Pharmacological Targeting of Mitochondria in Diabetic Kidney Disease.

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) in the United States and many other countries. DKD occurs through a variety of pathogenic processes that are in part driven by hyperglycemia and glomerular hypertension, leading to gradual loss of kidney function and eventually progressing to ESRD. In type 2 diabetes, chronic hyperglycemia and glomerular hyperfiltration leads to glomerular and proximal tubular dysfunction. Simultaneously, mitochondrial dysfunction occurs in the early stages of hyperglycemia and has been identified as a key event in the development of DKD. Clinical management for DKD relies primarily on blood pressure and glycemic control through the use of numerous therapeutics that slow disease progression. Because mitochondrial function is key for renal health over time, therapeutics that improve mitochondrial function could be of value in different renal diseases. Increasing evidence supports the idea that targeting aspects of mitochondrial dysfunction, such as mitochondrial biogenesis and dynamics, restores mitochondrial function and improves renal function in DKD. We will review mitochondrial function in DKD and the effects of current and experimental therapeutics on mitochondrial biogenesis and homeostasis in DKD over time. SIGNIFICANCE STATEMENT: Diabetic kidney disease (DKD) affects 20% to 40% of patients with diabetes and has limited treatment options. Mitochondrial dysfunction has been identified as a key event in the progression of DKD, and pharmacologically restoring mitochondrial function in the early stages of DKD may be a potential therapeutic strategy in preventing disease progression.

Discovering Novel Plasma Biomarkers for Ischemic Stroke: Lipidomic and Metabolomic Analyses in an Aged Mouse Model.

Ischemic stroke remains a leading cause of mortality and long-term disability worldwide, necessitating efforts to identify biomarkers for diagnosis, prognosis, and treatment monitoring. The present study aimed to identify novel plasma biomarkers of neurodegeneration and inflammation in a mouse model of stroke induced by distal middle cerebral artery (MCA) occlusion. Using targeted lipidomic and global untargeted metabolomic profiling of plasma collected from aged male mice 24 hours after stroke and weekly thereafter for 7 weeks, we discovered distinct acute and chronic signatures. In the acute phase, we observed elevations in myelin-associated lipids, including sphingomyelin (SM) and hexosylceramide (HCER) lipid species, indicating brain lipid catabolism. In the chronic phase, we identified 12-hydroxyeicosatetraenoic acid (12-HETE) as a putative biomarker of prolonged inflammation, consistent with our previous observation of a biphasic pro-inflammatory response to ischemia in the mouse brain. These results provide insight into the metabolic alterations detectable in the plasma after stroke and highlight the potential of myelin degradation products and arachidonic acid derivatives as biomarkers of neurodegeneration and inflammation, respectively. These discoveries lay the groundwork for further validation in human studies and may improve stroke management strategies.

Formoterol alters chemokine expression and ameliorates pain behaviors after moderate spinal cord injury in female mice.

Secondary spinal cord injury (SCI) is characterized by increased cytokines and chemokines at the site of injury that have been associated with the development of neuropathic pain. Nearly 80% of SCI patients report suffering from chronic pain, which is poorly managed with available analgesics. While treatment with the FDA-approved ß2-adrenergic receptor agonist, formoterol, improves various aspects of recovery post-SCI in vivo, its effects on cytokines, chemokines and neuropathic pain remain unknown. Female mice were subjected to moderate (60 kdyn) or severe (80 kdyn) SCI followed by daily treatment with vehicle or formoterol (0.3 mg/kg, i.p.) beginning 8h after injury. The expression of pro-inflammatory cytokines/chemokines, such as IP-10, MIP-1a, MCP-1, BCA-1 and NF-κB, was increased in the injury site of vehicle-treated mice 24h post-SCI, which was ameliorated with formoterol treatment, regardless of injury severity. Thermal hyperalgesia and mechanical allodynia, as measured by Hargreaves infrared apparatus and von Frey filaments, respectively, were assessed prior to SCI and then weekly beginning 21 days post injury (DPI). While all injured mice exhibited decreased withdrawal latency following thermal stimulation compared to baseline, formoterol treatment reduced this response ~15% by 35 DPI. Vehicle-treated mice displayed significant mechanical allodynia, as evidenced by a 55% decrease in withdrawal threshold from baseline. In contrast, mice treated with formoterol maintained a consistent withdrawal time at all times tested. These data indicate that formoterol reduces inflammation post-SCI, likely contributing to mitigation of neuropathic pain, and further supporting the therapeutic potential of this treatment strategy. Significance Statement Chronic pain is a detrimental consequence of spinal cord injury (SCI). We show that treatment with the FDA-approved drug formoterol after SCI decreases injury site pro-inflammatory chemo/cytokines and alters markers of glial cell activation and infiltration. Additionally, formoterol treatment improves locomotor function and body composition, and decreases lesion volume. Finally, formoterol treatment decreased mechanical allodynia and thermal hyperalgesia post-SCI. These data are suggestive of the mechanism of formoterol-induced recovery, and further indicate its potential as a therapeutic strategy for SCI.

