From Deficiency to Therapy: Systemic Consequences of ALAS1 Disruption and the Protective Role of 5-ALA.

Heme, an essential prosthetic group involved in mitochondrial respiration and transcriptional regulation, is synthesized via the rate-limiting enzyme 5-aminolevulinic acid synthase (ALAS). Utilizing heterozygous mouse models for ALAS1 and ALAS2, our studies have revealed diverse systemic consequences of chronic heme deficiency. ALAS1-heterozygous (ALAS1+/-) mice develop metabolic dysfunction characterized by insulin resistance, glucose intolerance, and abnormal glycogen accumulation, linked mechanistically to reduced AMP-activated protein kinase (AMPK) signaling. These mice also exhibit pronounced mitochondrial dysfunction, impaired autophagy, and accelerated aging phenotypes, including sarcopenia and metabolic decline, highlighting heme's role as a critical metabolic regulator. Additionally, ALAS2 heterozygosity (ALAS2+/-) leads to impaired erythropoiesis, resulting in anemia and ineffective iron utilization. Importantly, supplementation with the heme precursor 5-aminolevulinic acid (5-ALA) significantly mitigates ALAS1+/- phenotypes, restoring metabolic function, mitochondrial health, autophagy, and immune competence. This review encapsulates key findings from our group's research together with advances made by multiple research groups over the past decade, collectively establishing heme homeostasis as a central regulator of systemic physiology and highlighting the therapeutic potential of 5-ALA in treating heme-deficient pathologies.