitotoxicity, with protective capabilities measured via cell death assays and neurite morphological analysis. In vivo investigations used female adult C57Bl/6 mice, challenged with a contusive SCI. The results showed that SS-31 reduced rotenone- and glutamate-induced mitochondrial dysfunction and neuronal death in a dose-dependent manner in vitro. Additionally, SS-31 attenuated rotenone- and glutamate-induced neurite degeneration in vitro. Lipidomics analysis revealed a reduction in CL at 24 h post-SCI in adult mice, which was attenuated by SS-31 in a dose-dependent manner. Consistent with this effect, SS-31 improved behavioral recovery after SCI in adult mice, although it had no significant effect on tissue damage. These findings suggest that CL alteration may play a key role in the pathogenesis of SCI, at least in the C57BL/6 mouse, and as such could be an attractive therapeutic target for ameliorating secondary SCI.

Ischemic stroke is a severe cerebrovascular disorder characterized by a cascade of pathological processes, including neuroinflammation and apoptosis. These processes lead to high mortality rates and long-term disabilities, imposing substantial socioeconomic burdens. Although reperfusion therapies have improved patient outcomes, many remain ineligible due to narrow therapeutic windows or clinical contraindications. Consequently, developing novel neuroprotective strategies is of significant clinical importance. Elamipretide (SS-31) and nicotinamide mononucleotide (NMN) are well-documented neuroprotective agents operating through distinct mechanisms; however, their combined efficacy and underlying mechanisms in ischemic stroke remain elusive. This study investigated the neuroprotective efficacy of SS-31 and NMN, alone or in combination, in a mouse model of ischemic stroke, with a specific focus on their modulation of triggering receptor expressed on myeloid cells 2 (TREM2)-mediated neuroinflammatory and apoptotic pathways. A middle cerebral artery occlusion/reperfusion (MCAO/R) model was established in male mice, followed by treatment with SS-31, NMN, or their combination. Therapeutic outcomes were evaluated using neurobehavioral scoring, histopathological staining, transcriptomic sequencing, and protein expression analyses. TREM2 overexpression experiments and specific pharmacological inhibition of the NF-κB pathway were conducted to elucidate the specific molecular mechanisms. Co-administration of SS-31 and NMN significantly attenuated post-ischemic brain damage and ameliorated neurological deficits (P < 0.0001), demonstrating effects markedly superior to either monotherapy. Transcriptomic profiling revealed that the combination therapy specifically modulated innate immune and apoptotic pathways, concomitant with a significant downregulation of TREM2. Mechanistically, the combination therapy effectively inhibited NF-κB (p65) activation, thereby downregulating TREM2 expression. This suppression attenuated microglial activation, reduced the expression of canonical pro-inflammatory cytokines (IL-1β, TNF-α, and IL-6), and rebalanced the Bcl-2/Bax apoptotic axis. Overexpression of TREM2 entirely reversed these neuroprotective benefits. Combination therapy with SS-31 and NMN provides robust neuroprotection against ischemic stroke by suppressing the NF-κB/TREM2 signaling axis, thereby combinatorially modulating post-stroke neuroinflammation and apoptosis. These findings highlight a novel, multi-targeted strategy for precision stroke interventions.

Friedreich ataxia (FRDA) is a serious hereditary neurodegenerative disease, mostly accompanied with hypertrophic cardiomyopathy, caused by the reduced expression of frataxin (FXN). However, there is still no effective treatment. Our previous studies have shown that SS-31, a mitochondrion-targeted peptide, is capable to upregulate the expression of FXN and improve the mitochondrial function in cells derived from FRDA patients. To further explore the potential of SS-31, we used the GAA expansion-based models, including Y47 and YG8R (Fxn KIKO) mice, primary neurons and macrophages from the mice and cells derived from FRDA patients. After once-daily intraperitoneal injection of 1 mg/kg SS-31 for 1 month, we observed the significant improvement of motor function. The vacuolation in dorsal root ganglia, lesions in dentate nuclei and the lost thickness of myelin sheath of spinal cord were all repaired after SS-31 treatment. In addition, the hypertrophic cardiomyocytes and disarrayed abnormal Purkinje cells were dramatically reduced. Interestingly, we found that SS-31 treatment upregulated FXN expression not only at the translational levels as observed in cell culture but also at mRNA levels in vivo. Consequently, mitochondrial morphology and function were greatly improved in all tested tissues. Importantly, our data provided additional evidence that the maintenance of the therapeutic benefits needed continuous drug administration. Taken together, our findings have demonstrated the effectiveness of SS-31 treatment through the upregulation of FXN in vivo and offer guidance of the potential usage in the clinical application for FRDA.

Hepatic injury is common in patients who suffer from severe burns plus delayed resuscitation (B + DR). Stimulator of interferon genes (STING) is primarily expressed in Kupffer cells (KCs). We demonstrated that B + DR caused hepatic injury and oxidative stress. Reactive oxygen species (ROS) damage mitochondrial membranes in hepatocytes, leading to the release of mitochondrial DNA (mtDNA) into the hepatocyte cytosol and the circulation. The damaged hepatocytes then activate the mtDNA/STING pathway in KCs and trigger KCs polarization towards pro-inflammatory phenotype. SS-31 is a strong antioxidant that specifically concentrates in the inner mitochondrial membrane. SS-31 prevented hepatic injury by neutralizing ROS, inhibiting the release of mtDNA, protecting hepatocyte mitochondria, suppressing the activation of the mtDNA/STING pathway and inhibiting KCs polarization into pro-inflammatory phenotype.

BACKGROUND: Exercise intolerance, promoted by skeletal muscle- and mitochondrial dysfunction, has been identified as a therapeutic target in heart failure with preserved ejection fraction (HFpEF). In the context of mitochondrial dysfunction, altered cardiolipin integrity has been reported in the myocardium of HFpEF, suggesting Elamipretide, a cardiolipin stabilizing agent, as potential therapeutic approach. The present study investigated cardiolipin dysregulation in the skeletal muscle of HFpEF rats and analyzed the effect of Elamipretide treatment. METHODS: Female zucker fatty spontaneously hypertensive heart failure F1 hybrid lean (n=10, control) and obese rats (n=24, HFpEF) were included. At 20 weeks of age, HFpEF rats were randomized into 2 groups receiving NaCl (n=12) or Elamipretide (n=12) for 12 weeks. Skeletal muscle tissue was collected for whole-muscle force, single-fiber mechanics, mitochondrial respiration, histology and molecular analyses. RESULTS: HFpEF rats exhibited reduced cardiolipin levels (-6.8%, P=0.007) and maturation (shown via tafazzin expression), contractile dysfunction, titin hyperphosphorylation, fiber atrophy and increased oxidative stress markers. Elamipretide improved whole muscle (soleus: +8.2%, P=0.041, extensor digitorum longus: +10.9%, P=0.016) and single-fiber (soleus: +173.2%, P<0.001, extensor digitorum longus: +66.0%, P=ns) contractile function and titin phosphorylation (soleus: -35.4%, P<0.001, extensor digitorum longus: -40.2%, P<0.001), while preventing atrophy development (soleus: +49%, P=0.001, extensor digitorum longus: +54.8%, P<0.001). Improved mitochondrial function, presumably through cardiolipin-mediated improvements in oxidative phosphorylation, could be associated with muscle force and cardiolipin integrity. CONCLUSIONS: Our data highlight cardiolipin stabilization as a key modulator of mitochondrial and contractile function in HFpEF, identifying Elamipretide as a promising therapeutic approach for skeletal muscle dysfunction.