Serotonin regulation of mitochondria in kidney diseases.

Serotonin, while conventionally recognized as a neurotransmitter in the CNS, has recently gained attention for its role in the kidney. Specifically, serotonin is not only synthesized in the kidney, but it also regulates glomerular function, vascular resistance, and mitochondrial homeostasis. Because of serotonin's importance to mitochondrial health, this review is focused on the role of serotonin and its receptors in mitochondrial function in the context of acute kidney injury, chronic kidney disease, and diabetic kidney disease, all of which are characterized by mitochondrial dysfunction and none of which has approved pharmacological treatments. Evidence indicates that activation of certain serotonin receptors can stimulate mitochondrial biogenesis (MB) and restore mitochondrial homeostasis, resulting in improved renal function. Serotonin receptor agonists that induce MB are therefore of interest as potential therapeutic strategies for renal injury and disease. SIGNIFICANCE STATEMENT: Mitochondrial dysfunction is associated with many human renal diseases such as acute kidney injury, chronic kidney disease, and diabetic kidney disease, which are associated with increased morbidity and mortality. Unfortunately, none of these pathologies has an FDA-approved pharmacological intervention, underscoring the urgency of identifying new therapeutics for such disorders. Studies show that induction of mitochondrial biogenesis via serotonin (5-hydroxytryptamine, 5-HT) receptors reduces kidney injury markers, restores mitochondrial and renal function after kidney injury, and decreases mortality, suggesting that targeting 5-HT receptors may be a promising therapeutic avenue for mitochondrial dysfunction in kidney diseases. While numerous reviews describe the importance of mitochondria and mitochondrial quality control mechanisms in kidney disease, the relevance of 5-HT receptor-mediated mitochondrial metabolic modulation in the kidney has yet to be thoroughly explored.

Repeated Administration of 2-Hydroxypropyl-ß-Cyclodextrin (HPßCD) Attenuates the Chronic Inflammatory Response to Experimental Stroke.

Globally, more than 67 million people are living with the effects of ischemic stroke. Importantly, many stroke survivors develop a chronic inflammatory response that may contribute to cognitive impairment, a common and debilitating sequela of stroke that is insufficiently studied and currently untreatable. 2-Hydroxypropyl-ß-cyclodextrin (HPßCD) is an FDA-approved cyclic oligosaccharide that can solubilize and entrap lipophilic substances. The goal of the present study was to determine whether the repeated administration of HPßCD curtails the chronic inflammatory response to stroke by reducing lipid accumulation within stroke infarcts in a distal middle cerebral artery occlusion mouse model of stroke. To achieve this goal, we subcutaneously injected young adult and aged male mice with vehicle or HPßCD 3 times per week, with treatment beginning 1 week after stroke. We evaluated mice at 7 weeks following stroke using immunostaining, RNA sequencing, lipidomic, and behavioral analyses. Chronic stroke infarct and peri-infarct regions of HPßCD-treated mice were characterized by an upregulation of genes involved in lipid metabolism and a downregulation of genes involved in innate and adaptive immunity, reactive astrogliosis, and chemotaxis. Correspondingly, HPßCD reduced the accumulation of lipid droplets, T lymphocytes, B lymphocytes, and plasma cells in stroke infarcts. Repeated administration of HPßCD also preserved NeuN immunoreactivity in the striatum and thalamus and c-Fos immunoreactivity in hippocampal regions. Additionally, HPßCD improved recovery through the protection of hippocampal-dependent spatial working memory and reduction of impulsivity. These results indicate that systemic HPßCD treatment following stroke attenuates chronic inflammation and secondary neurodegeneration and prevents poststroke cognitive decline.SIGNIFICANCE STATEMENT Dementia is a common and debilitating sequela of stroke. Currently, there are no available treatments for poststroke dementia. Our study shows that lipid metabolism is disrupted in chronic stroke infarcts, which causes an accumulation of uncleared lipid debris and correlates with a chronic inflammatory response. To our knowledge, these substantial changes in lipid homeostasis have not been previously recognized or investigated in the context of ischemic stroke. We also provide a proof of principle that solubilizing and entrapping lipophilic substances using HPßCD could be an effective strategy for treating chronic inflammation after stroke and other CNS injuries. We propose that using HPßCD for the prevention of poststroke dementia could improve recovery and increase long-term quality of life in stroke sufferers.

Lasmiditan promotes recovery from acute kidney injury through induction of mitochondrial biogenesis.

Acute kidney injury (AKI) involves rapid loss of renal function and occurs in 8-16% of hospitalized patients. AKI can be induced by drugs, sepsis, and ischemia-reperfusion (I/R). Hallmarks of AKI include mitochondrial and microvasculature dysfunction as well as renal tubular injury. There is currently no available therapeutic for AKI. Previously, our group identified that serotonin (5-HT)1F receptor agonism with lasmiditan accelerated endothelial cell recovery and induced mitochondrial biogenesis (MB) in vitro. We hypothesized that lasmiditan, a Federal Drug Administration-approved drug, would induce MB and improve microvascular and renal function in a mouse model of AKI. Male mice were subjected to renal I/R and treated with lasmiditan (0.3 mg/kg) or vehicle beginning 24 h after injury and then daily until euthanasia at 6 or 12 days. Serum creatinine was measured to estimate glomerular filtration rate. The renal cortex was assessed for mitochondrial density, vascular permeability and integrity, tubular damage, and interstitial fibrosis. Lasmiditan increased mitochondrial number (1.4-fold) in renal cortices. At 6 days, serum creatinine decreased 41% in the I/R group and 72% with lasmiditan. At 6 or 12 days, kidney injury molecule-1 increased in the I/R group and decreased 50% with lasmiditan. At 12 days, interstitial fibrosis decreased with lasmiditan by 50% and collagen type 1 by 38%. Evan's blue dye leakage increased 2.5-fold in the I/R group and was restored with lasmiditan. The tight junction proteins zonula occludens-1, claudin-2, and claudin-5 decreased in the I/R group and recovered with lasmiditan. At 6 or 12 days, peroxisome proliferator-activated receptor-γ coactivator-1α and electron transport chain complexes increased only with lasmiditan. In conclusion, lasmiditan treatment beginning AKI induces MB, attenuated vascular and tubular injury, decreased interstitial fibrosis, and lowered serum creatinine. Given that lasmiditan is a Federal Drug Administration-approved drug, these preclinical data support repurposing lasmiditan as a therapeutic for AKI.NEW & NOTEWORTHY AKI pathology involves a rapid decline in kidney function and occurs in 8-16% of hospitalized patients. There is currently no therapeutic for AKI. AKI results in mitochondria dysfunction, microvasculature injury, and loss of renal tubular function. In an I/R-induced AKI mouse model, treatment with the FDA-approved 5-HT1F receptor-selective agonist lasmiditan induced mitochondrial biogenesis, improved vascular integrity, reduced fibrosis, and reduced proximal tubule damage. These data support repurposing lasmiditan for the treatment of AKI.

Boosting Mitochondrial Biogenesis Diminishes Foam Cell Formation in the Post-Stroke Brain.

Following ischemic stroke, the degradation of myelin and other cellular membranes surpasses the lipid-processing capabilities of resident microglia and infiltrating macrophages. This imbalance leads to foam cell formation in the infarct and areas of secondary neurodegeneration, instigating sustained inflammation and furthering neurological damage. Given that mitochondria are the primary sites of fatty acid metabolism, augmenting mitochondrial biogenesis (MB) may enhance lipid processing, curtailing foam cell formation and post-stroke chronic inflammation. Previous studies have shown that the pharmacological activation of the ß2-adrenergic receptor (ß2-AR) stimulates MB. Consequently, our study sought to discern the effects of intensified ß2-AR signaling on MB, the processing of brain lipid debris, and neurological outcome using a mouse stroke model. To achieve this goal, aged mice were treated with formoterol, a long-acting ß2-AR agonist, daily for two and eight weeks following stroke. Formoterol increased MB in the infarct region, modified fatty acid metabolism, and reduced foam cell formation. However, it did not reduce markers of post-stroke neurodegeneration or improve recovery. Although our findings indicate that enhancing MB in myeloid cells can aid in the processing of brain lipid debris after stroke, it is important to note that boosting MB alone may not be sufficient to significantly impact stroke recovery.

Kidney targeting of formoterol containing polymeric nanoparticles improves recovery from ischemia reperfusion-induced acute kidney injury in mice.

The ß2 adrenergic receptor agonist, formoterol, is an inducer of mitochondrial biogenesis and restorer of mitochondrial and kidney function in acute and chronic models of kidney injury. Unfortunately, systemic administration of formoterol has the potential for adverse cardiovascular effects, increased heart rate, and decreased blood pressure. To minimize these effects, we developed biodegradable and biocompatible polymeric nanoparticles containing formoterol that target the kidney, thereby decreasing the effective dose, and lessen cardiovascular effects while restoring kidney function after injury. Male C57Bl/6 mice, treated with these nanoparticles daily, had reduced ischemia-reperfusion-induced serum creatinine and kidney cortex kidney injury molecule-1 levels by 78% and 73% respectively, compared to control mice six days after injury. With nanoparticle therapy, kidney cortical mitochondrial number and proteins reduced by ischemic injury, recovered to levels of sham-operated mice. Tubular necrosis was reduced 69% with nanoparticles treatment. Nanoparticles improved kidney recovery even when the dosing frequency was reduced from daily to two days per week. Finally, compared to treatment with formoterol-free drug alone, these nanoparticles did not increase heart rate nor decrease blood pressure. Thus, targeted kidney delivery of formoterol-containing nanoparticles is an improvement in standard formoterol therapy for ischemia-reperfusion-induced acute kidney injuries by decreasing the dose, dosing frequency, and cardiac side effects.

Post-Stroke Administration of the p75 Neurotrophin Receptor Modulator, LM11A-31, Attenuates Chronic Changes in Brain Metabolism, Increases Neurotransmitter Levels, and Improves Recovery.

The aim of this study was to test whether poststroke oral administration of a small molecule p75 neurotrophin receptor (p75NTR) modulator (LM11A-31) can augment neuronal survival and improve recovery in a mouse model of stroke. Mice were administered LM11A-31 for up to 12 weeks, beginning 1 week after stroke. Metabolomic analysis revealed that after 2 weeks of daily treatment, mice that received LM11A-31 were distinct from vehicle-treated mice by principal component analysis and had higher levels of serotonin, acetylcholine, and dopamine in their ipsilateral hemisphere. LM11A-31 treatment also improved redox homeostasis by restoring reduced glutathione. It also offset a stroke-induced reduction in glycolysis by increasing acetyl-CoA. There was no effect on cytokine levels in the infarct. At 13 weeks after stroke, adaptive immune cell infiltration in the infarct was unchanged in LM11A-31-treated mice, indicating that LM11A-31 does not alter the chronic inflammatory response to stroke at the site of the infarct. However, LM11A-31-treated mice had less brain atrophy, neurodegeneration, tau pathology, and microglial activation in other regions of the ipsilateral hemisphere. These findings correlated with improved recovery of motor function on a ladder test, improved sensorimotor and cognitive abilities on a nest construction test, and less impulsivity in an open field test. These data support small molecule modulation of the p75NTR for preserving neuronal health and function during stroke recovery. SIGNIFICANCE STATEMENT: The findings from this study introduce the p75 neurotrophin receptor as a novel small molecule target for promotion of stroke recovery. Given that LM11A-31 is in clinical trials as a potential therapy for Alzheimer's disease, it could be considered as a candidate for assessment in stroke or vascular dementia studies.

PDE5 inhibition rescues mitochondrial dysfunction and angiogenic responses induced by Akt3 inhibition by promotion of PRC expression.

Akt3 regulates mitochondrial content in endothelial cells through the inhibition of PGC-1α nuclear localization and is also required for angiogenesis. However, whether there is a direct link between mitochondrial function and angiogenesis is unknown. Here we show that Akt3 depletion in primary endothelial cells results in decreased uncoupled oxygen consumption, increased fission, decreased membrane potential, and increased expression of the mitochondria-specific protein chaperones, HSP60 and HSP10, suggesting that Akt3 is required for mitochondrial homeostasis. Direct inhibition of mitochondrial homeostasis by the model oxidant paraquat results in decreased angiogenesis, showing a direct link between angiogenesis and mitochondrial function. Next, in exploring functional links to PGC-1α, the master regulator of mitochondrial biogenesis, we searched for compounds that induce this process. We found that, sildenafil, a phosphodiesterase 5 inhibitor, induced mitochondrial biogenesis as measured by increased uncoupled oxygen consumption, mitochondrial DNA content, and voltage-dependent anion channel protein expression. Sildenafil rescued the effects on mitochondria by Akt3 depletion or pharmacological inhibition and promoted angiogenesis, further supporting that mitochondrial homeostasis is required for angiogenesis. Sildenafil also induces the expression of PGC-1 family member PRC and can compensate for PGC-1α activity during mitochondrial stress by an Akt3-independent mechanism. The induction of PRC by sildenafil depends upon cAMP and the transcription factor CREB. Thus, PRC can functionally substitute during Akt3 depletion for absent PGC-1α activity to restore mitochondrial homeostasis and promote angiogenesis. These findings show that mitochondrial homeostasis as controlled by the PGC family of transcriptional activators is required for angiogenic responses.

Time-to-treatment window and cross-sex potential of ß2-adrenergic receptor-induced mitochondrial biogenesis-mediated recovery after spinal cord injury.

Mitochondrial dysfunction is a well-characterized consequence of spinal cord injury (SCI). We previously reported that treatment with the FDA-approved ß2-adrenergic receptor agonist formoterol beginning 8 h post-SCI induces mitochondrial biogenesis (MB) and improves body composition and locomotor recovery in female mice. To determine the time-to-treatment window of formoterol, female mice were subjected to 80 kdyn contusion SCI and daily administration of vehicle or formoterol (0.3 mg/kg) beginning 24 h after injury. This delayed treatment paradigm improved body composition in female mice by 21 DPI, returning body weight to pre-surgery weight and restoring gastrocnemius mass to sham levels; however, there was no effect on locomotor recovery, as measured by the Basso-Mouse Scale (BMS), or lesion volume. To assess the cross-sex potential of formoterol, injured male mice were treated with vehicle or formoterol (0.3 or 1.0 mg/kg) beginning 8 h after SCI. Formoterol also improved body composition post-SCI in male mice, restoring body weight and muscle mass regardless of dose. Interestingly, however, improved BMS scores and decreased lesion volume was observed only in male mice treated with 0.3 mg/kg. Additionally, 0.3 mg/kg formoterol induced MB in the gastrocnemius and injured spinal cord, as evidenced by increased MB protein expression and mitochondrial number. These data indicate that formoterol treatment improves recovery post-SCI in both male and female mice in a dose- and initiation time-dependent manner. Furthermore, formoterol-induced functional recovery post-SCI is not directly associated with peripheral effects, such as muscle mass and body weight.

Extracellular signal-regulated kinase 1/2 regulates NAD metabolism during acute kidney injury through microRNA-34a-mediated NAMPT expression.

Prior studies have established the important role of extracellular signal-regulated kinase 1/2 (ERK1/2) as a mediator of acute kidney injury (AKI). We demonstrated rapid ERK1/2 activation induced renal dysfunction following ischemia/reperfusion (IR)-induced AKI and downregulated the mitochondrial biogenesis (MB) regulator, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) in mice. In this study, ERK1/2 regulation of cellular nicotinamide adenine dinucleotide (NAD) and PGC-1α were explored. Inhibition of ERK1/2 activation during AKI in mice using the MEK1/2 inhibitor, trametinib, attenuated renal cortical oxidized NAD (NAD+) depletion. The rate-limiting NAD biosynthesis salvage enzyme, NAMPT, decreased following AKI, and this decrease was prevented by ERK1/2 inhibition. The microRNA miR34a decreased with the inhibition of ERK1/2, leading to increased NAMPT protein. Mice treated with a miR34a mimic prevented increases in NAMPT protein in the renal cortex in the presence of ERK1/2 inhibition. In addition, ERK1/2 activation increased acetylated PGC-1α, the less active form, whereas inhibition of ERK1/2 activation prevented an increase in acetylated PGC-1α after AKI through SIRT1 and NAD+ attenuation. These results implicate IR-induced ERK1/2 activation as an important contributor to the downregulation of both PGC-1α and NAD+ pathways that ultimately decrease cellular metabolism and renal function. Inhibition of ERK1/2 activation prior to the initiation of IR injury attenuated decreases in PGC-1α and NAD+ and prevented kidney dysfunction.

Elucidation of cGMP-dependent induction of mitochondrial biogenesis through PKG and p38 MAPK in the kidney.

Previous studies have shown that cGMP increases mitochondrial biogenesis (MB). Our laboratory has determined that formoterol and LY344864, agonists of the ß2-adrenergic receptor and 5-HT1F receptor, respectively, signal MB in a soluble guanylyl cyclase (sGC)-dependent manner. However, the pathway between cGMP and MB produced by these pharmacological agents in renal proximal tubule cells (RPTCs) and the kidney has not been determined. In the present study, we showed that treatment of RPTCs with formoterol, LY344864, or riociguat, a sGC stimulator, induces MB through protein kinase G (PKG), a target of cGMP, and p38, an associated downstream target of PKG and a regulator of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) expression in RPTCs. We also examined if p38 plays a role in PGC-1α phosphorylation in vivo. Administration of l-skepinone, a potent and specific inhibitor of p38α and p38ß, to naïve mice inhibited phosphorylated PGC-1α localization in the nuclear fraction of the renal cortex. Taken together, we demonstrated a pathway, sGC/cGMP/PKG/p38/PGC-1α, for pharmacological induction of MB and the importance of p38 in this pathway.

Regulation of mitochondrial dynamics and energetics in the diabetic renal proximal tubule by the ß2-adrenergic receptor agonist formoterol.

Diabetes is a prevalent metabolic disease that contributes to ∼50% of all end-stage renal disease and has limited treatment options. We previously demonstrated that the ß2-adrenergic receptor agonist formoterol induced mitochondrial biogenesis and promoted recovery from acute kidney injury. Here, we assessed the effects of formoterol on mitochondrial dysfunction and dynamics in renal proximal tubule cells (RPTCs) treated with high glucose and in a mouse model of type 2 diabetes. RPTCs exposed to 17 mM glucose exhibited increased electron transport chain (ETC) complex I, II, III, and V protein levels and reduced ATP levels and uncoupled oxygen consumption rate compared with RPTCs cultured in the absence of glucose or osmotic controls after 96 h. ETC proteins, ATP, and oxygen consumption rate were restored in RPTCs treated with formoterol. RPTCs exposed to high glucose had increased phospho-dynamin-related protein 1 (Drp1), a mitochondrial fission protein, and decreased mitofusin 1 (Mfn1), a mitochondrial fusion protein. Formoterol treatment restored phospho-Drp1 and Mfn1 to control levels. Db/db and nondiabetic (db/m) mice (10 wk old) were treated with formoterol or vehicle for 3 wk and euthanized. Db/db mice showed increased renal cortical ETC protein levels in complexes I, III, and V and decreased ATP; these changes were prevented by formoterol. Phospho-Drp1 was increased and Mfn1 was decreased in db/db mice, and formoterol restored both to control levels. Together, these findings demonstrate that hyperglycemic conditions in vivo and exposure of RPTCs to high glucose similarly alter mitochondrial bioenergetic and dynamics profiles and that treatment with formoterol can reverse these effects. Formoterol may be a promising strategy for treating early stages of diabetic kidney disease.

Formoterol, a ß2-adrenoreceptor agonist, induces mitochondrial biogenesis and promotes cognitive recovery after traumatic brain injury.

Traumatic brain injury (TBI) leads to acute necrosis at the site of injury followed by a sequence of secondary events lasting from hours to weeks and often years. Targeting mitochondrial impairment following TBI has shown improvements in brain mitochondrial bioenergetics and neuronal function. Recently formoterol, a highly selective ß2-adrenoreceptor agonist, was found to induce mitochondrial biogenesis (MB) via Gßγ-Akt-eNOS-sGC pathway. Activation of MB is a novel approach that has been shown to restore mitochondrial function in several disease and injury models. We hypothesized that activation of MB as a target of formoterol after TBI would mitigate mitochondrial dysfunction, enhance neuronal function and improve behavioral outcomes. TBI-injured C57BL/6 male mice were injected (i.p.) with vehicle (normal saline) or formoterol (0.3 mg/kg) at 15 min, 8 h, 16 h, 24 h and then daily after controlled cortical impact (CCI) until euthanasia. After CCI, mitochondrial copy number and bioenergetic function were decreased in the ipsilateral cortex of the CCI-vehicle group. Compared to CCI-vehicle, cortical and hippocampal mitochondrial respiration rates as well as cortical mitochondrial DNA copy number were increased in the CCI-formoterol group. Mitochondrial Ca2+ buffering capacity in the hippocampus was higher in the CCI-formoterol group compared to CCI-vehicle group. Both assessments of cognitive performance, novel object recognition (NOR) and Morris water maze (MWM), decreased following CCI and were restored in the CCI-formoterol group. Although no changes were seen in the amount of cortical tissue spared between CCI-formoterol and CCI-vehicle groups, elevated levels of hippocampal neurons and improved white matter sparing in the corpus callosum were observed in CCI-formoterol group. Collectively, these results indicate that formoterol-mediated MB activation may be a potential therapeutic target to restore mitochondrial bioenergetics and promote functional recovery after TBI.

5-hydroxytryptamine 1F Receptor Agonist Induces Mitochondrial Biogenesis and Promotes Recovery from Spinal Cord Injury.

Spinal cord injury (SCI) is characterized by vascular disruption leading to ischemia, decreased oxygen delivery, and loss of mitochondrial homeostasis. This mitochondrial dysfunction results in loss of cellular functions, calcium overload, and oxidative stress. Pharmacological induction of mitochondrial biogenesis (MB) may be an effective approach to treat SCI. LY344864, a 5-hydroxytryptamine 1F (5-HT1F) receptor agonist, is a potent inducer of MB in multiple organ systems. To assess the efficacy of LY344864-induced MB on recovery post-SCI, female mice were subjected to moderate force-controlled impactor-induced contusion SCI followed by daily LY344864 administration for 21 days. Decreased mitochondrial DNA and protein content was present in the injury site 3 days post-SCI. LY344864 treatment beginning 1 h after injury attenuated these decreases, indicating MB. Additionally, injured mice treated with LY344864 displayed decreased Evan's Blue dye accumulation in the spinal cord compared with vehicle-treated mice 7 days after injury, suggesting restoration of vascular integrity. LY344864 also increased locomotor capability, with treated mice reaching a Basso-Mouse Scale score of 3.4 by 21 days, whereas vehicle-treated mice exhibited a score of 1.9. Importantly, knockout of the 5-HT1F receptor blocked LY344864-induced recovery. Remarkably, a similar degree of locomotor restoration was observed when treatment initiation was delayed until 8 h after injury. Furthermore, cross-sectional analysis of the spinal cord 21 days after injury revealed decreased lesion volume with delayed LY344864 treatment initiation, emphasizing the potential clinical applicability of this therapeutic approach. These data provide evidence that induction of MB via 5-HT1F receptor agonism may be a promising strategy for the treatment of SCI. SIGNIFICANCE STATEMENT: Treatment with LY344864 induces mitochondrial biogenesis in both the naive and injured mouse spinal cord. In addition, treatment with LY344864 beginning after impactor-induced contusion spinal cord injury improves mitochondrial homeostasis, blood-spinal cord barrier integrity, and locomotor function within 7 days. Importantly, similar locomotor results are observed whether treatment is initiated at 1 h after injury or 8 h after injury. These data indicate the potential for pharmacological induction of mitochondrial biogenesis through a 5-hydroxytryptamine 1F agonist as a novel therapeutic approach for spinal cord injury.

Mitochondrial biogenesis induced by the ß2-adrenergic receptor agonist formoterol accelerates podocyte recovery from glomerular injury.

Podocytes have limited ability to recover from injury. Here, we demonstrate that increased mitochondrial biogenesis, to meet the metabolic and energy demand of a cell, accelerates podocyte recovery from injury. Analysis of events induced during podocyte injury and recovery showed marked upregulation of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a transcriptional co-activator of mitochondrial biogenesis, and key components of the mitochondrial electron transport chain. To evaluate our hypothesis that increasing mitochondrial biogenesis enhanced podocyte recovery from injury, we treated injured podocytes with formoterol, a potent, specific, and long-acting ß2-adrenergic receptor agonist that induces mitochondrial biogenesis in vitro and in vivo. Formoterol increased mitochondrial biogenesis and restored mitochondrial morphology and the injury-induced changes to the organization of the actin cytoskeleton in podocytes. Importantly, ß2-adrenergic receptors were found to be present on podocyte membranes. Their knockdown attenuated formoterol-induced mitochondrial biogenesis. To determine the potential clinical relevance of these findings, mouse models of acute nephrotoxic serum nephritis and chronic (Adriamycin [doxorubicin]) glomerulopathy were used. Mice were treated with formoterol post-injury when glomerular dysfunction was established. Strikingly, formoterol accelerated the recovery of glomerular function by reducing proteinuria and ameliorating kidney pathology. Furthermore, formoterol treatment reduced cellular apoptosis and increased the expression of the mitochondrial biogenesis marker PGC-1α and multiple electron transport chain proteins. Thus, our results support ß2-adrenergic receptors as novel therapeutic targets and formoterol as a therapeutic compound for treating podocytopathies.

Mitochondrial Biogenesis as a Pharmacological Target: A New Approach to Acute and Chronic Diseases.

Mitochondrial dysfunction is a key pathophysiological component of many acute and chronic diseases. Maintenance of mitochondrial homeostasis through the balance of mitochondrial turnover, fission and fusion, and generation of new mitochondria via mitochondrial biogenesis is critical for tissue health. Pharmacological activation of mitochondrial biogenesis can enhance oxidative metabolism and tissue bioenergetics, and improve organ function in conditions characterized by mitochondrial dysfunction. However, owing to the complexity of mitochondrial assembly and maintenance, identification of specific activators of mitochondrial biogenesis has been difficult. This review provides an overview of the role of mitochondrial dysfunction in acute and chronic diseases, details the current state of therapeutics for the stimulation of mitochondrial biogenesis and their effects on disease outcomes, describes new screening methodologies to identify novel stimulators and noncanonical pathways of mitochondrial biogenesis, and discusses potential hurdles of mitochondrial biogenesis as a therapeutic strategy.

Proximal Tubule ß 2-Adrenergic Receptor Mediates Formoterol-Induced Recovery of Mitochondrial and Renal Function after Ischemia-Reperfusion Injury.

Acute kidney injury (AKI) is the rapid loss of renal function after an insult, and renal proximal tubule cells (RPTCs) are central to the pathogenesis of AKI. The ß 2-adrenergic receptor (ß 2AR) agonist formoterol accelerates the recovery of renal function in mice after ischemia-reperfusion injury (IRI) with associated rescue of mitochondrial proteins; however, the cell type responsible for this recovery remains unknown. The role of RPTCs in formoterol-induced recovery of renal function was assessed in a proximal tubule-specific knockout of the ß 2AR (γGT-Cre:ADRB2Flox/Flox). These mice and wild-type controls (ADRB2Flox/Flox) were subjected to renal IRI, followed by once-daily dosing of formoterol beginning 24 hours post-IRI and euthanized at 144 hours. Compared with ADRB2Flox/Flox mice, γGT-Cre:ADRB2Flox/Flox mice had decreased renal cortical mRNA expression of the ß 2AR. After IRI, formoterol treatment restored renal function in ADRB2Flox/Flox but not γGT-Cre:ADRB2Flox/Flox mice as measured by serum creatinine, histopathology, and expression of kidney injury marker-1 (KIM-1). Formoterol-treated ADRB2Flox/Flox mice exhibited recovery of mitochondrial proteins and DNA copy number, whereas γGT-Cre:ADRB2Flox/Flox mice treated with formoterol did not. Analysis of mitochondrial morphology by transmission electron microscopy demonstrated that formoterol increased mitochondrial number and density in ADRB2Flox/Flox mice but not in γGT-Cre:ADRB2Flox/Flox mice. These data demonstrate that proximal tubule ß 2AR regulates renal mitochondrial homeostasis. Formoterol accelerates the recovery of renal function after AKI by activating proximal tubule ß 2AR to induce mitochondrial biogenesis and demonstrates the overall requirement of RPTCs in renal recovery.

Identification of dual mechanisms mediating 5-hydroxytryptamine receptor 1F-induced mitochondrial biogenesis.

Our laboratory recently made the novel observation that 5-hydroxytryptamine 1F (5-HT1F) receptor activation induces mitochondrial biogenesis (MB), the production of new, functional mitochondria, in vitro and in vivo. We sought to determine the mechanism linking the 5-HT1F receptor to MB in renal proximal tubule cells. Using LY344864 , a selective 5-HT1F receptor agonist, we determined that the 5-HT1F receptor is coupled to Gαi/o and induces MB through Gßγ-dependent activation of Akt, endothelial nitric oxide synthase (eNOS), cyclic guanosine-monophosphate (cGMP), protein kinase G (PKG), and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). We also report that the 5-HT1F receptor signals through a second, Gßγ-dependent pathway that is linked by Akt phosphorylation of Raf. In contrast to the activated Akt pathway, Raf phosphorylation reduced extracellular signal regulated kinases (ERK1/2) and foxhead box O3a (FOXO3a) phosphorylation, suppressing an inhibitory MB pathway. These results demonstrate that the 5-HT1F receptor regulates MB through Gßγ-dependent dual mechanisms that activate a stimulatory MB pathway, Akt/eNOS/cGMP/PKG/PGC-1α, while simultaneously repressing an inhibitory MB pathway, Raf/MEK/ERK/FOXO3a. Novel mechanisms of MB provide the foundation for new chemicals that induce MB to treat acute and chronic organ injuries.